Pyridine hydrobromide perbromide mediated regioselective heterocyclization of ortho-cyclohexenyl phenols

Abstract

A number of 3,4-benzo-9-bromo-2-oxabicyclo[3.3.1]nonanes (9a–h) are synthesized in almost quantitative yields by regioselective heterocyclization of ortho-cyclohexenyl phenols (8a–h). The structures of 3,4-benzo-9-bromo-2-oxabicyclo[3.3.1]nonane 9 have been unambiguously settled by the synthesis of 9-chloromercuri-3,4-(4′-methoxybenzo)-2-oxabicyclo[3.3.1]nonane 13, which has an X-ray determined structure, and by converting 13 to product 9c with bromine in sunlight in 45% yield. The 6-chloro-2-cyclohexenenyl phenol 8i and 2-cyclohexenyl-4-methyl phenol 8j failed to give any cyclic product but instead furnished the ring-brominated products 10i and 10j, respectively. Keywords: pyridine hydrobromide perbromide, regioselective heterocyclization, ortho-cyclohexenyl phenol, oxabicyclo[3.3.1] nonane, 6-endo trig.