A (bpy)CuI/TEMPO catalyst system enables an efficient and selective aerobic oxidation of a broad range of primary alcohols, including allylic, benzylic, and aliphatic derivatives, to the corresponding aldehydes using readily available reagents, at room temperature with ambient air as the oxidant. The catalyst system is compatible with a wide range of functional groups and shows a high selectivity for 1° alcohols.
J. M. Hoover, S. S. Stahl, J. Am. Chem. Soc., 2011, 133, 16901-16910.
The combination of TEMPO and CAN can be used for the aerobic oxidation of benzylic and allylic alcohols into their corresponding carbonyl compounds. However, steric hindrance has been observed to impede the reaction with some substituted allylic systems. The present method is superior to others currently available due to its relatively short reaction times and excellent yields.
S. S. Kim, H. C. Jung, Synthesis, 2003, 2135-2137.
A convenient method enables the preparation of a silica gel supported TEMPO catalyst. The catalyst prepared from [4-hydroxy-TEMPO + NaCl]/SiO2 was used for an aerobic oxidation of alcohols to carbonyls under mild reaction conditions in the presence of Fe(NO3)3 • 9 H2O. Alcohols were converted to the corresponding carbonyls in good to excellent yields. After a simple filtration, the catalyst can be reused at least six times.
N. Tamura, T. Aoyama, T. Takido, M. Kodomari, Synlett, 2012, 23, 1397-1407.
TEMPO-derived reagents tagged with multiple perfluoroalkyl chains and triazole moieties promote the oxidation of alcohols to aldehydes in organic solvent/water mixtures with reaction rates comparable to homogeneous TEMPO reagents, but can be easily recovered by liquid/emulsion filtration.
A. Gheorghe, T. Chinnusamy, E. Cuevas-Yañez, P. Hilgers, O. Reiser, Org. Lett., 2008, 10, 4171-4174.
A robust and effective Pd catalyst for the aerobic oxidation of various alcohols has been discovered. Using a slightly higher concentration of acetic acid as additive and extending the reaction times, the oxidation can be carried out under ambient atmosphere of air.
D. R. Jensen, M. J. Schultz, J. A. Mueller, M. S. Sigman, Angew. Chem. Int. Ed., 2003, 42, 3810-3813.
Pd/C in aqueous alcohol with molecular oxygen, sodium borohydride, and potassium carbonate efficiently oxidized benzylic and allylic alcohols. Sodium borohydride allows a remarkable reactivation of active sites of the Pd surface.
G. An, M. Lim, K.-S. Chun, H. Rhee, Synlett, 2007, 95-98.
A new, highly recoverable palladium-based catalyst for the aerobic oxidation of alcohols combines an organic ligand and mesoporous channels that led to enhanced activity, prevention of agglomeration and the generation of a durable catalyst.
B. Karimi, S. Abedi, J. H. Clark, V. Budarin, Angew. Chem. Int. Ed., 2006, 45, 4776-4779.
Optimized selective aerobic oxidations in ionic liquids convert various activated primary alcohols into their corresponding acids or aldehydes in good to excellent yields. The newly developed catalytic systems could also be recycled and reused for three runs without any significant loss of catalytic activity.
N. Jiang, A. J. Ragauskas, J. Org. Chem., 2007, 72, 7030-7033.
The reaction of KBrO3 and NH2OH • HCl in situ generates NOx and Br anion, which allows in the presence of 2,2,6,6-tetramethylpiperidine-N-oxide (TEMPO) an activation of dioxygen to oxidize various benzylic alcohols quantitatively to their corresponding carbonyl compounds under mild conditions.
G. Yang, W. Wang, W. Zhu, C. An, X. Gao, M. Song, Synlett, 2010, 437-440.
Pd/C along with NaBH4 in aqueous ethanol or methanol and either K2CO3 or KOH as base at room temperature under molecular oxygen or air is capable of oxidizing alcohols to its desired carbonyl or carboxyl counterpart. Room temperature reaction in aqueous system and recyclability of the catalyst make the process safe and cheaper.
G. An, H. Ahn, K. A. De Castro, H. Rhee, Synthesis, 2010, 477-485.
The visible-light mediated oxidative C-C bond cleavage of aldehydes has been achieved in good yields at ambient temperature and open to air using Ru(bpy)3Cl2 as the photoredox catalyst.
H. Sun, C. Yang, F. Gao, Z. Li, W. Xia, Org. Lett., 2013, 15, 624-627.
A facile synthesis of aryl carboxylic acids from aryl ketones by aerobic photooxidation using the inexpensive and easily handled CBr4 as catalyst is applicable to inert compounds under usual photo-irradiation conditions, and appears very attractive for the expansion of the Norrish Type I reaction.
S.-i. Hirashima, T. Nobuta, N. Tada, A. Itoh, Synlett, 2009, 2017-2019.
A method for generating (E)-α,β-unsaturated aldehydes from Z- or E-allylic alcohols involves a Cu-catalyzed oxidation followed by an organocatalytic Z/E-isomerization with N,N-dimethylaminopyridine (DMAP).
D. Könning, W. Hiller, M. Christmann, Org. Lett., 2012, 14, 5258-5261.
A practical aerobic oxidation of propargylic alcohols using Fe(NO3)3•9H2O, TEMPO and sodium chloride in toluene at room temperature allows the conversion of propargylic alcohols to α,β-unsaturated alkynals or alkynones in good to excellent yields. This protocol can also be applied in industrial-scale production.
