Diazoketones reaction with boranes

In the late 1960s, methods were developed for the synthesis of alkylated ketones, esters, and amides via the reaction of trialkyl-boranes with a-diazocarbonyl compounds (50,51), halogen-substituted enolates (52), and sulfur ylids (53) (eqs. [33]-[35]). Only one study has addressed the stereochemical aspects of these reactions in detail. Masamune (54) reported that diazoketones 56 (Ri = CH3, CH2Ph, Ph), upon reaction with tributylborane, afford almost exclusively the ( )-enolate, in qualitative agreement with an earlier report by Pasto (55). It was also found that E) - (Z)-enolate isomerization could be accomplished with a catalytic amount of lithium phenoxide (CgHg, 16 hr, 22°C) (54). 

Alkylation.—Position-specific alkylation of ketones can be achieved by a number of new methods. Vinyloxyboranes, formed by reaction of trialkyl-boranes with diazoketones or by radical addition to methyl vinyl ketone, react with alkyl-lithium reagents to give the corresponding lithium enolates, which undergo facile, site-specific alkylation this allows the formation of aa-disubstituted ketones from diazoketones and a/3-disubstituted ketones from methyl vinyl ketone (Scheme 80). 

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