Highly Selective Formation and Ring Fission of Some Cyclobutaquinolizidinones and Cyclobutaindolizidinones.

Intramolecular photochemical cycloaddition in N-alkenoyldihydropydinones or 3-acetyl-N-alkenoyltetrahydropydines is highly diastereoselective and affords substituted Cyclobutaquinolizidinones and cyclobutaindolizidinones, suitable derivatives of which undergo highly regioselective radical ring opening of the cyclobutane ring.