[4+2]CYCLO ADDITION OF DIPHENYLKETENE TO 1-AZA-1,3-DIENES

摘要

On heating 3-cyano-1-aza-1,3-dienes 5,6 and 9 with diphenylketene,[4+2]cycloaddition took place smoothly to afford the corresponding piperidin-2-one derivatives 7,8 and 10 in high yields,respectively.The Diels-Alder reaction of 1-aza-1,3-dienes 1 with various dienophiles is a useful synthetic tool for six-inembered ring systems containing nitrogen atoms.On using ketenes as dienophiles,the Diels-Alder reaction of 1 appears to directly provide piperidin-2-ones 2;however,this reaction suffers competitive[2+2]cycloaddition of ketenes to imines on 1 to afford beta-lactams 3.