Abstract
Five- and six-membered ring systems containing a nitrogen atom at the bridgehead position were prepared via [3+2] dipolar cycloaddition of 1-pyrroline 1-oxide (5) with 2-aryl-3-butenoates. Cycloaddition of 5 with methyl 4, 4-dichloro-2-[4-(tosyloxy) phenyl]-3-butenoate (4) gave 3 (and 2)-dichloromethyl-2 (and 3)-methoxycarbonyl-2 (and 3)-[4-(tosyloxy) phenyl]-2, 3, 3a, 4, 5, 6-hexahydropyrrolo [1, 2-b] isoxazole (6 and 7) in a ratio of 52 : 10. Compound 6 was converted to 1-aza-3-r-hydroxy-4-c-methyl-3-t-[4-(tosyloxy) phenyl] bicyclo [3.3.0] octan-2-one (12) by treatment with zinc in aqueous acetic acid in one step or via the 4-chloromethyl analog of 12 (i.e., 11). On the other hand, cycloaddition of 5 with methyl 2-phenyl-3-butenoate (15) afforded methyl 2, 3, 3aα, 4, 5, 6-hexahydropyrrolo [1, 2-b] isoxazol-2α-yl phenyl acetate (16) and 2-methoxycarbonyl-3-methyl-2-phenyl-2, 3, 3a, 4, 5, 6-hexahydropyrrolo [1, 2-b] isoxazole (17) and its regioisomer (18) in a ratio fo 17 : 31 : 32. Treatment of 16 with zinc in aqueous acetic acid furnished 1-aza-4β-hydroxy-3α-phenyl-5aαH-bicyclo [4.3.0] nonan-2-one (20).
