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

Abstract

Photoinduced electron transfer reactions of the title N-acyl-α-dehydronaphthylalaninamides [ ( Z)- 1 ] 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 ( 2 ) in excess at rt, respectively. The magnitude of diastereomeric excess (de) was varied in the range of −5–26% for ( R, S)- 2 and 16–92% for ( S, S)- 2 , depending on the chiral auxiliary and reaction temperature. The mechanism of asymmetric induction in the photocyclization process eventually affording diastereomeric 2 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.