Di-tert-butyl peroxide (DTBP)
Di-tert-butyl peroxide is a very stable organic peroxide, that is often used a radical initiator, as it performs homolysis at temperatures above 100°C.
An esterification of primary benzylic C-H bonds with carboxylic acids using di-tert-butyl peroxide as an oxidant is catalyzed by novel ionic iron(III) complexes containing an imidazolinium cation. The reaction offers a broad generality and tolerates sterically hindered starting materials.
B. Lu, F. Zhu, H.-M. Sun, Q. Shen, Org. Lett., 2017, 19, 1132-1135.
In the presence of a catalytic amount of copper(II) acetate and di-tert-butyl peroxide, a cross-coupling reaction of anilines with alkylborane reagents gives N-alkylated anilines in good to excellent yields. Phenols are also applicable for this reaction.
S. Sueki, Y. Kuninobu, Org. Lett., 2013, 15, 1544-1547.
The key to the success of a general catalytic procedure for the cross-coupling of primary amides and alkylboronic acids was the identification of a mild base (NaOSiMe3) and oxidant (di-tert-butyl peroxide) to promote the copper-catalyzed reaction in high yield. This transformation provides a facile, high-yielding method for the monoalkylation of amides.
S. A. Rossi, K. W. Shimkin, Q. Xu, L. M. Mori-Quiroz, D. A. Watson, Org. Lett., 2013, 15, 2314-2317.
An efficient copper-catalyzed amidation of benzylic hydrocarbons and inactive aliphatic alkanes with simple amides proceeded smoothly without any ligand. A wide range of N-alkylated aromatic and aliphatic amides, sulfonamides, and imides were synthesized in good yields.
H.-T. Zeng, J.-M. Huang, Org. Lett., 2015, 17, 4276-4279.
An earth-abundant iron catalyst enables a dehydrogenative acylation of enamides with aldehydes to provide valuable β-ketoenamides with excellent functional group tolerance. The C-H acylation occurs with absolute Z-selectivity.
R.-H. Liu, Z.-Y. Shen, C. Wang, T.-P. Loh, X.-H. Hu, Org. Lett., 2020, 22, 944-949.
A convenient Fe-catalyzed A-D-A-T-type radical-dual-difunctionalization and cross-coupling of two different alkenes provides chain elongated and trifluoromethylated aromatic alkenes.
J. Zhao, R.-X. Liu, C.-P. Luo, L. Yang, Org. Lett., 2020, 22, 6776-6779.
A convenient method for the synthesis of aryl thioamides from aryl aldehydes and tetramethylthiuram disulfide (TMTD) in the presence of CuI and di-tert-butyl peroxide (DTBP) avoids the use of a sulfurating reagent. The protocol offers broad substrate scope, very good yields, operability and uses commercially available and inexpensive raw materials.
M.-T. Zeng, M. Wang, H.-Y. Peng, Y. Cheng, Z.-B. Dong, Synthesis, 2018, 50, 644-650.
Regiospecific radical reactions of β-alkyl nitroalkenes with sulfonyl hydrazides provide allyl sulfones with high regioselectivity in the presence of dimethylformamide (DMF), whereas reactions in acetonitrile provide vinyl sulfones.
Y. Wang, G. Xiong, C. Zhang, Y. Chen, J. Org. Chem., 2021, 86, 4018-4026.
The use of DTBP as radical initiator and a copper salt as promoter enables the preparation of allylic alcohol, benzyl, and alkane derivatives via a radical mechanism. The C(sp3)-H bond in various alcohols, toluene derivatives, and alkanes were successfully alkenylated with β-nitrostyrenes to yield the desired products in good yields.
S.-r. Guo, Y.-q. Yuan, Synlett, 2015, 26, 1961-1968.
An efficient method enables the synthesis of α-cyanomethyl-β-dicarbonyls in good yields from MeCN and simple 1,3-dicarbonyls. A radical mechanism is proposed.
C. Wang, Y. Li, M. Gong, Q. Wu, J. Zhang, J. K. Kim, M. Huang, Y. Wu, Org. Lett., 2016, 18, 4151-4153.
An efficient coupling of arylboronic acids with dimethyldisulfide under metal-free conditions provides aryl methyl sulfides. The method offers operational simplicity, satisfactory yields, excellent functional-group tolerance, as well as mild reaction conditions.
X.-m. Wu, J.-m. Lou, G.-b. Yan, Synlett, 2016, 27, 2269-2273.
The use of inorganic sodium metabisulfite as the sulfur dioxide surrogate and di-tert-butyl peroxide as source of the methyl radical enables a direct C-H methylsulfonylation of alkenes. This method provides convenient access to (E)-2-methyl styrenyl sulfones in good yields.
F.-S. He, Y. Gong, P. Rojsitthisak, J. Wu, J. Org. Chem., 2019, 84, 13159-13163.
An iron-catalyzed α-C(sp3)-H activation of cyclic and acyclic ethers provides an efficient and green method for the synthesis of mixed acetals in very good yields. The robustness of this protocol is demonstrated by the late-stage oxidation of a structurally complex natural product.
W. Han, L. Cheng, H. Zhao, Synlett, 2020, 31, 1400-1403.
A regioselective oxidative allylic C(sp3)-H arylation of readily available unactivated terminal and internal olefins with a broad range of heteroaryl boronic acids is catalyzed by cheap, abundant, and nontoxic Cu2O. This method does not require traditional coupling partners with preinstalled leaving groups at the allylic position, thus offering an alternative method to allylic arylation.
