10-Phenyl-4,5,6,7,8,10-hexahydrothieno[3,2-g][1,4]oxazonine-6-carbonitrile (6a) and 11-phenyl-4,6,7,8,9,11-hexahydro-5H-thieno[3,2-h][1,5]oxazecine-6-carbonitrile (7a) were prepared in moderate yields by cyanogen bromide-induced ring expansion of tetrahydrothieno [2,3- c] pyridinylalkanol precursors (4a) and (5a), respectively. 1-Phenyl-1,3,4,5,6,7-hexahydro[1]- benzothieno [3,2-g][1,4]oxazonine-5-carbonitrile (6b) and 1-phenyl-3,4,5,6,7,8-hexahydro-1H- [1] benzothieno [3,2-h][1,5]oxazecine-6-carbonitrie (7b) were similarly prepared from the [1] benzothieno [2,3-c] pyridinylalkanol precursors (4b) and (5b). The medium-ring cyanamides (6b) and (7b) were converted by standard methods into their N-methyl analogues (8b) and (9b). 6-Methyl-8-phenyl-4,5,6,8-tetrahydrothieno[3,2-e][1,2] oxazepine (13) was prepared by thermal Meisenheimer rearrangement of the corresponding tertiary amine N-oxide (12). The compounds (6a, b), (7a, b) and (13) are each the first reported examples of new heterocyclic systems. The crystal and molecular structure of (6b) has been determined by X-ray crystallographic methods.