Synthesis of 1H-[1]Benzothieno[3,2-d]azonine and [1]Benzothieno[3,2-d]azecine Derivatives

Abstract

Derivatives of two new [1] benzothieno medium-ring heterocyclic systems have been prepared by ring degradation using cyanogen bromide-induced solvolysis of tetracyclic precursors. Reaction of a hexahydro -[1] benzothieno [3,2-g] indolizine (4a) and a hexahydro-2H-[1] benzo-thieno [2,3-a] quinolizine (4b) with cyanogen bromide and magnesium oxide under solvolytic conditions yielded the hexahydro-1H-[1] benzothieno [3,2-d] azonines (5a) and (6a) and the octahydro -[1] benzothieno [3,2-d] azecines (5b) and (6b), respectively. Functional group interconversions of these medium-ring systems are described, including oxidations to the cyclic ketones (7) and (9). The 11b-phenyl derivative (13) of (4a) reacted under similar conditions to give both solvolysis (14) and (16) and elimination (15) medium-ring products, the ratios depending on the solvent. By contrast the analogous 9a-phenylthienoindolizine derivative (17) under these conditions gave only the medium-ring elimination product (18) in aqueous medium, and only the equivalent solvolysis product in methanol. Both the thieno and [1] benzothienoazonine elimination products (18) and (15) appear to be mixtures of E and Z isomers. The [1] benzothieno [3,2-g] indolizine bases (4a) and (13) are the first reported examples of this ring system.