Organoboranes. 31. A simple preparation of boronic esters from organolithium reagents and selected trialkoxyboranes

Article abstract of DOI:10.1021/om50004a009

The reaction of methyllithium with trimethoxyborane at -78°C in ethyl ether yields a mixture of methylated boranes and their corresponding ate complexes. We have found that under the same conditions triisopropoxyborane reacts cleanly with methyllithium to form the lithium methyltriisopropoxyborate complex. Protonation of this complex with anhydrous hydrogen chloride quantitatively yields methyl diisopropoxyborane. This reaction of organolithium reagent with triisopropoxyborane appears to provide a general, valuable route to boronic esters. Other alkoxyboranes were examined for their selectivity for monomethylation by methyllithium. In addition to triisopropoxyborane, triisobutoxyborane and tri-sec-butoxyborane also give the methylboronic esters quantitatively. This development provides the first general preparation of boronic esters from organolithium reagents.