C-H functionalization of terminal alkynes towards stereospecific synthesis of (E) or (Z) 2-methylthio-1,4-ene-diones.

An efficient metal free self-sorting tandem protocol for stereospecific synthesis of 2-thio-1,4-enediones involving C-C double bond formation via direct coupling of terminal alkynes has been developed. The method was also extended to the first synthesis of β-thio-γ-keto-α,β-unsaturated esters via a cross coupling reaction with ethyl glyoxylate. The reaction relies on a first of its kind use of Bronsted and Lewis acids to switch selectivity for the synthesis of an E or a Z-isomer respectively.