Alkoxide-Promoted Selective Hydroboration of N-Heteroarenes: Pivotal Roles of in situ Generated BH 3 in the Dearomatization Process

Abstract

© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim While numerous organo(metallic)catalyst systems were documented for dearomative hydroboration of N-aromatics, alkoxide base catalysts have not been disclosed thus far. Described herein is the first example of alkoxide-catalyzed hydroboration of N-heteroaromatics including pyridines, providing a broad range of reduced N-heterocycles with high efficiency and selectivity. Mechanistic studies revealed an unprecedented counterintuitive dearomatization pathway, in which 1) pyridine-BH 3 adducts undergo a hydride attack by alkoxyborohydrides, 2) in situ generated BH 3 serves as a catalytic promoter, and 3) 1,4-dihydropyridyl borohydride is in a predominant resting state ⓒ 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinh