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.
Diastereoselective ring-opening aldol-type reaction of 2,2-dialkoxycyclopropanecarboxylic esters with carbonyl compounds. 2. Synthesis of cis-2,3-substituted-γ-lactones
The reaction of 3-alkyl-2,2-dialkoxycyclopropanecarboxylic esters 1d–i with symmetrical ketones and formaldehyde was investigated. Cyclopropanes 1d–i react with symmetrical ketones and formaldehyde in the presence of TiCl4 to give cis-2,3-substituted-γ-lactones in good yields with high diastereoselectivity. In the reaction of 3-ethylcyclopropane 1d, the reaction conditions hardly influenced the diastereoselectivity