Solvent-Free Cyclocondensation of Lactim Ethers with Anthranilic Acid under Microwave Irradiation

Abstract Microwave irradiation greatly improves the results of the cyclocondensation between anthranilic acid and lactim ethers derived from 2,5-piperazinediones in terms of reaction times, yields and stereocenter integrity, leading to pyrazino[2,1-B]quinazoline-3,6-diones. The microwave-assisted reaction was also much better than the thermal one when applied to a bis-lactim ether, leading to the corresponding pentacyclic pyrazino [2,1-B:5,4-B′]diquinazol­ine-5,13-dione in excellent yield, and it also improved the preparation of compounds containing the ring system of the anti-MDR natural product N-acetylardeemin.