Carboranes are carbon–boron molecular clusters, which can be viewed as three-dimensional analogues to benzene. They are finding many applications in medicine, materials and organometallic chemistry. On the other hand, their exceptional thermal and chemical stabilities, as well as 3D structures, make them very difficult to be functionalized, in particular the regioselective functionalization of BH vertex among ten similar B–H bonds. Here we report a very efficient iridium-catalysed borylation of cage B(3,6)–H bonds of o-carboranes with excellent yields and regioselectivity using bis(pinacolato)diboron (B2pin2) as a reagent. Selective cage B(4)–H borylation has also been achieved by introducing a bulky TBDMS (tert-butyldimethylsilyl) group to one cage carbon vertex. The resultant 3,6-(Bpin)2-o-carboranes are useful synthons for the synthesis of a wide variety of B(3,6)-difunctionalized o-carboranes bearing cage B–X (X=O, N, C, I and Br) bonds.
The efficient o-carboryne precursor 1-Li-2-OTf-o-C2 B10 H10 reacts with lithium amides at room temperature to give a series of N-carboranyl amines in moderate to high isolated yields. This reaction is compatible with a broad substrate scope from primary to secondary, alkyl to aryl amines. The reaction mechanism is also proposed on the basis of experimental results and DFT calculations. This represents the first general and efficient method for the synthesis of 1-NR(1) R(2) -o-carboranes.
Carborane cage chirality is an outstanding issue of great interest as the icosahedral carboranes have wide applications in medicinal and materials chemistry. The synthesis of optically active carborane derivatives, whose chirality is associated with the substitution patterns on the polyhedron, will open new avenues to carborane chemistry. We report herein an efficient method to achieve chiral-at-cage arylation of o-carboranes with high regio- and enantioselectivities by a strategy of palladium-catalyzed asymmetric intramolecular B-H arylation and cyclization. This represents the first example of the enantioselective reaction on carboranes, providing an efficient way for the construction of chiral-at-cage compounds with new skeletons.
The asymmetric synthesis of chiral-at-cage o-carboranes, whose chirality is associated with the substitution patterns on the polyhedron, is of great interest as the icosahedral carboranes have wide applications in medicinal and materials chemistry. Herein we report an intermolecular Ir-catalyzed enantioselective B−H alkenylation for efficient and facile synthesis of chiral-at-cage o-carboranes with new skeletons under mild reaction conditions. Generally very good to excellent yields with up to 99% ee can be achieved in this Ir-catalyzed B−H alkenylation. The enantiocontrol model is proposed based on Density Functional Theory calculations in which the use of chiral phosphoramidite ligand is essential for such asymmetric o-carborane B−H alkenylation.
Iridium‐catalyzed formal alkyne hydroboration with cage B−H of o‐carborane has been achieved, leading to the controlled synthesis of a series of 3,6‐[trans‐(AlkCH=CH)]2‐o‐carboranes (Alk=alkyl), 3‐cis‐(ArCH=CH)‐o‐carboranes (Ar=aryl), and 3‐cis‐(ArCH=CH)‐6‐trans‐(AlkCH=CH)‐o‐carboranes in high yields with excellent regio‐ and very good cis–trans selectivity. The most electron‐deficient B(3,6)−H vertices favor oxidative addition on electron‐rich metal centers, which is responsible for the regioselectivity. On the other hand, the configuration of the resultant olefinic units is dominated by alkyne substituents. Alkyl groups lead to a trans‐configuration whereas bulky aryl substitutions result in cis‐configuration.
of main observation and conclusion A palladium catalyzed oxidative annulation of 1-hydroxy-o-carborane with internal alkynes via regioselective B(3)-H bond activation has been developed for facile synthesis of a series of C,B-substituted carborane-fused oxaboroles. These molecules can undergo intramolecular oxidative dehydrogenative coupling to afford carborane-fused large π systems for potential applications in organic materials. The reaction mechanism is also proposed, involving hydroxy deprotonation, nucleopalladation of alkyne, regioselective electrophilic B-H substitution and reductive elimination.
An efficient Ir-catalyzed cage boron vertex alkenylation of 1-(2’-picolyl)-o-carboranes with diarylacetylenes has been developed, leading to a wide variety of B–H geminal addition products via 1,2-carbon migration of alkynes. The...
N‐Carboranyl amines have potential applications in medicinal chemistry and catalysis. How to prepare them is a challenging task. In their Communication on page 1751 ff., Z. Qiu, Z. Xie et al. approach this challenge by developing a new carboryne precursor 1‐OTf‐o‐C2B10H11, which reacts very efficiently with lithium amides to give a wide range of new N‐carboranyl amines.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.