Trialkylboranes with.ethyl bromoacetate

Carboethoxymethylation. As in the carbonylation reaction cited above, the original two-carbon-atom homologation reaction of trialkylboranes with ethyl bromoacetate (2, 192-193) had the defect that only one alkyl group of the tri-alkylborane is utilized. This disadvantage has now been eliminated by use of 9-BBN as the hydroboration reagent. Thus the B-alkyl-9-borabicyclo[3.3.1] nonane (B-R-9-BBN, 2), prepared as above, reacts with ethyl bromoacetate under the influence of potassium f-butoxide to give the homologated ester (3) in... 

Trialkylboranes react with ethyl bromoacetate to give ethyl alkylacetates in good yields (6). As in other reactions of boranes, only one of the three alkyl groups is utilized... 

Conversion of olefins into esters. Brown1 has extended the one-carbon homologation of olefins with carbon monoxide and the three-carbon homologation of olefins with acrolein to a two-carbon homologation with ethyl bromoacetate. The olefin is converted into the trialkylborane in THF at 0° by addition of the calculated quantity of diborane in THF. An equimolecular quantity of ethyl bromoacetate is added, followed by an equimolecular quantity of potassium f-butoxide in t-butanol. The reaction is apparently complete immediately. Ethyl chloroacetate can also be used, but the reaction is somewhat slower and gives slightly lower yields. 

The new base is also superior to potassium /-butoxide for the reaction of organoboranes with ethyl bromoacetate (2, 192-193) and with ethyl dibromo-acetate (2, 195).6 Yields are higher and it is not necessary to avoid an excess of the base. In the case of trialkylboranes the usual reaction conditions were used. For an unknown reason the reaction with B-alkyl-9-borabicyclo[3.3.1]nonanes in THF was unsuccessful. However, if the reaction is carried out in a solution roughly 50 50 in THF and /-butanol, satisfactory yields are obtained. 

Homologation via a-Haloenolates. Organoboranes can also be used to construct carbon-carbon bonds by several other types of reactions that involve migration of a boron substituent to carbon. One such reaction involves a-halocarbonyl compounds.19 For example, ethyl bromoacetate reacts with trialkylboranes in the presence of base to give alkylated acetic acid derivatives in excellent yield. The reaction is most efficiently carried out with a 9-BBN derivative. These reactions can also be effected with B-alkenyl derivatives of 9-BBN to give /i,y-unsaturatcd esters.20... 

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... 

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