Synthesis of carboxylic acids by hydration and oxidation of alkynes
An efficient method for the oxidative cleavage of internal and terminal alkynes to carboxylic acids using a combination of RuO2/Oxone/NaHCO3 in a CH3CN/H2O/EtOAc solvent system is described. Various alkynes, regardless of their electron density, were oxidized to carboxylic acids in excellent yield.
D. Yang, F. Chen, Z.-M. Dong, D.-W. Zhang, J. Org. Chem., 2004, 69, 209-212.
The presence of catalytic amounts of carbon tetrabromide enables an aerobic photooxidative cleavage of carbon-carbon triple bonds to carboxylic acids under photoirradiation.
T. Yamaguchi, T. Nobuta, Y. Kudo, S.-i. Hirashima, N. Tada, T. Miura, A. Itoh, Synlett, 2013, 24, 607-610.
A metal-free esterification of a broad range of alkynes with alcohols in the presence of phenyliodine bis(trifluoroacetate) produces esters in good yields via carbon triple bond cleavage. The transformation proceeds via hydroxyethanones and ethanediones as intermediates and exhibits a broad substrate scope and good functional group tolerance.
Q. Jiang, A. Zhao, B. Xu, J. Jia, X. Liu, C. Guo, J. Org. Chem., 2014, 79, 2709-2715.
Half-sandwich ruthenium complexes activate terminal alkynes toward anti-Markovnikov hydration and reductive hydration under mild conditions. Propargylic alcohols can be converted to 1,3-diols in high yield and with retention of stereochemistry at the propargylic position. The method is also amenable to formal anti-Markovnikov reductive amination and oxidative hydration reactions to access linear amines and carboxylic acids, respectively.
M. Zeng, S. B. Herzon, J. Org. Chem., 2015, 80, 8604-8618.
The reaction of alkyl-substituted sec-ethoxyalkynyl acetates with water catalyzed by Hg(OTf)2 afforded α,β-unsaturated esters in excellent yield with high catalytic turnover under very mild reaction conditions with virtually complete E-selectivity.
M. Nishizawa, H. Hirakawa, Y. Nakagawa, H. Yamamoto, K. Namba, H. Imagawa, Org. Lett., 2007, 9, 5577-5580.
An iodo Meyer-Schuster rearrangement of 3-alkoxypropargyl alcohols using iodine or NIS in dichloromethane at ambient temperature produces α-iodo-α,β-unsaturated esters in good yields. Secondary alcohols gave Z-isomers exclusively.
S. Puri, N. Thirupathi, M. S. Reddy, Org. Lett., 2014, 16, 5246-5249.