Abstract
Base-catalyzed decomposition of cyclic peroxy ketals lc, 2c, 14, and 16 shows a strong stereochemical dependence. Isomers 2c and 16 with a pseudoequatorial hydrogen undergo a fast antiperiplanar E2 elimination to afford ene diones 4 and 17 that react further. Ester lc, with a pseudoaxial hydrogen
andapseudoequatorialacetatesidechain,reactsslowlytoformtheenolate,whichundergoesan Sn2 reaction to give epoxide 3. Peroxy ketals 14 and 15 are stable in base. Peroxy acetals 19 and 20 undergo a faster E2 elimination with loss of the pseudoequatorial acetal proton to provide alkoxide ester 21 that reacts further.