Lithium trialkylalkynylborates

The reaction of lithium trialkylalkynylborate and oxiranes has been described.A small amount of air initiates the 1,5-addition of the organo-borane and the oxirane by a radical mechanism to produce allenic derivatives (Eq. 

A different technique for the stannylation of an alkyne is shown in Scheme 8-1. Electrophiles add to the triple bond of lithium trialkylalkynylborates with migration of one of the alkyl groups to give a vinyl derivative, and when the electrophile is a trial-kyltin halide, the migrating group and the tin are situated trans.61 The ds-bimetallic alkene can then be demetallated providing a route to Z-alkenes, ketones, and alkynes. 9-BBN Can be used as the source of the boron to conserve a valuable alkyl group.62... 

Synthesis of t-alcohols. Lithium trialkylalkynylborates, when treated in THF with excess hydrochloric acid at room temperature or at reflux, undergo a double migration of alkyl groups from boron to carbon. Complexes containing... 

Reaction with lithium trialkylalkynylborates. Alkylation of borates (1), prepared as shown, with this bromide proceeds with migration of one alkyl group to give an intermediate (a), which is not isolated, but is oxidized to a... 

Lithium trialkylalkynylborates react stereoselectively with benzo-1,3-dithiolium fluoroborate to give functionalized vinylboranes (72) of mainly E-configuration (Scheme 37). Hydrolysis furnishes stereochemically pure E-a,/3-unsaturated aldehydes because the small proportion of Z-vinylborane is relatively stable. ... 

A. Pelter and L. Hughes. Michael reactions of lithium trialkylalkynylborates. J.C.S. Chem. Comm., 1977, 193. 

Trialkylalkynylborates with substituents in the alkyl chain of the alkyne unit may sometimes behave differently from the unsubstituted analogues. Thus, reaction of lithium 3-acetoxyalk-l-ynes with trialkylboranes gives allenyldialkylboranes which may be converted into allenes or alkynes (Scheme 14), ° whilst lithium 4-tosy-... 

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