J. Liu, X. Xie, S. Ma, Synthesis, 2012, 44, 1569-1576.
Allylic alcohols were oxidized into aldehydes or ketones in the presence of oxygen and Et3N using Pd(OAc)2 as catalyst. Diols with one allylic function were selectively oxidized, with one of the hydroxyl groups remaining untouched.
F. Batt, E. Bourcet, Y. Kassab, F. Fache, Synlett, 2007, 1869-1872.
Adsorbed [RuCl2(p-cymene)]2 on activated carbon is an efficient, environmentally attractive and highly selective catalyst for use in aerobic oxidations, hydrolytic oxidations and dehydrations. The heterogeneous catalyst was recovered quantitatively by simple filtration and could be reused with minimal loss of activity.
E. Choi, C. Lee, Y. Na, S. Chang, Org. Lett., 2002, 4, 2369-2371.
An aerobic oxidation of primary and secondary alcohols to aldehydes and ketones using TEMPO-CuCl as catalyst in the ionic liquid [bmin][PF6] has been developed. The system needs no bubbling of O2 due to its good solubility in the ionic liquid. The resulting aldehydes (with no traces of carboxylic acids) and ketones can be extracted with organic solvents. The ionic liquid can be reused after washing with water and drying under high vacuum (8 runs for the oxidation of benzyl alcohol: yields of 72%, 70, 68, 70, 65, 64, 62, and 60).
I. A. Ansari, R. Gree, Org. Lett., 2001, 1507-1509.
A four-component system consisting of acetamido-TEMPO/Cu(ClO4)2/TMDP/DABCO in DMSO allows an efficient room-temperature aerobic alcohol oxidation of various alcohols into their corresponding aldehydes or ketones in good to excellent yields. The catalytic system can be recycled.
N. Jiang, A. J. Ragauskas, J. Org. Chem., 2006, 71, 7087-7090.
The system Cu(ClO4)2/acetamido-TEMPO/DMAP catalyses the room-temperature aerobic oxidation of primary alcohols to aldehydes in the ionic liquid [bmpy]PF6. The catalysts can be recycled and reused.
N. Jiang, A. J. Ragauskas, Org. Lett., 2005, 7, 3689-3692.
1 mol-% TEMPO and a catalytic amount of 1,3-dibromo-5,5-dimethylhydantoin and NaNO2 is a highly efficient catalytic system for the aerobic oxidations of benzylic alcohols in water.
R. Liu, C. Dong, X. Liang, X. Wang, X. Hu, J. Org. Chem., 2005, 70, 239-244.
Oxidation of alcohols to aldehydes and ketones were performed under atmospheric oxygen with a catalytic amount of V2O5 in toluene at 100°C. Secondary alcohols can be chemoselectively converted into ketones in the presence of primary hydroxy groups.
S. Velusamy, T. Punniyamurthy, Org. Lett., 2004, 6, 217-219.
A catalytic oxidative cleavage of 1,3-diketones enables the synthesis of the corresponding carboxylic acids by aerobic photooxidation with iodine under irradiation with a high-pressure mercury lamp.
N. Tada, M. Shomura, L. Cui, T. Nobuta, T. Miura, A. Itho, Synlett, 2011, 2896-2900.
An aerobic photooxidative cleavage of vicinal diols yields carboxylic acids using 2-chloroanthraquinone in the presence of photoirradiation with a high-pressure mercury lamp. This is a metal-free reaction in which molecular oxygen is used as the terminal oxidant.
Y. Matsusaki, T. Yamaguchi, N. Tada, T. Miura, A. Itoh, Synlett, 2012, 23, 2059-2062.
An efficient oxidation of various acetals, including open-chain acetals, 1,3-dioxanes and 1,3-dioxalanes, with molecular oxygen in the presence of catalytic amounts of N-hydroxyphthalimide (NHPI) and Co(OAc)2 as co-catalyst gave esters.
B. Karimi, J. Rajabi, Synthesis, 2003, 2373-2377.
Natural sunlight and air are enable an efficient oxidation of α-aryl halogen derivatives to the corresponding α-aryl carbonyl compounds at room temperature through the combination of photocatalysis and organocatalysis. A plausible mechanism was proposed on the basis of the mechanistic studies.
Y. Su, L. Zhang, N. Jiao, Org. Lett., 2011, 13, 2168-2171.
N-hydroxyphthalimide (NHPI) catalyzes a metal-free, aerobic oxidative cleavage of olefins. This methodology avoids the use of toxic metals or overstoichiometric amounts of traditional oxidants, showing good economical and environmental advantages. Based on the experimental observations, a plausible mechanism is proposed.
R. Lin, F. Chen, N. Jiao, Org. Lett., 2012, 14, 4158-4161.
A Wacker-type oxidation of alkynes catalyzed by PdBr2 and CuBr2 allows an efficient access to 1,2-diketones using molecular oxygen. Under optimized conditions, various alkynes give 1,2-diketones in good yield. The mechanism of this reaction was preliminarily investigated by control experiments.
W. Ren, Y. Xia, S.-J. Ji, Y. Zhang, X. Wan, J. Zhao, Org. Lett., 2009, 11, 1841-1844.
Aerobic oxidation of deoxybenzoins is efficiently catalyzed by 1,4-diazabicyclo[2.2.2]octane (DABCO) with air as the sole oxidant to give the corresponding benzils in excellent yields. The process has been successfully extended to a one-pot synthesis of quinoxalines from benzyl ketones and aromatic 1,2-diamines.
