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Royal Society of Chemistry, Dalton Transactions, 14(45), p. 6060-6070, 2016

DOI: 10.1039/c5dt03003j

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The carboboration of Me3Si-substituted alkynes and allenes with boranes and borocations

This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

The 1,1-carboboration of 1-Me3Si-1-alkynes is the dominant reaction observed using [PhBCl(2-DMAP)][AlCl4], , and PhBCl2 electrophiles, with highly substituted vinyl pinacol boronate esters isolated post esterification. Other aryl and heteroaryl congeners of both and PhBCl2 have a limited scope in the 1,1-carboboration of 1-Me3Si-1-alkynes, with desilylboration more prevalent. PhBCl2 converts Me3Si-substituted allenes to allylboranes via a formal 1,3-carboboration with Me3Si-migration. [Cl2B(2-DMAP)][AlCl4] reacts with a number of 1-Me3Si-1-alkynes by desilylboration, whilst with Me3Si-ethyne a 1,1-boroamination reaction proceeds, which with excess boron electrophile is followed by an intermolecular desilylboration to form a tricationic-borate. The use of excess 1-Me3Si-1-propyne relative to (and a thienyl congener of ) formed 2-boradienes in low yields from the reaction with two equivalents of alkyne. Vinyl borocations ligated by 2,6-lutidine of the general formula, [(vinyl)BCl(2,6-lutidine)][AlCl4] formed 1-boradienes with 1-Me3Si-1-alkynes.