The insertion and extrusion of heterosulfur bridges. XV . S ‐bridging of 2,2′‐binaphthyl and 1‐(2‐naphthyl)cyclohexene. Studies on hydrodehalogenation during the reaction

Regioselectivity occurs in the sulfur‐bridging reactions of 2,2′‐binaphthyl (1) and 1‐(2‐naphthyl)cyclohexene (7) by means of hydrogen sulfide and a chromia‐alumina‐magnesia catalyst (designated I) in a flow apparatus at 550°. Thus, 1 gives a higher yield (6.1%) of dinaphtho[1,2–6:2′,l'‐ d ]thiophene from 1,1′‐bridging than of dinaphtho[1,2‐ b :2′,3′‐ d ]thiophene (3.4%) from l,3′‐bridging. No product expected from 3,3′‐bridging was identified. Substrate 7 undergoes both dehydrogenation and bridging to yield 2‐phenylnaphthalene (8%), benzo[ b ]naphtho[2,1‐ d ]thiophene (9%) from alpha bridging, and benzo[ b ]naphtho[2,3‐ d ]thiophene (3%) from beta bridging into the naphthalene ring. Exploratory studies showed that either sulfided catalyst I or a sulfided molybdenum( VI ) oxide‐alumina‐cobalt( II ) oxide catalyst ( II ) effects hydrodehalogenation of various monohalo‐ and polyhaloarenes (where halo, X, is chloro or bromo) at 450–550°. In the biphenyl, phenanthrene, naphthalene, and pyrene systems, halogen was lost either under sulfur‐bridging conditions or under hydrogenolysis conditions, i.e. with methanol as a reactant. For every substrate the parent arene was isolated or identified as a reaction product. In selected experiments, acid HX was also identified in the effluent. Use of hydrogen sulfide as a reactant led to formation of dibenzothiophene and phenanthro[4,5‐ bcd ]thiophene as main products in the biphenyl and phenanthrene systems, respectively; while use of methanol as a reactant gave small amounts of methyl bromide (for X = Br) and methylarenes.