Solvent dependence of the reaction of 1,2-epoxy-1-(p-nitrophenyl)cyclohexane with boron trifluoride–diethyl ether complex

Abstract

The reaction of 1,2-epoxy-1-(p-nitrophenyl)cyclohexane with boron trifluoride–diethyl ether exhibits a pronounced solvent dependence: in benzene it gives a 9 : 1 ratio of cis-2-fluoro-2-(p-nitrophenyl)cyclohexanol to 1-(p-nitrophenyl)cyclopentanecarbaldehyde, which does not change with reaction time; in dichloromethane the cis-fluorohydrin is again the main primary product, but is rapidly converted into the aldehyde in the reaction medium; and in ether about equimolar amounts of cis- and trans-2-fluoro-2-(p-nitrophenyl)cyclohexanol are formed. The presence of small amounts of water in the dichloromethane solvent causes the formation of a ca. 6 : 4 mixture of cis-fluorohydrin and aldehyde, the composition of which changes little with reaction time. This solvent dependence of the reaction can be useful for preparative purposes. A reaction mechanism is suggested.