Synthesis and Properties of o-Thioquinone Methides Having Ketene Aminal, Ketene Acetal, Ketene Monothioacetal, or Ketene Dithioacetal Group

Reaction of 1,2-benzodithiole-3-thione with N,N′-dialkyl-1,2-ethanedianiine afforded o-thioquinone methides with a ketene aminal group (6) in high yields. Two similar thionaphthoquinone methides were also prepared. o-Thioquinone methide derived from N,N′-dimethyl-o-phenylenediamine was prepared from 3-chloro-1,2-benzodithiol-3-ylium chloride (10). These compounds were found to exist as a monomer of a considerable betaine nature. Reactions of 6a (N,N′-dimethyl derivative) with dimethyl acetylenedicarboxylate and dibenzoylacetylene led to [4+2] adducts. o-Thioquinone methides with a ketene acetal group were obtained from desulfurization of spiro[1,3-benzodioxole-2,3′-[1,2]benzodithiole] with trimethyl phosphite, which are equilibrated with two kinds of aggregates; one is a dimer and the other is a trimer or a higher oligomer. Reactions of 10 with o-mercaptophenol and 1,2-benzenedithiols gave spiro[1,2-benzodithiole-3,2′-[1,3]benzoxathiole] (29) and spiro[1,2-benzodithiole-3,2′-[1,3]benzodithiole] (39 and 40), respectively. o-Thioquinone methide with a ketene monothioacetal group (30) was prepared by desulfurization of 29. The violet compound 30 is equilibrated with a colorless dimer. This o-thioquinone methide reacted with olefins and an acetylene having electron-withdrawing groups to give 1,4-cycloaddition products. Similar desulfurization of 39 and 40 gave o-thioquinone methides with dithioacetal group. Their properties were very similar to those of o-thioquinone methides with dithioacetal group prepared by the photoreaction of 2 with olefins.