Metal-free synthesis of E-vinylphosphonates via photoinduced alkyne hydrophosphonylation and thiol promoted isomerization sequence

The alkyne hydrophosphonylation is an atom economical method for the synthesis of vinylphosphonates that are compounds of both biological and synthetic relevance. Recent approaches based on the use of metal catalysts have only partially solved the problems of the reaction selectivity as well as of economical and large amount production. We report in this Letter on a metal-free approach that leads to E-vinylphosphonates in high yields. The approach is based on a two-step one-pot synthesis, namely: (a) photoinduced anti-Markovnikov addition of a H-phosphonate to alkynes to give mixtures of E- and Z-vinylphosphonates, and (b) cysteine promoted photoinduced conversion of the crude mixtures of adducts into E-isomers (58-92% overall yields).