Preparations and Applications of Hexyleneglycol Organoboronic Esters
The preparation and reactivity of hexylene-glycol boronic esters (2-alkyl-, 2-vinyl- or 2-aryl-4,4,6-trimethyl-1,3,2-dioxaborinanes) are reviewed, with particular consideration for comparison with other stable boronic esters derived from pinacol or neopentylglycol. Hexylene-glycol boronic esters are efficiently prepared by various methods (quenching of organometallics with trialkoxyboranes, hydroborations, metal-catalyzed C–X and C–H borylations), starting from storable, readily available reagents. The hexylene-glycol boronic esters are air, water, and chromatography stable, and readily soluble in organic solvents. They can be superior in reactivity to pinacol boronic esters. The chapter aims to demonstrate that expensive, sometimes sluggishly reacting pinacol boronic esters should often be replaced by other, less expensive, more reactive boronic esters such as their hexylene-glycol counterparts in the context of modern metal-catalyzed reactions.