SYNTHESIS OF -TRIMETHYL-6,10-DIOXASPIRO[4.5]DEC-2-ENE-1-ETHANOL - X-RAY CRYSTALLOGRAPHY OF THYL-1-(PROP-2'-ENYL)-6,10-DIOXASPIRO[4.5]DEC-2-YL BENZOATE

Reaction of 2-methyl-2-(prop-2'-enyl)cyclopentane-1,3-dione (2) with 2 ,2-dimethylpropane-1,3-diol gave l-1-(prop-2'-enyl)-6,10-dioxaspiro[4. 5]decan-2-one (3), hydride reduction of which afforded a 1:1 epimeric mixture of the corresponding alcohols (4a) and (4b). They were separat ed, and the derived benzoates (5a) and (5b) were each subjected to a t hree-step sequence of oxidative cleavage, borohydride reduction and si lylation to give the pure epimers (8a) and (8b) of imethylsilyloxyethy l)-6,10-dioxaspiro[4.5]dec-2-yl benzoate. Flash vacuum pyrolysis of a mixture of these epimeric benzoates (8a,b) gave an almost quantitative yield of methylsilyloxyethyl)-6,10-dioxaspiro[4.5]dec-2-ene (9a), tre atment of which with tetrabutylammonium fluoride afforded the correspo nding alcohol (9b). The relative stereochemistry of thyl-1-(prop-2',en yl)-6,10-dioxaspiro[4.5]dec-2-yl benzoate (5b) was established by X-ra y crystallography.