Divergent Elementoboration: 1,3-Haloboration versus 1,1-Carboboration of Propargyl Esters

Lewis C Wilkins; Yashar Soltani; James R Lawson; Ben Slater; Rebecca L Melen

doi:10.1002/chem.201801493

Divergent Elementoboration: 1,3-Haloboration versus 1,1-Carboboration of Propargyl Esters

Chemistry. 2018 May 23;24(29):7364-7368. doi: 10.1002/chem.201801493. Epub 2018 Apr 27.

Authors

Lewis C Wilkins¹, Yashar Soltani¹, James R Lawson¹, Ben Slater², Rebecca L Melen¹

Affiliations

¹ School of Chemistry, Cardiff University, Main Building, Park Place, Cardiff, CF10 3AT, Cymru/Wales, UK.
² Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, UK.

Abstract

This work showcases the 1,3-haloboration reaction of alkynes in which boron and chlorine add to propargyl systems in a proposed sequential oxazoliumborate formation with subsequent ring-opening and chloride migration. In addition, the functionalization of these propargyl esters with dimethyl groups in the propargylic position leads to stark differences in reactivity whereby a formal 1,1-carboboration prevails to give the 2,2-dichloro-3,4-dihydrodioxaborinine products as an intramolecular chelate. Density functional theory calculations are used to rationalize the distinct carboboration and haloboration pathways. Significantly, this method represents a metal-free route to highly functionalized compounds in a single step to give structurally complex products.

Keywords: Lewis acid; alkynes; boranes; boron; haloboration.