Synthesis of aldehydes by oxidation of alkenes
The use of tert-butyl nitrite as a simple organic redox cocatalyst instead of copper or silver salts enabled an aldehyde-selective aerobic Wacker-Tsuji oxidation. Various aldehydes could beg isolated as major products in up to 30/1 regioselectivity as well as good to high yields at room temperature.
X.-S. Ning, M.-M. Wang, C.-Z. Yao, X.-M. Chen, Y.-B. Kang, Org. Lett., 2016, 18, 2700-2703.
In the presence of PdCl2(MeCN)2, 1,4-benzoquinone, and t-BuOH, aryl-substituted olefins can selectively be oxidized to aldehydes. In this efficient and aldehyde-selective Wacker oxidation, very good yield of aldehyde can be obtained, and up to 99% selectivity can be achieved with styrene-related substrates.
P. Teo, Z. K. Wickens, G. Dong, R. H. Grubbs, Org. Lett., 2012, 14, 3237-3239.
A mild and operationally simple protocol for the selective aerobic oxidation of aromatic olefins to carbonyl compounds is catalyzed by a Fe(III) species bearing a pyridine bisimidazoline ligand at 1 atm of O2. The method cleaves α- and β-substituted styrenes to afford benzaldehydes and aromatic ketones in high yields with excellent chemoselectivity and very good functional group tolerance.
A. Gonzalez-de-Castro, J. Xiao, J. Am. Chem. Soc., 2015, 137, 8206-8218.
A ruthenium catalyst bearing a fused π-conjugated imidazo[1,2-a][1,8]naphthyridine-based abnormal N-heterocyclic carbene ligand enables a selective oxidation of C═C bonds in a broad range of substrate to aldehydes and C≡C bonds to α-diketones in an EtOAc/CH3CN/H2O solvent mixture at room temperature.
P. Daw, R. Petakamsetty, A. Sarbajna, S. Laha, R. Ramapanicker, J. K. Bera, J. Am. Chem. Soc., 2014, 136, 13987-13990.
Osmium tetroxide has been microencapsulated in a polyurea matrix. These microcapsules have been effectively used as recyclable catalysts in the dihydroxylation and the oxidative cleavage of olefins.
S. V. Ley, C. Ramarao, A.-L. Lee, N. Ostergaard, S. C. Smith, I. M. Shirley, Org. Lett., 2003, 5, 185-187.
The use of PhI(OAc)2 in dichloromethane enables a clean oxidative cleavage of 1,2-diols to aldehydes. In the presence of OsO4 as catalyst, NMO and 2,6-lutidine, olefinic bonds can be cleaved in acetone/water to yield the corresponding carbonyl compounds.
K. C. Nicolaou, V. A. Adsool, C. R. H. Hale, Org. Lett., 2010, 12, 1552-1555.
A gold(I)-catalyzed oxidative cleavage of alkenes with tert-butyl hydrogenperoxide (TBHP) as the oxidant in the presence of neocuproine afforded ketones or aldehydes as products.
D. Xing, B. Guan, G. Cai, Z. Fang, L. Yang, Z. Shi, Org. Lett., 2006, 8, 693-696.
A series of symmetrical and unsymmetrical stilbenes bearing electron-withdrawing groups were oxidatively cleaved to the corresponding aldehydes in high yield by electrocatalytic anodic oxidation employing a high oxidation potential triphenylamine electrocatalyst. The oxidations apparently involve the corresponding 1,2-diols, which are also converted to aldehydes in high yield under the same conditions.
X. Wu, A. P. Davis, A. J. Fry, Org. Lett., 2007, 9, 5633-5636.
Palladium-catalyzed oxygenation of allyl arenes or alkenes produce (E)-alkenyl aldehydes with high yields. Allylic C-H bond cleavages occur under mild conditions during this process. Mechanistic studies show that oxygen source is water.
H. Chen, H. Jiang, C. Cai, J. Dong, W. Fu, Org. Lett., 2011, 13, 992-994.
A catalytic amount of a composite material, RuO2/BaTi4O9, in combination with NaIO4 in EtOAc-H2O has been shown to efficiently cleave alkenes, affording ketones, aldehydes and/or carboxylic acids in high yields.
H. Okumoto, K. Ohtsuko, S. Banjoya, Synlett, 2007, 3201-3205.
Specific oxidation protocols have been developed for the cleavage of styrenes, aliphatic olefins, and terminal aliphatic olefins to carbonyl compounds with ruthenium trichloride as catalyst. Olefins that are not fully substituted are converted to aldehydes rather than carboxylic acids.
D. Yang, C. Zhang, J. Org. Chem., 2001, 66, 4814-4818.
The use of Oxone allows the conversion of various aryl-, heteroaryl-, alkenyl-, and alkyltrifluoroborates into the corresponding oxidized products in excellent yields. This method tolerates a broad range of functional groups, and in secondary alkyl substrates it was demonstrated to be completely stereospecific.
G. A. Molander, L. N. Cavalcanti, J. Org. Chem., 2011, 76, 623-630.
The oxidative cleavage of C=C bonds adjacent to aryl and alkyl moieties was efficiently achieved with monoacetylated bishydroperoxides. Base-mediated fragmentation of monoacetylated bishydroperoxides generates singlet molecular oxygen as active oxidant in situ. All the reactions furnished the respective carbonyl compounds in good yields at room temperature within short reaction times.
D. Azarifar, Z. Najminejad, Synlett, 2013, 24, 1377-1382.