From organocatalysed desilylations to high-yielding benzylidenations of electron-deficient benzaldehydes

Abstract

A new type of organoprecatalyst (MeSCH2Cl/KI) for desilylation and benzylidenation reactions has been designed. Both reactions are user friendly and high yielding (71–>99%) and have fast reaction rates. The desilylation of iodo silyl ethers was achieved with no sequential etherification side reactions like those seen for reactions when using TBAF. In the application of the catalytic system to a 6-TBDMS ether of a glucoside, glucoside benzylidenations using electron-deficient benzaldehydes were achieved in 87% yield compared with the previously reported yields of 69–77%. Altogether, 14 benzylidenation reactions were realised using silyloxy alcohols and electron-deficient benzaldehydes instead of their activated acetal forms. In terms of reaction rates and yields, the order of the benzylidenations is p-fluorobenzaldehyde > benzaldehyde > p-anisaldehyde, and a possible mechanism is discussed. These experiments have preliminarily differentiated this cost-effective catalytic system from the classic Lewis acids.