US 92317497 A description in a preferred embodiment 4r 4 u03b1 5 u03b2 4 5 dicyclohexyl 2 methyl 1 3 2 dioxaborolane 6 and dichloromethyl lithium react to yield 4r 2 s 4 u03b1 5 u03b2 4 5 dicyclohexyl 2 1 chloroethyl 1 3 2 dioxaborolane 7 this reaction is known to occur in two stages and the second stage is promoted by zinc chloride matteson d s and sadhu k m u s pat no 4 525 309 jun 25 1985 matteson d s et al j am chem soc 1986 108 812 819 reaction of 7 with 1 buten 2 yl magnesium bromide 8a yields 4r 2 r 4 u03b1 5 u03b2 4 5 dicyclohexyl 2 2 ethyl 3 methylpropen 3 yl 1 3 2 dioxaborolane 9a the overall process of converting a boronic ester of a diol of c 2 symmetry i e a 4 u03b1 5 u03b2 4 5 dialkyl 2 alkyl 1 3 2 dioxaborolane to a chloro boronic ester using the reaction with dichloro methyl lithium followed by replacement of the chloride with an alkyl group from a grignard or lithium reagent is known to yield a single diastereoisomer of gt 99 purity in several instances tripathy p b and matteson d s synthesis.