Novel syntheses of camptothecin alkaloids. Part I. Intramolecular [4 + 2] cycloadditions of N-arylimidates and 4H-3,1-benzoxazin-4-ones as 2-aza-1,3-dienes

Article abstract of DOI:10.1016/0040-4039(96)01204-X

The first reported intramolecular [4 + 2] cycloadditions of both N-arylimidates and 4H-3,1-benzoxazin-4-ones acting as 2-aza-1,3-dienes are described. Reaction with unactivated alkynes leads to pyrrolo[3,4-b]quinolines which constitute the ABC ring system of camptothecins.