Stereoselective intra- and intermolecular [2+2] photocycloaddition reactions of 4-(2′-aminoethyl)quinolones

The 4-(2′-aminoethyl)quinolones 6, 8 and 9 were prepared starting from 4-(2′-bromoethyl)quinolone (4) in two steps and overall yields of 56-93%. They underwent inter- and intramolecular [2+2] photocycloaddition reactions with an alkene to provide the cyclobutanes 1-3 in racemic form (61-89% yield). The photochemical reaction proceeded with very good chemo-, regio- and stereo-selectivity. It was in one case (8b → 2b) also performed enantioselectively (93% ee).