C. Qi, H. Jiang, L. Huang, Z. Chen, H. Chen, Synthesis, 2011, 387-396.
A Cu-catalyzed oxidative amidation-diketonization reaction of terminal alkynes leads to α-ketoamides. In this copper-catalyzed radical process, O2 not only participates as the ideal oxidant but also undergoes dioxygen activation under ambient conditions.
C. Zhang, N. Jiao, J. Am. Chem. Soc., 2010, 132, 28-29.
A copper-catalyzed aerobic oxidative cross-dehydrogenative coupling (CDC) of amines with α-carbonyl aldehydes leads to various α-ketoamides compounds. Many types of amines are tolerant in this transformation. Wide substrate scope, and the use of air as oxidant and initiator make this transformation highly efficient and practical.
C. Zhang, X. Zong, L. Zhang, N. Jiao, Org. Lett., 2012, 14, 3280-3283.
Iodine/base-catalyzed aerobic photooxidation of 1,3-diketones under visible-light irradiation of fluorescent lamp enables a catalytic direct synthesis of 1,2-diketones.
N. Tada, M. Shomura, H. Nakayama, T. Miura, A. Itoh, Synlett, 2010, 1979-1983.
Pd(DMSO)2(TFA)2 as a catalyst enables a direct dehydrogenation of cyclohexanones and other cyclic ketones to the corresponding enones, using O2 as the oxidant. α,β-Unsaturated carbonyl compounds are versatile intermediates in the synthesis of pharmaceuticals and biologically active compounds. The substrate scope includes heterocyclic ketones and several natural-product precursors.
T. Diao, S. S. Stahl, J. Am. Chem. Soc., 2011, 133, 14566-14569.
Use of 4,5-diazafluorenone as an ancillary ligand for Pd(OAc)2 enables terminal alkenes to be converted to linear allylic acetoxylation products in good yields and selectivity under O2. Mechanistic studies have revealed that the ligand facilitates C-O reductive elimination from a π-allyl-PdII intermediate, thereby eliminating the requirement for benzoquinone as stoichiometric oxidant in this key catalytic step.
A. N. Campbell, P. B. White, I. A. Guzei, S. S. Stahl, J. Am. Chem. Soc., 2010, 132, 15116-15119.
Imines and secondary amines were synthesized selectively by a Pd-catalyzed one-pot reaction of benzyl alcohols with primary amines. The reactions did not require any additives and were effective for a wide range of alcohols and amines.
M. S. Kwon, S. Kim, S. Park, W. Bosco, R. K. Chidrala, J. Park, J. Org. Chem., 2009, 74, 2877-2879.
Pd(II)-catalyzed ortho-hydroxylation of variously substituted benzoic acids under an athmospheric pressure of oxygen or air is achieved under nonacidic conditions. Labeling studies support a direct oxygenation of aryl C-H bonds with molecular oxygen.
Y.-H. Zhang, J.-Q. Yu, J. Am. Chem. Soc., 2009, 131, 14654-14655.
The use of flavin organocatalysts and a Hantzsch ester enabled a transition-metal-free Dakin oxidation fueled by molecular oxygen as the terminal oxidant. Catechols and electron-rich phenols are achieved with low catalyst loadings, in the presence of Hantzsch ester, and O2 or air as the stoichiometric oxidant source.
S. Chen, F. W. Foss, Jr, Org. Lett., 2012, 14, 5150-5153.
Passerini three-component reaction under catalytic aerobic conditions allows the conversion of alcohols instead of aldehydes. The reaction of alcohols, isocyanides, and carboxylic acids in toluene in the presence of a catalytic amount of cupric chloride, NaNO2, and TEMPO afforded, under an oxygen atmosphere, the P-3CR adducts in good yields.
J. Brioche, G. Masson, J. Zhu, Org. Lett., 2010, 12, 1432-1435.
Oxidative ring expansion of methylenecyclopropanes with CAN under oxygen atmosphere was investigated. A facile conversion affording 2,2-diarylcyclobutanones occurred in good yields.
V. Nair, T. D. Suja, K. Mohanan, Synthesis, 2006, 2531-2534.
A new copper-catalyzed oxidative [3 + 2] cycloaddition of alkenes with anhydrides using oxygen as the sole oxidant affords γ-lactones in good to excellent yield. This catalyzed cyclization process has a broad substrate scope.
L. Huang, H. Jiang, C. Qi, X. Liu, J. Am. Chem. Soc., 2010, 132, 17652-17654.
Several Pd-catalyzed oxidative cyclizations proceed in excellent yield under simple aerobic conditions. Importantly, this system provided entry into enatioselective catalysis with a readily available Pd-sparteine complex.
R. M. Trend, Y. K. Ramtohul, E. M. Ferreira, B. Stoltz, Angew. Chem. Int. Ed., 2003, 42, 2892-2895.
Enantioselective intramolecular oxidative amidation of alkenes has been achieved using a (pyrox)Pd(II)(TFA)2 as catalyst and O2 as the stoichiometric oxidant. The reactions proceed at room temperature in very good yields and with high enantioselectivity. Catalyst-controlled stereoselective cyclization reactions are demonstrated for a number of chiral substrates.
