DIASTEREOSELECTIVE CYCLIZATION REACTIONS OF CHIRAL PROLINE AUXILIARY-SUBSTITUTED N-BENZOYL-α-DEHYDRO(1-NAPHTHYL)ALANINAMIDE DERIVATIVES VIA PHOTOINDUCED ELECTRON TRANSFER

摘要

Irradiation of the title 1-naphthylalaninamide derivatives [(Z)-1] bearing N'-substituted (S)-prolinamide auxiliaries in 1,2-dichloroethane and methanol containing triethylamine mainly afforded the corresponding (4S,5S). 4,5-dihydrooxazoles [(4S,5S)-2, diastereomeric excess (de) = 21-84%] and (4R,5R)-2 (de = 18-43%), respectively. Analysis of substituent and solvent effects on the diastereoselective photocyclization of (Z)-l substantiated that steric bulkiness of the chiral auxiliary, solvent polarity, and intramolecular hydrogen bond are major factors controlling de, while intermolecular hydrogen-bonding and charge-transfer interactions invert the configuration of the dihydrooxazole diastereomer preferentially formed.