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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. |
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