Stereochemical Dependence of Base-Catalyzed Cleavage of Cyclic Peroxy Ketals

Article abstract of DOI:10.1021/jo00086a022

Base-catalyzed decomposition of cyclic peroxy ketals 1c, 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 1c, with a pseudoaxial hydrogen and a pseudoequatorial acetate side chain, reacts slowly to form the enolate, which undergoes an S_N2 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.