Hydroalumination adducts

Thirdly, although proton-aluminum exchange may not occur with the starting R2AIH (equation 19), it may be significant between the hydroalumination adduct and the unconsumed terminal alkyne (equation 21). ... 

The second side reaction with alkenes is the configurational change at the jp -hybridized carbon-aluminum bond in the hydroalumination adduct (equation 31). ... 

Distinctly less is known about the anti hydroalumination adducts obtained from alkynes with MAIH4 or MAIR3H reagents (equation 9). These adducts could be the direct result of a trans addition but, pending further information, they might also arise from initial syn addition and subsequent isomerization. 

Once the hydroalumination adducts of C=C and C C bonds have been cleanly formed, protolysis or oxidation can produce useful derivatives. With H2O or O2, generally all available C—Al bonds are destroyed. Protolysis or deuteriolysis of such adducts constitutes an overall reduction or deuteriating reduction of the original C—C unsaturation (equations 13, 39 and 41 Schemes 6-8). ° Any stereoselectivity or regioselectivity of the original hydroalumination is preserved. 

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