Process for the preparation of 4,4-dimethyl-6-ethynylthiochroman

An improved process for the preparation of key intermediates for tazarotene, 4,4-dimethyl-6-ethynylthiochroman, is provided comprising (a) reacting 4,4-dimethyl-6-acetylthiochroman of the formula with an acid chloride and an amido-group containing compound of the general formula wherein R is hydrogen or a hydrocarbyl of from 1 to 15 carbon atoms and R1 and R2 can be the same or different and are hydrocarbyls of from 1 to 15 carbon atoms or R1 and R2 together with the nitrogen atom to which they are bonded are joined together to form a heterocyclic group, optionally containing one or more additional heterocyclic atoms, or one of R1 and R2 together with the nitrogen atom to which it bonded are joined together with the carbonyl radical to form a heterocyclic group, optionally containing one or more additional heterocyclic atoms to form a beta-chloro vinyl carbonyl compound intermediate of the general formula wherein R has the aforestated meanings; and (b) reacting the beta-chloro vinyl carbonyl compound intermediate with an alkali metal to provide the 4,4-dimethyl-6-ethynylthiochroman.