88765-78-0Relevant academic research and scientific papers
Homologation of boronic esters to α-chloro boronic esters
Matteson, Donald S.,Majumdar, Debesh
, p. 1529 - 1535 (2008/10/08)
The homologation of boronic esters, RBO2C2R′4 (7), with (dichloromethyl)lithium to form α-chloro boronic esters, R-CHCl-BO2C2R′4 (3), has been found to be a highly efficient process. R may be primary, secondary, or tertiary alkyl, cycloalkyl, alkenyl, allyl, aryl, or benzyl, and functional substituents in R may include α-benzyloxy, β or remote carbalkoxy, or a remote ketal substituent. R′ was H or CH3. The homologation failed in the presence of an α-phenylthio or an α-boronic ester substituent. The α-chloro boronic esters readily undergo nucleophilic replacement of chloride with a variety of reagents, including thiophenolate, benzyl oxide, an ester enolate, or alkyl groups from Grignard or lithium reagents. Either 100% C-alkylation or a majority of O-alkylation and Cope rearrangement could be obtained when tert-butyl lithioacetate reacted with pinacol 3-chloro-1-propene-3-boronate. The β-benzyloxy boronic ester (11) obtained by homologation of pinacol 1-(benzyloxy)pentane-1-boronate (10) decomposed slowly by β boron-oxygen elimination above 100°C but was stable enough to permit replacement of the α-chlorine by methylmagnesium bromide to form 12, which was oxidized with sodium perborate to a mixture of diastereomeric 3-(benzyloxy)-2-heptanols (13).