R. I. McDonald, P. W. White, A. B. Weinstein, C. P. Tam, S. S. Stahl, Org. Lett., 2011, 13, 2830-2833.
Use of a base-free Pd(DMSO)2(TFA)2 catalyst enables the synthesis of six-membered nitrogen heterocycles via a Wacker-type aerobic oxidative cyclization of alkenes. Various heterocycles, including morpholines, piperidines, piperazines and piperazinones, are accessible by this method.
Z. Lu, S. S. Stahl, Org. Lett., 2012, 14, 1234-1237.
In the presence of oxygen and a small amount of AIBN as radical initiator, primary amines are oxidatively coupled to imines and tertiary amines are cyanated to α-aminonitriles. These metal-free aerobic oxidative coupling reactions may find applications in a wide range of green oxidation chemistry.
L. Liu, Z. Wang, X. Fu, C.-H. Yan, Org. Lett., 2012, 14, 5692-5695.
A dioxygenation of alkenes using molecular oxygen and a simple, readily prepared hydroxamic acid derivative in th presence of a radical initiator offers an alternative to common dioxygenation processes catalyzed by precious transition metals. This transformation capitalizes on the unique reactivity profile of hydroxamic acid derivatives in radical-mediated alkene addition processes.
B. C. Giglio, V. A. Schmidt, E. J. Alexanian, J. Am. Chem. Soc., 2011, 133, 13320-13322.
An efficient base-catalyzed [3 + 3] oxidative aromatization of α,β-unsaturated carbonyl compounds with dimethyl glutaconate under mild, metal-free conditions affords substituted benzenes in high to excellent yields with oxygen as oxidant and water as sole byproduct. In situ generation of the α,β-unsaturated carbonyl compounds from aldehydes and ketones enables a more convenient tandem [3 + 2 + 1] aerobic oxidative aromatization reaction.
A. Diallo, Y.-L. Zhao, H. Wang, S.-S. Li, C.-Q. Ren, Q. Liu, Org. Lett., 2012, 14, 5776-5779.
Pd-catalyzed intermolecular aerobic dehydrogenative aromatizations enable the arylation of amines with cyclohexanones and 2-cyclohexen-1-ones. Under optimized reaction conditions, primary and secondary amines are selectively arylated in good yields under an atmosphere of molecular oxygen.
S. A. Girard, X. Hu, T. Knauber, F. Zhou, M.-O. Simon, G.-J. Deng, C.-J. Li, Org. Lett., 2012, 14, 5606-5609.
An iron-catalyzed route for the regioselective synthesis of 1,3- and 1,3,5-substituted pyrazoles from the reaction of diarylhydrazones and vicinal diols allows the conversions of a broad range of substrates.
N. Panda, A. K. Jena, J. Org. Chem., 2012, 77, 9401-9406.
A direct access to symmetrical and unsymmetrical 2,5-disubstituted [1,3,4]-oxadiazoles has been accomplished through an imine C-H functionalization of N-arylidenearoylhydrazide using a catalytic quantity of Cu(OTf)2. These reactions can be performed in air atmosphere and moisture making it exceptionally practical for application in organic synthesis.
S. Guin, T. Ghosh, S. K. Rout, A. Banerjee, B. K. Patel, Org. Lett., 2011, 13, 5976-5979.
A convenient one-pot Cu(I)-catalyzed strategy gives trisubstituted α-carbonyl furans derivatives in good yields via (2-furyl) carbene complexes using air as the oxidant.
H. Cao, H. Zhan, J. Cen, J. Lin, Y. Lin, Q. Zhu, M. Fu, H. Jiang, Org. Lett., 2013, 15, 1080-1083.
A highly efficient carbon-carbon triple bond cleavage reaction of (Z)-enynols offered a new route to highly substituted butenolides through a gold(I)-catalyzed tandem cyclization/oxidative cleavage.
Y. Liu, F. Song, S. Guo, J. Am. Chem. Soc., 2006, 128, 11332-11333.
An unprecedented ruthenium(II)-catalyzed oxidative C-N coupling method enables a facile intramolecular synthesis of various synthetically challenging tri- and tetrasubstituted pyrazoles in the presence of oxygen as oxidant. The reaction demonstrates excellent reactivity, functional group tolerance, and high yields.
J. Hu, S. Chen, Y. Sun, J. Yang, Y. Rao, Org. Lett., 2012, 14, 5030-5033.
An operationally simple, atom-economic, palladium-catalyzed cyclization reaction of N-aryl imines, affords indoles via an oxidative linkage of two C-H bonds under mild conditions in the presence of oxygen. The process allows quick assembly of indole rings from inexpensive and readily available anilines and ketones and tolerates a broad range of functional groups.
Y. Wei, I. Deb, N. Yoshikai, J. Am. Chem. Soc., 2012, 134, 9098-9101.
CuCl/DABCO/4-HO-TEMPO as the catalysts and oxygen as the terminal oxidant enabled an efficient aerobic oxidative synthesis of 2-substituted quinazolines and 4H-3,1-benzoxazines from the one-pot reaction of aldehydes with 2-aminobenzylamines and 2-aminobenzyl alcohols, respectively.
