Convenient Method for the Preparation of 1-Phenylthio-3-alken-1-ynes and 4-Hydroxy-1-phenylthio-1,2-alkadienes from a Common Precursor.

4-Hydroxy-1-phenylthio-2-alkynes (5) reacted with dihydropyran to afford the corresponding 4-tetrahydropyranyloxy derivatives which, on treatment with KHMDS, gave a mixture of (E)- and (Z)-1-phenylthio-3-alken-1-ynes, with the former predominant. When MeLi was used in the place of KHMDS, the (Z)-isomers were formed in preference to the (E)-isomers. Further treatment of the mixture with a base converted the (Z)-isomers into (E)-isomers. On the other hand, the reaction of 5 with KHMDS gave the corresponding 4-hydroxy-1-phenythio-1,2-alkadienes.