Base-promoted thioannulation of o-alkynyl oxime ethers with sodium sulfide for the general synthesis of isothiocoumarins.

A general and facile strategy for the synthesis of isothiocoumarin-1-ones has been developed via the base-promoted 6-endo-dig thioannulation of o-alkynyl oxime ethers using the cheap and readily available Na2S as the sulfur source in one-pot reactions. Control experiments demonstrated that the reaction proceeded through two C-S bonds formations, N-O bond cleavage and the hydrolysis of imines.