Copper-Catalyzed Asymmetric Borylative Ring Opening of Diazabicycles

Abstract

Highly enantioselective, copper-catalyzed ring opening of bicyclic hydrazines using a diboron reagent was accomplished with (R,R)-taniaphos as a chiral ligand. Desymmetrization of various bicyclic hydrazines by boryl substitution afforded 3-Bpin-4-hydrazino-cyclopentene derivatives with enantioselectivity up to >99% under mild conditions. The resulting allylic boron products were utilized in further organic transformations. Kinetic resolution of a racemic bicyclic oxazine gave useful information about the relative rates of C–O and C–N bond cleavage.

Copper-Catalyzed Borylative Difunctionalization of π-Systems

“…Tangential advancements that do not perform difunctionalizations include the asymmetric stereoconvergent borylation of alkyl halides, enantioselective borylcupration of ketones, aldehydes, and imines as well as asymmetric S N 2′ borylations − that were not covered in this review should all be considered in future developments and synthetic applications. The use of geminal diboronates in asymmetric copper catalysis has recently emerged for their addition to aldehydes, ketones, allyl systems, imines, , and Michael acceptors .…”

Activation of the Si–B interelement bond related to catalysis

“…A single example of a copper-catalysed silylative ring opening of diazabicycles was reported by Yun and co-workers (348 -349, Scheme 114). 135 The transformation occurred by C-N bond cleavage enabled by a copper/base/MeOH catalyst system, where MeOH fulfils the role of the proton source. By analogy, recently our group reported one example of a silylative ring-opening reaction of an aziridine (350 -351, Scheme 115).…”

Kinetic resolution of racemic 2-substituted 1,2-dihydroquinolines via asymmetric Cu-catalyzed borylation

“…On the other hand, chiral organoboron compounds, because of their utility in C–C and C–heteroatom bond formation, have greatly expanded the potential applications in organic chemistry, specifically as key intermediates in asymmetric synthesis. The direct catalytic enantioselective synthesis of organoboron compounds can be achieved by a number of reported methods, 12 such as hydroboration, 13 diboration, 14 arylborylation, 15 conjugate boron addition, 16 and allylic substitution. 17 Among these approaches, transition metal-catalyzed boration of prochiral C–C multiple bonds has recently attracted much interest in chemistry.…”