Cross-linked poly-(4-vinylpyridine–styrene)–bromine complexes as stereoselective brominating agents

Abstract

Cross-linked poly(styrene–4-vinylpyridine) beads, containing 40–43% of pyridine rings, were transformed with bromine to provide three types of brominating agents (1), (2), and (3). Reactions of cis- and trans-1-phenylpropene with (1), (2), and (3) resulted in a high degree of anti-stereoselectivity. The reactivity increases from (1) to (3); solvent polarity has no significant effect on stereoselectivity, but affects the reactivity, being significantly greater in acetonitrile and chloroform than in cyclohexane and dioxan. Bromination of 1-phenylcyclohexene with (1) and (3) resulted in the formation of trans-1,2-dibromo-1-phenylcyclohexane (9) and 3-bromo-2-phenylcyclohexene (10), the temperature affecting only the ratio of the products. Bromination of norbornene with the reagents (1), (2), and (3) resulted in the formation of seven products: 2-exo-bromonorbornane (12), 7-bromonortricyclane (13), 2-exo, 3-endo-dibromonorbornane (14), 2-exo-7-anti-dibromonorbornane (15), 2-exo, 5-endo-dibromonorbornane (16), 2-exo, 5-exo-dibromonorbornane (17), and 2-exo, 7-syn-dibromonorbornane (18).