B. Han, X.-L. Yang, C. Wang, Y.-W. Bai, T.-C. Pan, X. Chen, W. Yu, J. Org. Chem., 2012, 77, 1136-1142.
A set of benzimidazoles, 3H-imidazo[4,5-b]pyridines, purines, xanthines and benzothiazoles was readily prepared from (hetero)aromatic ortho-diamines or ortho-aminothiophenol and aldehydes using chlorotrimethylsilane in DMF as a promoter and water-acceptor agent, followed by oxidation with air oxygen.
S. V. Ryabukhin, A. S. Plaskon, D. M. Volochnyuk, A. A. Tolmachev, Synthesis, 2006, 3715-3726.
The 1H-indazole skeleton can be constructed by a [3 + 2] annulation approach from arynes and hydrazones. Under different reaction conditions, both N-tosylhydrazones and N-aryl/alkylhydrazones can be used to afford various indazoles.
P. Li, C. Wu, J. Zhao, D. C. Rogness, F. Shi, J. Org. Chem., 2012, 77, 3127-3133.
An aerobic visible-light driven photoredox catalytic formation of 2-substituted benzothiazoles through radical cyclization of thioanilides features C-H functionalization and C-S bond formation with no direct metal involvement except the sensitizer. In this reaction, visible-light is the driving force, molecular oxygen the terminal oxidant, and water the only byproduct.
Y. Cheng, J. Yang, Y. Qu, P. Li, Org. Lett., 2012, 14, 98-101.
N-Arylthioureas are converted to 2-aminobenzothiazoles via intramolecular C-S bond formation/C-H functionalization in the presence of an unusual cocatalytic Pd(PPh3)4/MnO2 system under an oxygen atmosphere at 80°C. This method eliminates the need for an ortho-halo substituted precursor, instead achieving direct functionalization of the ortho-aryl C-H bond.
L. L. Joyce, R. A. Batey, Org. Lett., 2009, 11, 2792-2795.
Highly efficient conditions for the preparation of 3,3-disubstituted oxindoles by a formal C-H, Ar-H coupling of anilides have been identified using catalytic Cu(OAc)2•H2O with atmospheric oxygen as the reoxidant in mesitylene or toluene as solvent; no additional base is required.
J. E. M. N. Klein, A. Perry, D. S. Pugh, R. J. K. Taylor, Org. Lett., 2010, 12, 3446-3449.
A domino C-H functionalization of glycine derivatives for the production of a series of quinolines was achieved under catalytic radical cation salt induced conditions. A mechanism is proposed, that includes a peroxyl radical cation, which is generated by the coupling between O2 and TBPA+•.
X. Jia, F. Peng, C. Qing, C. Huo, X. Wang, Org. Lett., 2012, 14, 4030-4033.
A highly efficient α alkylation of ketones with primary alcohols by the use of a recyclable palladium catalyst has been demonstrated.
M. S. Kwon, N. Kim, S. H. Seo, I. S. Park, R. K. Cheedrala, J. Park, Angew. Chem., 2005, 117, 7073-7075.
A general and mild protocol of oxygen-promoted Pd(II) catalysis allows a selective cross-couplings of alkenyl- and arylboron compounds with various olefins. Unlike most cross-coupling reactions, this new methodology works well even in the absence of bases, consequently averting undesired homo-couplings.
K. S. Yoo, C. H. Yoon, J. W. Jung, J. Am. Chem. Soc., 2006, 128, 16348-16393.
A mild and efficient Pd(II) catalysis leads to the formation of carbon-carbon bonds between various organoboron compounds and alkenes. The resultant Pd(0) species is reoxidized by molecular oxygen to Pd(II). This protocol promotes the desired Pd(II) catalysis, whereas the competing Pd(0) pathways (Heck or Suzuki) are retarded.
Y. C. Jung, R. K. Mishra, C. H. Yoon, K. W. Jung, Org. Lett., 2003, 5, 2231-2234.
A Pd-catalyzed oxidative cross-coupling reaction of arylboronic acids with α-diazoesters using molecular oxygen as the reoxidant gives E-α,β-diarylacrylates in good yields and very high E-to-Z selectivity.
Y.-T. Tsoi, Z. Zhou, A. S. C. Chan, W.-Y. Yu, Org. Lett., 2010, 12, 4506-4509.
Terminal alkynes can be directly cross-coupled with alkylzinc reagents in the presence of a Pd catalyst at room temperature with air as the oxidant. CO was found to be critical in gaining high chemical yields and selectivities. Good yields were obtained for a wide range of alkynes and alkylzinc reagents.
M. Chen, X. Zheng, W. Li, J. He, A. Lei, J. Am. Chem. Soc., 2010, 132, 4101-4103.
A facile and environmentally friendly synthetic method for a variety of symmetrical 1,3-diyne derivatives is based on a Pd/C-CuI-catalyzed homocoupling reaction of terminal alkynes. The reaction was efficiently catalyzed by an extremely low loading of Pd/C and CuI in the presence of molecular oxygen as the oxidant without any phosphine ligands and bases.
T. Kurita, M. Abe, T. Maegawa, Y. Monguchi, H. Sajiki, Synlett, 2007, 2521-2524.
A Pd-catalyzed Wacker-type oxidative cyclization under air allows the construction of 2-methylquinolines in good yields under mild conditions.
Z. Zhang, J. Tang, Z. Wang, Org. Lett., 2008, 10, 173-175.
A direct convergent two-component synthesis of quinolines from α,β-unsaturated ketones and o-aminophenylboronic acid derivatives is regiocomplementary to the traditional Skraup-Doebner-Von Miller synthesis and proceeds under basic rather than strongly acidic conditions.
