An Exogenous Base-Free Cu-Catalyzed Multicomponent Synthesis of 1,1-Aminoboranes from Alkylamines and Aldehydes

Abstract

An exogenous base-free, Cu-catalyzed multicomponent reaction for the synthesis of 1,1-aminoboranes from aldehydes, alkylamines, and bis(pinacolato)diboron (B2Pin2) is reported. This method provides direct access to isolable 1,1-amino(pinacol)boranes under operationally simple conditions with broad substrate scope, including secondary alkylamines that are inaccessible through conventional Cu-catalyzed borylations of electron-deficient imines. The resulting products can be isolated as either bench-stable hydrochloride salts or neutral 1,1-aminoboranes without chromatography. Additionally, they are readily prepared on gram-to-decagram scale and diversified through a range of downstream transformations. Preliminary mechanistic studies using kinetic experiments, catalyst structure–activity relationships, and reactivity probes reveal trends that differ substantially from those observed in imine borylation reactions conducted under conditions commonly associated with Cu−BPin formation. More broadly, these findings demonstrate how re-examining well-established reaction conditions can unlock next generation strategies for C−B bond formation while simultaneously expanding the synthetic utility of copper catalysis.