Copper-Catalyzed Ring-Opening/Borylation of Cyclopropenes

Abstract

Because organoboron compounds readily undergo a diverse array of transformations and are widely used in various fields, the development of C-Bbond-forming reactions have attracted considerable attention. Herein we report a new method for forming C-B bonds by means of Cucatalyzed ring-opening/borylation reactions of cyclopropenes. This method provides efficient access to a new type of stable allylborane-Lewis base adduct, which is a versatile synthon. The configuration of the products can be well controlled with this method, and some of the configurations we obtained are inaccessible by means of other catalytic methods for generating allylborons. Mechanistic studies indicated that the reactions proceed via insertion of an alkenyl Cu carbene-generated in situ by cyclopropene ring opening-into the B-H bond; the ring-opening step determines both the rate and the stereochemistry.

Uncommon carbene insertion reactions

“…Transition-metal-catalysed ring-opening of cyclopropenes generates vinyl metal carbenes, which could be captured by borane adducts to produce allylboranes. Quit recently, Zhu et al 35 presented a Cu( i )-catalysed ring-opening/borylation reaction of cyclopropenes, delivering γ , γ -disubstituted allylboranes with moderate to good yields and regioselectivities ( Scheme 8a ). Interestingly, the regioselectivity arises from the steric bias between the two substituents installed at the 3,3-position of cyclopropenes in the ring-opening step, and for 3-alkyl-3-aryl cyclopropenes, the regioselectivity can be further regulated because the Z -carbene tends to undergo intramolecular C–H bond insertion, leaving the E -type products only ( Scheme 8b ).…”

A copper-catalyzed B–H bond insertion reaction of azide–ynamide with borane adductsviaα-imino copper carbenes

“…1 In the past decade, carbene insertion into the B–H bond of borane adducts catalyzed by transition metals has been developed as a remarkable method for the construction of the C–B bond (Scheme 1a). 2 In 2013, Curran's group reported a rhodium-catalyzed B–H bond insertion reaction of NHC–boranes with diazo compounds, and a range of α-NHC–boryl carbonyls were generated in good yields. 3 Simultaneously, Zhou and Zhu realized the first example of asymmetric B–H insertion reactions, affording a series of chiral α-boryl acetates in good yields with excellent enantioselectivities.…”

Stereoselective ZnCl2-Catalyzed B–H Bond Insertion of Vinyl Carbenes Generated from Cyclopropenes for the Synthesis of Allylboranes

“…Studies in this area focus, on the one hand, on the development of suitable carbene precursors and, on the other hand, on the exploration of efficient catalytic methods . With regard to the development of catalytic systems, transition-metal catalysts including rhodium­(II), , rhodium­(I), copper­(I), , gold­(I), iridium­(I), and ruthenium­(II) have been applied by the groups of Curran, Xu, Zhu, Wang, Zhang, and Iwasa (Scheme a). Despite the broad studies, currently, the use of nonprecious metals as catalysts in the insertion of carbenes into B–H bonds still remains very limited, leaving great space for the development of new catalytic methods that involve metals with high abundance and low price.…”