Syntheses involving alkylation of organoboranes

A modified version of this reaction utilizes cyclic trialkylboron compounds (borinanes if the ring is six-membered). These are made by reacting diborane first with a diene and then with the alkyl group that is to be synthetically elaborated  

A second means of effecting alkylations of organoboranes involves reactions with highly reactive alkyl halides, especially a-halocarbonyl compounds. For example, ethyl bromoacetate has been found to alkylate a number of trialkylboranes in excellent yield. This synthetic transformation is more efficiently carried out using a 

The mechanism by which these alkylations occur is fundamentally similar to the oxidation of organoboranes to alcohols. It is believed that the enolate of the haloester or haloketone reacts with the borane. Subsequently, elimination of halide, followed by migration of one of the boron substituents, occurs. In agreement with this mechanism, retention of configuration of the migrating group is observed.  

A closely related reaction employs a-diazoesters or a-diazoketones. 

Molecular nitrogen then acts as the leaving group in the migration step. The best results are achieved with dialkylchloroboranes or alkyldichloroboranes.  

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