Homochiral ketals in organic synthesis. Diastereoselective cyclopropanation of α,β-unsaturated ketals derived from 1,4-D1-O-benzyl-l-threitol

2-Cycloalken-1-one 1,4-di -O-benzyl -L-threitol ketals undergo efficient and diastereoselective cyclopropanation when treated with an excess of the Simmons-Smith reagent. For example, 2-cyclohexen-1-one 1,4-di -O-benzyl -L-threitol ketal gave in 90-98% yield a 9:1 mixture of diastereomeric cyclopropanes as established by 62.9 MHz ¹³C NMR spectroscopy and by hydrolysis of the mixture to (1R,6S)-bicyclo[4.1.0] heptan-2-one. Sixteen other examples are presented which demonstrate the generality and predictability of the process for 2-cycloalken-1-one ketals, as wall as an unfortunate lack of diastereoselectivity for α,β-unsaturated 1,4-di-O-benzyl-L-threitol acetals.