Hydroalumination rearrangement

Mechanistically, the reaction proceeds through an alkynyl chloro alkoxide which, when treated with the reducing agent, is hydroaluminated to yield the vinyl alanate, which subsequently undergoes a facile pinacol-like 1,2-rearrangement. Excess hydride reagent reduces the intermediate alkenyl ketone and the resulting 2-alkenyl carbinol 1s isolated upon aqueous workup (Scheme). Table I contains representative examples. 

The most common version of this approach is the catalyzed reaction between the trimethylsilylmethyl Grignard reagent and various substrates, such as esters, enol derivatives, or vinyl halides (Scheme 71) i2°-i23 The same approach can be used to prepare enantiomerically pure allylsilanes using an appropriate catalyst (Scheme 72).124 Trimethylsilylmethyl cuprate reagents react with alkynes by syn carbocu-pration and the products can be treated further with electrophiles (Scheme 73).125 A quite different approach starting with an alkyne is to use a rearrangement set off by hydroalumination (Scheme 74).126... 

MacKay BA, Patrick BO, Fryzuk MD. Hydroalumination of a dinuclear tantalum dinitrogen complex N-N bond cleavage and ancillary Ugand rearrangement. Organometallics. 2005 24 3836-3841. 

Various reactions via hydrozirconation have been reported. The alkylzirconium intermediates are inexpensive and easy to prepare, requiring only moderate care in their handling, and undergoing a wide range of transformations under mild conditions with high yield. Hydrozirconation may prove an attractive alternate to hydroboration or hydroalumination processes, particularly when facile rearrangement of the functionalization unit is required... 

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