Pd/Cu/TsOH-cocatalysed direct synthesis of 1,3-dienyl-2-boronic acid: a new reagent for homoallenylboration

Abstract

The homoallenylboration of carbonyls and imines using 1,3-dienyl-2-boron reagents is an appealing strategy for accessing synthetically valuable homoallenyl alcohols and amines. Nevertheless, existing reactive 1,3-dienyl-2-boron reagents generally suffer from drawbacks such as insufficient stability, limited structural diversity, or laborious synthesis and handling, which have significantly impeded the application of this transformation in synthetic chemistry. In this study, we present a novel class of 1,3-dienyl-2-boronic acids that are specifically designed for homoallenylboration. These reagents show sufficient stability and can be efficiently synthesized from structurally diverse and readily available 2,3-allenols via a ternary cocatalytic system involving palladium, copper, and TsOH. Moreover, preliminary investigations demonstrate that these 1,3-dienyl-2-boronic acids exhibit high reactivity towards both carbonyls and imines in the homoallenylboration reaction without the need for any additional catalyst, thereby establishing them as promising reagents for such transformations.