J. Horn, S. P. Marsden, A. Nelson, D. House, G. G. Weingarten, Org. Lett., 2008, 10, 4117-4120.
Aerobic oxidation of deoxybenzoins is efficiently catalyzed by 1,4-diazabicyclo[2.2.2]octane (DABCO) with air as the sole oxidant to give the corresponding benzils in excellent yields. The process has been successfully extended to a one-pot synthesis of quinoxalines from benzyl ketones and aromatic 1,2-diamines.
C. Qi, H. Jiang, L. Huang, Z. Chen, H. Chen, Synthesis, 2011, 387-396.
An efficient method enables a synthesis of 4-amino-2-aryl(alkyl)quinazolines from readily available N-arylamidines and isonitriles via palladium-catalyzed intramolecular aryl C-H amidination by isonitrile insertion.
Y. Wang, H. Wang, J. Peng, Q. Zhu, Org. Lett., 2011, 13, 4596-4599.
Palladium-catalyzed oxidative cyclocarbonylation of 2-vinylphenols enables a direct synthesis of various coumarins in good yields in the presence of low pressures of CO, and air or 1,4- benzoquinone as the oxidant. The reaction conditions are attractive in terms of environmental considerations and operational simplicity.
J. Ferguson, F. Zeng, H. Alper, Org. Lett., 2012, 14, 5602-5605.
Ruthenium supported on alumina acts as an efficient heterogeneous catalyst for the oxidation of non-activated as well as activated amines to the corresponding nitriles or imines with 1 atm of dioxygen or air.
K. Yamaguchi, N. Mizuno, Angew. Chem. Int. Ed., 2003, 42, 1480-1483.
In the presence of an easily prepared supported ruthenium hydroxide catalyst, Ru(OH)x/Al2O3, various primary azides including benzylic, allylic, and aliphatic ones could be converted into the corresponding nitriles in good yields. The Ru(OH)x/Al2O3 catalyst could be further employed for synthesis of amides in water from benzylic or aliphatic primary azides.
J. He, K. Yamaguchi, N. Mizuno, J. Org. Chem., 2011, 76, 4552-4553.
RuCl3-catalyzed oxidative cyanation of tertiary amines with sodium cyanide under molecular oxygen at 60°C gives the corresponding α-aminonitriles in excellent yields. This reaction is clean and should be an environmentally benign and useful process.
S.-I. Murahashi, N. Komiya, H. Terai, T. Nakae, J. Am. Chem. Soc., 2003, 125, 15312-15313.
A green dehydrogenation of hydrazo compounds using basic alumina or KF/alumina under solvent-free conditions afforded azo compounds in good to excellent yields.
M. Mihara, T. Nakai, T. Iwai, T. Ito, T. Mizuno, Synlett, 2007, 2124-2126.
Oxidations of organic substrates such as sulfides, secondary amines, N-hydroxylamines, and tertiary amines with molecular oxygen in the presence of 5-ethyl-3-methyllumiflavinium perchlorate catalyst and hydrazine monohydrate in 2,2,2-trifluoroethanol occur highly efficiently to give the corresponding oxidized compounds in excellent yields.
Y. Imada, H. Iida, S. Ono, S.-I. Murahashi, J. Am. Chem. Soc., 2003, 125, 2868-2869.
A regioselective one-pot synthesis of substituted pyrazoles from N-monosubstituted hydrazones and nitroolefins gives products in good yields. A key nitropyrazolidine intermediate is characterized and a plausible mechanism is proposed.
X. Deng, N. S. Mani, Org. Lett., 2006, 8, 3505-3508.
Two general protocols for the reaction of electron-deficient N-arylhydrazones with nitroolefins allow a regioselective synthesis of 1,3,5-tri- and 1,3,4,5-tetrasubstituted pyrazoles. Studies on the stereochemistry of the key pyrazolidine intermediate suggest a stepwise cycloaddition mechanism.
X. Deng, N. S. Mani, J. Org. Chem., 2008, 73, 2412-2415.
A second-generation, water-soluble cobalt catalyst for the formation of trans-THF products via the Mukaiyama aerobic oxidative cyclization gives superior yields and enables greatly simplified purification compared to the previous catalysts. Quarternization of the amino group of the ligand with MeI allows a simple, neutral water extraction.
C. Palmer, N. A. Morra, A. C. Stevens, B. Bajtos, B. P. Machin, B. L. Pagenkopf, Org. Lett., 2009, 11, 5614-5617.
An asymmetric 1,2-addition of alkyl groups to conjugated cyclic enones gave allylic alcohols with chiral quaternary centers. The resultant allylic alcohols are converted into epoxy alcohols with excellent diastereoselectivities. A semipinacol rearrangement provided α,α-dialkyl-β-hydroxy ketones with all-carbon chiral quaternary centers.
S.-J. Jeon, P. J. Walsh, J. Am. Chem. Soc., 2003, 125, 9544-9545.
Highly enantio- and diastereoselective one-pot procedures for the synthesis of epoxy alcohols involve either asymmetric addition of an alkylzinc reagent to an enal or asymmetric vinylation of an aldehyde with divinylzinc reagents. Exposure of the reaction mixtures to dioxygen and addition of catalytic titanium tetraisopropoxide yields epoxy alcohols with good to excellent yields.
