The keto sulphides (I) were prepared in good yield (72-99x) by base catalysed addition of arylmercaptans to methyl vinyl ketone (MVK) or by interaction of arylmercaptans with Mannich bases derived from ketones. Cyclodehydration of the keto sulphides (I) by interaction with PPA was expected to yield thiachromenes (II). However instead of the latter, thiachromans (III) Qield =p 35%) and t~~aphthaleni~ salts (which subsequently change in suitable cases to t~acya~ne dyes) ...