Calciferol and its relatives. Part 21. A synthesis of (S)-(Z)-2-(5-hydroxy-2-methylenecyclohexylidene)ethanol

Abstract

The paper describes experiments on the synthesis of the title compound, which is of interest as a ring A intermediate for a synthesis of the vitamins D. The primary α-phenylthioacetate of (±)-4-hydroxycyclohex-1-enemethanol was protected and subjected to Claisen rearrangement to give mixed α-phenylthio-γδ-unsaturated acids which were converted into iodo-lactones and, after oxidation, into sulphoxides, which were thermolysed to provide δ-iodo-αβ-unsaturated γ-lactones; these were then converted into the racemic form rac-(27) of the title compound.

In a second (perferred) route, (+)-cyclohex-4-ene-1, trans-2-dimethanol (29) was first converted by standard methods into (1S,5R)-6-methylene-2-oxabicyclo[3.3.1]nonan-3-one (36) and then into the diol (43), from which the synthesis of the optically active compound (27) was completed by a sulphoxide thermolysis.