A new synthesis of an α-haloalkaneboronic ester, 1-bromo-1-ethylenedioxyboryl-2-phenylethane, and a supervenient synthesis of a 1,2-diboronic ester. 1,2-bis(ethylenedioxyboryl)-1-phenylethane

Abstract

Conversion of tris(ethylenedioxyboryl) methane, HC(BO 2-C 2H 4) 3 (I) to lithium bis(ethylenedioxyboryl)methide, Li HC(BO 2C 2H 4) 2 (II), with methyllithium, followed by alkylation with benzyl bromide, has yielded 1,1-bis(ethylenedioxyboryl)-2-phenylethane, PhCH 2CH(BO 2C 2H 2) 4 (III). Reaction of III with one equivalent each of mercuric chloride and sodium methoxide in anhydrous methanol resulted in the selective replacement of one boron atom by mercury to form 1-chloromercuri-1-ethylenedioxyboryl-2-phenylethane (IV), which reacted with bromine in dichloromethane to yield 1-bromo-l-ethylenedioxyboryl-2-phenylethane, PhCH 2CHBrBO 2C 2H 4 (V). Several attempts to convert V to an aminoboronic acid were unsuccessful. In an attempt to find a more convenient route to III, the dihydroboration of phenylacetylene with borane in tetrahydrofuran followed by treatment with ethylene glycol unexpectedly yielded not III, but its isomer 1,2-bis(ethylenedioxyboryl)-1-phenylethane (VI), which is consequently the first 1,2-alkanediboronic ester to be easily made in substantial quantities.