A novel [3+2] type reaction of 2,2-dialkoxycyclopropanecarboxylic esters with ketene silyl acetals, mediated by titanium(IV) chloride, afforded 3-alkoxy-2- (or -3-) cyclopentenone derivatives.
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