Synthesis and properties of 1-methylthiopropargylammonium salts and their use as key precursors to sulfur-containing enediynes

1-methylthiopropargylammonium salts were synthesized in a highly efficient manner by reaction of alkynyl S,N-acetals with methyl triflate. Reactions of the 1-methylthiopropargylammonium salts with Grignard reagents gave propargyl sulfides or allenyl sulfides, whereas the reaction with organocopper reagents led to exclusive formation of allenyl sulfides regardless of the nature of substituents on the acetylenic carbon. The salts undergo self-dimerization reactions when treated with organolithium and lithium amide bases.