Enolic Ortho Esters. III. Preparation of a Keto Acetal by Hydride Reduction of an Enolic Ortho Ester

Abstract

Lithium aluminium hydride reduction of the enolic ortho ester 4′,4′-dimethyl-3,4,5,8-tetra-hydrospiro [2H^-l-benzopyran-2,2₁-[1,3]dioxolan] (8) in the absence of solvent gave 6-[2₁-(4″,4″- dimethyl-1″,3″-dioxolan-2″-yl)ethyl]cyclohex-3-en-1-one (11) which was isomerized to the α'β-unsaturated keto acetal (10). Similarly, hydride reduction of the phenolic ortho ester 4′-methyl-3,4-dihydrospiro[2H-1-benzopyran-2,2′-[1,3]dioxolan] (12a) and the 4′,4′-dimethyl analogue (12b), afforded the corresponding phenolic acetals (14a) and (14b) respectively, in high yields.′