Gabbutt, Christopher D., Hepworth, John D., Heron, B. Mark, Coles, Simon J. and Hursthouse, Michael B. (2000) Synthesis of some thiochromeno[4,3-c]- and [3,4-c]-pyrazoles. Journal of the Chemical Society, Perkin Transactions 1 (17). pp. 2930-2938. ISSN 1470-4358

Reaction of 3-hydroxymethylene- and 3-cyanomethylene-thiochroman-4-ones with various hydrazine derivatives affords 4H-thiochromeno[4,3-c]pyrazoles. The novel isomeric thiochromeno[3,4-c]pyrazoles result when 4-(dimethylaminomethylene)thiochroman-3-ones react with methyl- and phenyl-hydrazines. Acidic hydrolysis of 3-(dimethylhydrazonoethylidene)-2,2,6-trimethylthiochroman-4-one yields the 3-cyanomethylenethiochroman-4-one. Formation of 6-chloro-3-hydroxymethylenethiochroman-4-one is accompanied by a thiochroman-3-yl(oxothiochromen-3-yl)methane derivative produced through a rearrangement–carbocation interception sequence. A 3-isopropenylthiochromenone, obtained by the acid promoted rearrangement of a 3-hydroxymethylenethiochroman-4-one, undergoes Diels–Alder cycloadditions to provide a new route to thioxanthenones.

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