reaction of the sodium α-sulfinyl carbanion of a racemic aryl dichloromethyl sulfoxide to (−)-menthone in the presence of boron trifluoride diethyl etherate gave an adduct as a mixture of two easily separable diastereomers. After separation of the diastereomers, they were each treated with sodium hydride to afford enantiomerically pure aryl dichloromethyl sulfoxides and (−)-menthone both in high yields