A. E. Lurain, A. Maestri, A. R. Kelli, P. J. Carroll, P. J. Walsh, J. Am. Chem. Soc., 2004, 126, 13608-13609.
The oxidation of substituted toluenes by molecular oxygen to the corresponding substituted benzoic acids using Co(C18H35O2)2/NH4Br or Co(OAc)2/NaBr/AcOH as catalysts in the presence of a radical initiator in non-acidic solvents was investigated.
F. Yang, J. Sun, R. Zheng, W. Qiu, J. Tang, M. He, Tetrahedron, 2004, 60, 1225-1228.
A methyl group at an aromatic nucleus is oxidized directly to the corresponding carboxylic acid in the presence of molecular oxygen and catalytic hydrobromic acid under photoirradiation.
S.-I. Hirashima, A. Itoh, Synthesis, 2006, 1757-1759.
β-Ketoesters can directly be transformed to the corresponding α-hydroxymalonic esters, tartronic esters, with molecular oxygen catalyzed by calcium iodide under visible light irradiation from a fluorescent lamp. This convenient tandem oxidation/rearrangement reduces consumption of energy, time, and solvents.
N. Kanai, H. Nakayama, N. Tada, A. Itoh, Org. Lett., 2010, 12, 1948-1951.
Pd(OAc)2 in the presence of a BIAN ligand is an efficient catalyst system for the base-free oxidative Heck reaction that outperforms the currently available catalysts for the more challenging substrates studied. The catalyst system is highly selective, and works at room temperature with dioxygen as the oxidant.
Arylations of electron-rich heteroatom-substituted olefins were performed with electron-rich arylboronic acids via palladium(II) catalysis. This mild protocol, which offers access to functionalized enamides, exploits oxygen gas for reoxidation and a stable 1,10-phenanthroline bidentate ligand to promote the palladium(II) regeneration and to control the regioselectivity.
M. M. S. Andappan, P. Nilsson, H. v. Schenck, M. Larhed, J. Org. Chem., 2004, 69, 5212-5218.
Palladium-catalyzed oxidative Heck coupling reaction of coumarins and arylboronic acids allows a direct synthesis of 4-arylcoumarins in good yields. The reaction also showed tolerance toward functional groups such as hydro, methoxy, diethylamino, nitro, and chloro groups.
Y. Li, Z. Qi, H. Wang, X. Fu, C. Duan, J. Org. Chem., 2012, 77, 2053-2057.
An efficient copper-catalyzed oxidative trifluoromethylation of terminal alkynes and aryl boronic acids in the presence of air is successfully achieved by adding both the substrate and a portion of CF3TMS slowly using a syringe pump to the reaction mixture.
X. Jiang, L. Chu, F.-L. Qing, J. Org. Chem., 2012, 77, 1251-1257.
The chemoselective ring opening of N-tosyl aziridines with aldehydes catalyzed by an N-heterocyclic carbene gave carboxylates of 1,2-amino alcohols. A plausible mechanism for this reaction is discussed.
Y.-K. Liu, R. Li, L. Yue, B.-J. Li, Y.-C. Chen, Y. Wu, L.-S. Ding, Org. Lett., 2006, 8, 1521-1524.
An efficient CuSO4-catalyzed S-arylation of thiols with aryl and heteroaryl boronic acids at room temperature is established. A wide variety of thiols and arylboronic acids can be converted in the presence of CuSO4 as the catalyst, inexpensive 1,10-phen·H2O as the ligand, oxygen as oxidant, and EtOH as environment-friendly solvent.
H.-J. Xu, Y.-Q. Zhao, T. Feng, Y.-S. Feng, J. Org. Chem., 2012, 77, 2649-2658.
Unsymmetrical diorgano-monosulfides, selenides, and tellurides can be synthesized by the coupling of dichalcogenides with aryl- or alkylboronic acids using a copper catalyst in air. The present reaction takes advantage of both organochalcogenide groups on the dichalcogenide.
N. Taniguchi, J. Org. Chem., 2007, 72, 1241-1245.
A regio and anti-selective copper-catalyzed 1,2-hydroxysulfenylation of alkenes can be carried out by the use of disulfides and acetic acid. Reoxidation of intermediate sulfides by oxygen enables the use of both organosulfide groups of the disulfides.
N. Taniguchi, J. Org. Chem., 2006, 71, 7874-7876.
Alkenyl sulfones can be stereoselectively synthesized from alkenes or alkynes using sodium sulfinates in the presence of CuI-bpy as catalyst and oxygen. The reaction of alkenes gives (E)-alkenyl sulfones via anti addition of the sulfonyl cation followed by an elimination process. Furthermore, the employment of alkynes produces (E)-β-haloalkenyl sulfones in the presence of potassium halides.
N. Taniguchi, Synlett, 2011, 1308-1312.
Copper-catalyzed hydrosulfonylations of both terminal and internal alkynes can be carried out using sodium sulfinates in air. The procedure affords syn-selectively (E)-alkenyl sulfones in good yields.
N. Taniguchi, Synlett, 2012, 23, 1245-1249.
A mild, efficient, and general aromatization of Hantzsch 1,4-dihydropyridines with oxygen was realized at room temperature with 5 mol % of 9-phenyl-10-methylacridinium perchlorate as photocatalyst, which could be easily recovered and reused.
