Science of Synthesis

Kaufmann, D. E.; Burmester, C., Science of Synthesis, (2005) 6, 915.

The most versatile synthetic approach to propargylboranes uses the rearrangement of “ate” complexes. Both the reaction of alkynylboronates with halomethyllithium[‌4‌] as well as the homologation of halomethylboronates[‌9‌] have been used (‌Scheme 4‌). Although this is a relatively simple method for the preparation of isomerically pure propargylboronates, it has not been widely used so far. The boranes, prepared by this method, have not been isolated, but oxidized directly to propargyl alcohols with yields ranging from good to excellent (see Section ‌6.1.33.4‌). Recently, the scope of the homologation reaction has been extended to chiral propargylboranes.[‌12‌] The rearrangement of dialkynyl-/alkenyl-/hexylborates to propargylboranes has also been applied.[‌3‌] The reaction proceeds by migration of the alkenyl to one alkynyl group under intermediate formation of an allenylborane, which upon warming to room temperature isomerizes to a propargylborane.

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References