Sulfuric Acid → 6-Bromo-2-cyclohexyl-3,4-dihydro-2H-benzopyran

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Reaction Conditions

Reaction Steps

A solution of cyclohexylmagnesium bromide in ethyl ether (55 ml) was prepared from 15.6 g (96 mmole) cyclohexyl bromide and 2.56 g magnesium. This was added dropwise to a solution of 5.5 g (24 mmole) 6-bromo-2chromanol in 55 ml dry tetrahydrofuran, under nitrogen at -70° C. The reaction mixture was stirred at -78° C. for two hours, then at 0° C. for one hour and quenched by addition of 4.1 ml acetic acid. The solvents were evaporated in vacuo, the residual white gel diluted with 250 ml ethyl acetate, washed with 1N hydrochloric acid (100 ml), saturated sodium bicarbonate solution, and dried (Na2SO4). Evaporation of solvent afforded an oil which solidified upon trituration with hexane, 5.3 g, m.p. 124°-126° C. This was identified as the diol, 1-cyclohexyl-3-(2-hydroxy-5-bromophenyl)propanol. The diol was dissolved in 125 ml acetic acid, 2.5 ml concentrated sulfuric acid added and the mixture heated at reflux for 16 hours. After evaporation in vacuo, the residue was diluted with ethyl acetate, washed with saturated sodium bicarbonate, dried (Na2SO4), carbon treated, the solution evaporated and passed through a silica gel column, eluting with hexane to yield 1.45 g of the title compound as an oil. The structure was verified by 1H-NMR spectroscopy.

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