Novel syntheses of hexahydro-1H-pyrrolo[1,2-a]imidazoles and octahydroimidazo[1,2-a]pyridines

1-Phenyl-5-(benzotriazol-1-yl)hexahydro-1H-pyrrolo[1,2-a]imidazole (18) and 1-phenyl-5-benzotriazolyloctahydroimidazo[1,2-a]pyridine (27) were readily prepared from succindialdehyde or glutaraldehyde, benzotriazole, and N-phenylethylenediamine. Synthons 18 and 27 reacted with Grignard reagents, allylsilanes, silyl ethers, and triethyl phosphite to produce 1-phenyl-5-substituted-hexahydro-1H-pyrrolo[1,2-a]imidazoles 20a-f, 22, 24a,b, and 25 and 1-phenyl-5-substituted-octahydroimidazo[1,2-a]pyridines 28a-e, 32, 33a,b, and 34 in good to excellent yields. The configurations of 20, 22, 24, and 25 were determined to be cis isomers by NOE experiment, while the configurations and conformations of 28a-e, 32, 33a,b, and 34 were elucidated by H-1-H-1 COSY and H-1-C-13 COSY.