Macrocyclic lactam synthesis via a ring expansion reaction: construction of the cripowellin skeleton.

[reaction: see text] The cripowellin ring skeleton, a macrocyclic [2.3.5]-bicyclic ketolactam, was smoothly generated via construction of a spiro(benzazepin-cyclohexane-1,3-dione) employing oxidative cyclization as a key step and a subsequent ring expansion reaction.