Electron transfer-initiated asymmetric photocyclization of chiral auxiliary-substituted N-acyl-α-dehydro(1-naphthyl)alaninamides to the corresponding 3,4-dihydrobenzo[f]quinolinone derivatives

Photoinduced electron transfer reactions of the title N-acyl-α-dehydronaphthylalaninamides [] with (S)-1-phenylethylamino and (S)-alaninamide auxiliary groups in methanol containing a tertiary amine were shown to form (R,S)- and (S,S)-3,4-dihydrobenzo[f]quinolinone derivatives () in excess at rt, respectively. The magnitude of diastereomeric excess (de) was varied in the range of −5–26% for and 16–92% for , depending on the chiral auxiliary and reaction temperature. The mechanism of asymmetric induction in the photocyclization process eventually affording diastereomeric was discussed based on solvent, tertiary amine, chiral auxiliary and temperature effects on the de value as well as on MM2 and PM5 calculations for the diastereomeric enol intermediates.