Highly Diastereoselective Synthesis of<i>cis</i>-2,3-Disubstituted γ-Lactones by the Reaction of 2,2-Dialkoxy-3-alkylcyclopropanecarboxylic Esters with Symmetric Ketones
In the presence of titanium(IV) chloride, 2,2-dialkoxy-3-alkylcyclopropanecarboxylic esters reacted with symmetric ketones to give cis-2,3-disubstituted γ-lactones with high diastereoselectivity. The resulting cis-lactones were easily converted into trans-isomers by treatment with a catalytic amount of sodium ethoxide.