X. Fang, Y.-C. Liu, C. Li, J. Org. Chem., 2007, 72, 8608-8610.
In the presence of activated carbon, Hantzsch 1,4-dihydropyridines and 1,3,5-trisubstituted pyrazolines were aromatized with molecular oxygen to the corresponding pyridines and pyrazoles in excellent yields.
N. Nakamichi, Y. Kawashita, M. Hayashi, Synthesis, 2004, 1015-1020.
CuI-catalyzed coupling of 2-halobenzylamines with β-keto esters or 1,3-diketones in i-PrOH in the presence of of K2CO3 produced 1,2-dihydroisoquinolines as the cyclization products, which underwent smooth dehydrogenation under air atmosphere to afford substituted isoquinolines.
B. Wang, B. Lu, Y. Jiang, Y. Zhang, D. Ma, Org. Lett., 2008, 10, 2761-2763.
An intramolecular palladium(II)-catalyzed oxidative carbon-carbon bond formation under air in the presence of pivalic acid as the reaction solvent, instead of acetic acid, results in greater reproducibility, higher yields, and broader substrate scope. The reaction allows the conversion of both electron-rich and electron-deficient diarylamines.
B. Liégault, D. Lee, M. P. Huestis, D. R. Stuart, K. Fagnou, J. Org. Chem., 2008, 73, 5022-5028.
A mild and efficient domino reaction allows a regiospecific synthesis of polysubstituted furans in moderate yields via a copper(I)-catalyzed rearrangement/dehydrogenation oxidation/carbene oxidation sequence of 1,5-enynes in situ formed from alkynols and diethyl but-2-ynedioate.
H. Cao, H. Jiang, W. Yao, X. Liu, Org. Lett., 2009, 11, 1931-1933.
A mild, Pd(OAc)2-catalyzed regioselective cross-coupling between indoles and potassium aryltrifluoroarylborates gives 2-aryl indoles in moderate yields in the presence of Cu(OAc)2 in acetic acid at room temperature.
J. Zhao, Y. Zhang, K. Cheng, J. Org. Chem., 2008, 73, 7428-7431.
A copper(II)-catalyzed conversion of bisaryloxime ethers to 2-arylbenzoxazoles involves a cascade C-H functionalization and C-N/C-O bond formation under oxygen atmosphere.
M. M. Guru, M. A. Ali, T. Punniyamurthy, Org. Lett., 2011, 13, 1194-1197.
C-H activation of aryl triazene compounds followed by intramolecular amination in the presence of a catalytic amount of Pd(OAc)2 provides 1-aryl-1H-benzotriazoles at moderate temperature.
R. K. Kumar, M. A. Ali, T. Punniyamurthy, Org. Lett., 2011, 13, 2102-2105.
A copper-catalyzed one-pot procedure enables the synthesis of imidazo[1,2-a]pyridines with aminopyridines and nitroolefins using air as oxidant. This general reaction appears to be very suitable for the construction of various imidazo[1,2-a]pyridines.
R.-L. Yan, H. Yan, C. Ma, Z.-Y. Ren, X.-A. Gao, G.-S. Huang, Y.-M. Liang, J. Org. Chem., 2012, 77, 2024-2028.
A copper-catalyzed reaction under an atmosphere of air provides 1,2,4-triazole derivatives by sequential N-C and N-N bond-forming oxidative coupling reactions. Starting materials and the copper catalyst are readily available and inexpensive. A wide range of functional groups are tolerated.
S. Ueda, H. Nagasawa, J. Am. Chem. Soc., 2009, 131, 15080-15081.
A convenient, copper-catalyzed C-H and C-N bond activation enables an efficient and conceptually new method for oxidative amination of azoles with tertiary amines. This protocol can be performed in the absence of external base and only requires atmospheric oxygen as oxidant.
S. Guo, B. Qian, C. Xia, H. Huang, Org. Lett., 2011, 13, 522-525.
Treatment of chlorobis(methyldiphenylsilyl)methyllithium with various Grignard reagents and CuCN·2LiCl afforded 1,1-disilylalkylcopper species. Subsequent aerobic oxidation provided various acylsilanes in good yields. The preparation of 1-cyano-1-silylalkylcopper species via consecutive double 1,2-migration of alkyl and cyano groups is described.
J. Kondo, A. Inoue, Y. Ito, H. Shinokubo, K. Oshima, Tetrahedron, 2005, 61, 3361-3369.
Copper-catalyzed aerobic oxidative coupling of terminal alkynes with H-phosphonates affords alkynylphosphonates in high yields.
Y. Gao, G. Wang, L. Chen, P. Xu, Y. Zhao, Y. Zhou, L.-B. Han, J. Am. Chem. Soc., 2009, 131, 7956-7957.
A [Cu(OH)•TMEDA]2Cl2 catalyzed tandem reaction allows the synthesis of a series of sterically and electronically divergent phenacyl tertiary phosphine-boranes.
G. Kumaraswamy, G. V. Rao, A. N. Murthy, B. Sridhar, Synlett, 2009, 1180-1184.
A series of propargylic amides were transformed to the corresponding alkylideneoxazolines by a gold(I) catalyst. A subsequent autoxidation to hydroperoxides bearing the heteroaromatic oxazoles followed by reduction to the corresponding alcohols with sodium borohydride enables a highly efficient, and atom-economic access to a series of functionalized 2,5-disubstituted oxazoles.
A. S. K. Hashmi, M. C. B. Jaimes, A. M. Schuster, F. Rominger, J. Org. Chem., 2012, 77, 6394-6408.