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Synthesis of α-hydroxy carboxylic acids, esters and amides



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In the presence of CsF, a wide range of α-substituted α-siloxy silanes were carboxylated under 1 atm of CO2 via Brook rearrangement. Various α-substituents including aryl, alkenyl, and alkyl groups were tolerated to afford α-hydroxy acids in good yields. A one-pot synthesis from aldehydes using PhMe2SiLi and CO2 provides α-hydroxy acids without the need for isolation of the α-hydroxy silane.
T. Mita, Y. Higuchi, Y. Sato, Org. Lett., 2014, 16, 14-17.

Use of a masked acyl cyanide (MAC) reagent bearing a tert-butyldimethylsilyl group allows the synthesis of α-siloxy esters via a one-pot reaction with various aldehydes and alcohols.
H. Nemoto, R. Ma, T. Kawamura, K. Yatsuzuka, M. Kamiya, M. Shibuya, Synthesis, 2008, 3819-3827.

α-Acetoxy esters or amides were synthesized directly and in one portion from aldehydes and alcohols or amines by one-carbon homologation using a masked acyl cyanide reagent bearing an acetyl group.
H. Nemoto, T. Kawamura, K. Kitasaki, K. Yatsuzuka, M. Kamiya, Y. Yoshioka, Synthesis, 2009, 1694-1702.

A one-pot method allows the synthesis of α-siloxy-Weinreb amides from aldehydes using N,O-dimethylhydroxylamine and a masked acyl cyanide reagent bearing a tert-butyldimethylsilyl group. The TBS group avoids the competitive reaction toward N-methoxy-N-methyl-2-amino-1-siloxymalononitrile.
H. Nemoto, R. Ma, H. Moriguchi, T. Kawamura, M. Kamiya, M. Shibuya, J. Org. Chem., 2007, 72, 9850-9853.