A convenient solution and solid-phase synthesis of Δ5-2-oxopiperazines via N-acyliminium ions cyclization

An extremely efficient synthesis of Delta(5)-2-oxopiperazines in solution phase and on solid support has been established via a Ugi four-component condensation reaction (U-4CC) followed by N-acyliminium ion cyclization between the aldehyde (acetal) functionality and the newly formed amide bond. The desired Delta(5)-2-oxopiperazines are obtained in excellent yields and purity. (C) 2002 Elsevier Science Ltd. All rights reserved.