Synthesis of Saturated and Aromatic Ketones

Excellent yields of the ketones are achieved from internal alkynes (Eq. 7.5 Table 7.8) [1] via hydroboration with 1 equiv of 9-BBN. The boron of 9-BBN adds to the less hindered carbon of carbon-carbon triple bond, and oxidation of the resulting B-alkenyl-9-BBN affords the corresponding ketones. 

Tabl yji Directive effects in the hydroboration of methyl-substituted alkynes by 9-BBN [1] 

These studies also show that 9-BBN is not only most sensitive to the steric environment, but it is also most sensitive to the electronic environment [1]. 

The homologated ketones are synthesized by adding the a-bromoketone and potassium f-butoxide simultaneously to the B-R-9-BBN at 0 °C. This simultaneous addition procedure provides good yields of the desired ketone with an additional alkyl group (Chart 7.3) [2a], 

The B-alkyl-9-BBN and B-aryl-9-BBN not available via hydroboration undergo reactions with ethyl haloacetates and a-bromoketones. The reaction sequence provides a convenient procedure for the a-arylation of ketones and esters under the influence of potassium f-butoxide (Eq. 7.6 Table 7.10) [2b]. 

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