Stereoselective synthesis of 4-alkylidene pyrrolidinones and pyrrolizidinones

Article abstract of DOI:10.1016/S0040-4039(99)00673-5

α-Aminoalkylcuprates prepared from tert-butoxycarbonyl protected amines undergo a conjugate addition reaction with α,β-β,γ-allenyl esters to afford the corresponding β,γ-unsaturated esters with a high degree of stereoselectivity. Treatment of the unsaturated esters with PhOH/TMSCl or catechol boron bromide effects amine deprotection and lactamization to afford a 4-alkylidene-2-pyrrolidinone ring with preservation of the original olefin stereochemistry. The method can be used to prepare 4-alkylidene 2- pyrrolidinones and 2-pyrrolizidinones.