S. Pal, M. Cotard, B. Gérardin, C. Hoarau, C. Schneider, Org. Lett., 2021, 23, 3130-3135.
Copper(I) salts catalyze a synthesis of multisubstituted furans from readily available acetophenones and electron-deficient alkynes via direct C(sp3)-H bond functionalization under radical reaction conditions in the presence of di-tert-butyl peroxide as an external oxidant. This method offers an efficient access to biologically important scaffolds from simple compounds.
S. Manna, A. P. Antonchick, Org. Lett., 2015, 17, 4300-4303.
A radical-promoted cross-dehydrogenative coupling strategy enables a metal- and base-free one-pot synthesis of 2,5-diaryl 1,3,4-oxadiazoles via N-acylation of aryl tetrazoles with aryl aldehydes, followed by thermal rearrangement. A broad range of aryl tetrazoles and aryl aldehydes deliver the corresponding products in good yields.
L. Wang, J. Cao, Q. Chen, M. He, J. Org. Chem., 2015, 80, 4743-4748.
Cascade reactions of saturated cyclic amines with 2-oxo-2-arylacetic acids enable a highly regioselective and versatile synthesis of acylated N-heterocycles. In this cascade process, the copper catalyst is believed to play a crucial role not only in dehydrogenation but also in the decarboxylation and cross coupling reaction.
X. Shi, X. Chen, M. Wang, X. Zhang, X. Fan, J. Org. Chem., 2018, 83, 6524-6533.
A copper-catalyzed sp3 C-H functionalization of 2-alkyl-N-substituted benzamides provides an efficient approach to various functionalized isoindolinones without preparation of halogenated substitutes, use of expensive transition metals, or toxic Sn or CO gas.
K. Nozawa-Kumada, J. Kadokawa, T. Kameyama, Y. Kondo, Org. Lett., 2015, 17, 4479-4481.
A transition-metal-free, iodine-mediated oxidative intramolecular amination of anilines provides indolines via cleavage of unactivated (sp3)C-H and N-H bonds. The reaction could be performed on a gram scale for the synthesis of functionalized indolines.
J. Long, X. Cao, L. Zhu, R. Qiu, C.-T. Au, S.-F. Yin, T. Iwasaki, N. Kambe, Org. Lett., 2017, 19, 2793-2796.
Iodine-catalyzed cascade reactions of substituted thiophenols with alkynes under metal- and solvent-free conditions enable the synthesis of benzothiophene derivatives in good yields. Such an efficient, economical, and green transformation should provide an attractive approach to various benzothiophenes.
K. Yan, S. Yang, M. Zhang, W. Wei, Y. Liu, L. Tian, H. Wang, Synlett, 2015, 26, 1890-1894.
Copper-catalyzed C-H bond activation enables a facile, efficient, and simple protocol for direct oxidative C-H amination of benzoxazoles with primary amines using tert-butyl peroxide (TBP) as oxidant under air. Various substituted aminobenzoxazoles were synthesized with very good yields.
J. Gu, C. Cai, Synlett, 2015, 26, 639-642.
Triggered by alkyl radicals, varieties of 2-isocyanoaryl thioethers containing aliphatic, aryl, and heteroaromatic groups can be cleaved and precisely reinstalled to give benzothiazole derivatives. Mechanistic studies reveal that the cascade reaction undertakes an intermolecular pathway.
K. Luo, W.-C. Yang, K. Wei, Y. Liu, J.-K. Wang, L. Wu, Org. Lett., 2019, 21, 7851-7856.
A copper/iodine cocatalyzed decarboxylative cyclization of α-amino acids with either 2-benzoylpyridines or 2-benzoylquinolines provides 1,3-disubstituted imidazo[1,5-a]pyridines and 1,3-disubstituted imidazo[1,5-a]quinolines in excellent yields.
H. Wang, W. Xu, L. Xin, W. Liu, Z. Wang, K. Xu, J. Org. Chem., 2016, 81, 3681-3687.
Pharmaceutically important azolo[1,5-a]pyrimidines can be synthesized from widely available 3- or 5-aminoazoles, aldehydes, and triethylamine. The key is the in situ generation of an acyclic enamine followed by an annulation reaction. This strategy is capable of constructing a range of 5,6-unsubstituted pyrazolo[1,5-a]pyrimidines and [1,2,4]triazolo[1,5-a]pyrimidines.
Q. Gao, Z. Sun, Q. Xia, R. Li, W. Wang, S. Ma, Y. Chai, M. Wu, W. Hu, P. Ábrányi-Baloghm G. M. Keserű, X. Han, Org. Lett., 2021, 23, 2621-2625.
An iron(III)-catalyzed oxidative coupling of alcohols/methyl arenes with 2-amino phenyl ketones provides a broad range of 4-quinolones. Alcohols and methyl arenes are oxidized to the aldehyde in the presence of an iron catalyst and di-tert-butyl peroxide, followed by condensation with amine/Mannich-type cyclization/oxidation.
S. B. Lee, Y. Jang, J. Ahn, S. Chun, D.-C. Oh, S. Hong, Org. Lett., 2020, 22, 8382-8386.
A simple switch in reaction conditions enables facile and efficient syntheses of various valuable 3-aryl- and 3-aroylcoumarins by direct arylation and aroylation of coumarins with glyoxals in a metal-free manner. This approach accommodates a broad substrate scope and high yields of the two types of cross-coupling reactions starting from identical starting materials.
A. Moazzam, M. Khodadadi, F. Jafarpour, M. Ghandi, J. Org. Chem., 2022, 87, 3630-3637.
A copper-catalyzed direct amination of cyclic amides in DMF forms aromatic heterocyclic amines with readily available reagents via a radical mechanism. The coordinating effect of the N1 atom provides assistance to the copper ions for the activation and amination of C-O bonds.
P. Chen, K. Luo, X. Yu, X. Yuan, X. Liu, J. Lin, Y. Jin, Org. Lett., 2020, 22, 6547-6551.