An Efficient Transformation of Substituted N-Acyl-a-dehydro(1-naphthyl)alanines into 1,2-Dihydrobenzo[f]quinolinone Derivatives via Photoinduced Intramolecular Electron Transfer

The irradiation of substituted (Z)-N-acyl-α-dehydro(1-naphthyl)alanines(1) having the dialkylamino donor on the carboxamide side chain in methanol was found to give 1,2-dihydrobenzo[f]quinolinone derivatives (2) in good yields, which were formed via the electron-transfer reaction in the excited-state (E)-isomers, while intramolecular photocyclization reactions in the (Z)-and (E)-isomers afforded minor amounts of benzo[f]isoquinolines (3) and 1-azetines (4), respectively.The replacement of the N-acetyl group by the benzoyl (having stronger electronwithdrawing ability and larger steric bulkiness than the former) increased the selectivity for 2 and 4, and this increased selectivity was mainly reflected in a great lowering of that for 3.