A NOVEL SYNTHESIS OF SPIRO 1,3-DITHIIN AND SPIRO 1,3-THIAZINE DERIVATIVES UNDER PHASE TRANSFER CATALYSIS (PTC) CONDITIONS

Ketene S,S-acetals 1a, b or ketene N,S-acetals 2a, b reacts in situ with a variety of ylidenemalononitriles to afford the desired spiro [1,3]dithiin heterocycles 3a, b–11a, b or spiro[1,3]thiazine heterocycles 12a, b–20a, b. Treatment of 2-(1-acetyl-2-oxopropylidene)spiro[1,3]thiazine derivatives 13b, 17d, and 18d with malononitrile afforded the corresponding dispiro heterocycles 21, 22, and 23.