Calciferol and its relatives. Part XII. (S)-3-ethynyl-4-methylcyclohex-3-en-1-ol

Abstract

1-Ethynyl-2-methylcyclohex-1-ene, hitherto obtained only as a mixture with one of its double-bond isomers, is obtained pure by dehydrohalogenation of ω-halogenodienes such as 1-(2-chlorovinyl)-2-methylcyclohexene (6; X = Cl). The optically active 5-hydroxy-2-methylcyclohex-1-enecarbaldehyde (10) reacts with chloromethylenetriphenylphosphorane giving mixed cis- and trans-ω-chloro-dienes [cf.(11)], dehydrohalogenation of which gives the title compound (12), required for the synthesis of precalciferol₃.