Facile Synthesis of N‐Carboranyl Amines through an ortho‐Carboryne Intermediate

Abstract

The efficient o-carboryne precursor 1-Li-2-OTf-o-C 2 B 10 H 10 reacts with lithium amides at room temperature to give as eries of N-carboranyl amines in moderate to high isolated yields.T his reaction is compatible with ab road substrate scope from primary to secondary,a lkyl to aryl amines.The reaction mechanism is also proposed on the basis of experimental results and DFT calculations.T his represents the first general and efficient method for the synthesis of 1-NR 1 R 2 -o-carboranes.Amine derivatives are ubiquitous in biology and very important functional units in medicinal chemistry,w hich can be generally synthesized by alkylation of ammonia or amines, reduction of nitriles,azides,orimines,and hydroamination of alkenes or alkynes. [1] On the other hand, ag rowing interest has been directed toward the synthesis of o-carborane derivatives bearing organic nitrogen groups owing to their potential applications in medicinal chemistry [2] and catalysis. [3] Fore xample,c arborane-amino acid or -nucleoside combinations serve as excellent candidates for cancer treatment in boron neutron capture therapy (BNCT). [2b-e,4] Moreover, aminoalkyl-o-carboranes have been extensively employed as ligands for transition metal complexes. [3,5] Despite the recent advances in carborane chemistry,t he straightforward and general synthesis of amino-o-carboranes,inparticular, 1-R 2 No-carboranes,s till represents av ery challenging project. [6] It has been documented that 1-NH 2 -o-C 2 B 10 H 11 can be prepared by reduction of azido-or nitroso-o-carborane or by Curtius rearrangement of the carboranyl amide. [7][8][9] However, unlike organic amines,1 -NH 2 -o-carborane does not undergo alkylation/arylation to give the corresponding 1-RNH-ocarborane or 1-R 2 N-o-carborane. [10] Unfortunately,t here are no other convenient methods to prepare these amines. [6,11] Very recently,wereported that o-carboryne, [12] generated in situ from 1-iodo-2-lithio-o-carborane,c an undergo a-CÀH bond insertion with tertiary amines,a ffording a-carborany-Scheme 1. Reaction of o-carboryne with amines.

Synthesis, Characterization, and Properties of Three-Dimensional Analogues of 9-Borafluorenes

“…The three-dimensional (3D) aromatic ortho -carboryne can be viewed as a 3D analogue of benzyne . In fact, the 2D/3D relationship sparked great interest in the synthesis and property studies of 3D analogues of boron-doped polycyclic π-conjugated hydrocarbons, being highlighted by the recent reports on the 3D analogues of benzoborirene, ,, 9,10-diboraanthracene (DBA), , and 9-borafluorene. , In general, thanks to the powerful electronic and kinetic stabilization effect , of o -carborane and the strong electron-withdrawing inductive effect at its C -positions, ,, the 3D analogues feature boosted Lewis acidity as well as enhanced stability with respect to the corresponding 2D π systems. The first 3D 9-borafluorenes were reported in 2019 by Martin and co-workers (Figure c), but with the B -substituent limited to amino groups .…”