Diastereoselective Synthesis of Highly Substituted Cyclopentenones

Significance

Highly substituted cyclopentenones (especially at the 5-postion R³/Z) were obtained in moderate to good yield and in good to excellent diastereoselectivity by a formal [4+1] addition. ZnBr₂ was found to be the best Lewis acid for this process to enhance the reactivity of some substrates. A broad range of functional groups was tolerated under the reaction conditions to give the desired product from a trialkylsilyl vinyl ketene and a benzotriazolyl organolithium reagent. The trialkylsilyl group at the 2-position of the cyclopentenone was transformed to the synthetically useful iodo group or reduced to hydrogen.