Aldehyde to Ketone Homologation Enabled by Improved Access to Thioalkyl Phosphonium Salts.

Phosphines were previously unusable as Pummerer-type nucleophiles due to competing redox chemistry with sulfoxides. Here we circumvent this problem to achieve a formal phosphine Pummerer reaction that offers thioalkyl phosphonium salts that, in turn, give rise to diverse vinyl sulfides via Wittig olefinations. Thirty vinyl sulfides are thus prepared from (alkylthioalkyl)triphenyl phosphonium salts and aldehydes. The hydrolysis of these vinyl sulfides offers an efficient and versatile two-step one-carbon homologation of aldehydes to ketones.