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

Abstract

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.

Broad Scope Extra‐Annular [4 + 2] Cycloaddition of o‐Carboryne with Styrenes: Efficient Route to Carborane‐Fused Polycyclics

“…of 1-OTf-o-1,2-C 2 B 10 H 11 (1) [6] using 1.05 equiv. of styrene 2a with o-carboryne generated in situ from 1 equiv.…”

“…13 C{ 1 H} NMR spectra were recorded on a Bruker DPX 400 spectrometer at 100 MHz or a Bruker DPX 500 spectrometer at 126 MHz. [6] All organic solvents were freshly distilled from Na/benzophenone or CaH 2 immediately prior to use. All signals were reported in ppm with reference to the residual solvent resonances of the deuterated solvents for proton and carbon chemical shifts, to external BF 3 ·OEt 2 (0.00 ppm) for boron chemical shifts.…”

“…[4,5] In general, o-carboryne can be generated in situ from 1-Br-2-Li-1,2-o-C 2 B 10 H 10 , 1-I-2-Li-1,2-o-C 2 B 10 H 10 , 1-Me 3 Si-2-[IPh(OAc)]-1,2o-C 2 B 10 H 10 , or 1-OTf-2-Li-1,2-o-C 2 B 10 H 10 . [5][6][7][8] It reacts with a broad spectrum of substrates including alkenes, alkynes, (hetero)aromatics, ethers, amines, and ferrocenes in various types of reaction manners such as [4 + 2]/[3 + 2]/[2 + 2] cycloaddition, [4a,4c-4h,7-13] ene reaction/hydrogen abstraction, [4b,4i] and sp 2 /sp 3 C-H bond insertion reaction [13,14] to give a large series of o-carborane derivatives that have received growing interests. [15] Scheme 1 Reaction of o-carboryne with styrenes As a highly reactive dienophile, o-carboryne is expected to undergo extra-annular [4 + 2] cycloaddition reaction with styrenes.…”

“…[9,10b] We spectulated that our newly developed o-carboryne precursor 1-OTf-2-Li-1,2-o-C 2 B 10 H 10 eliminating LiOTf at low temperatures may solve the chemoselectivity issue, [6][7][8] affording only extra-annular [4 + 2] cycloaddition products in the reaction with styrenes. [9,10b] We spectulated that our newly developed o-carboryne precursor 1-OTf-2-Li-1,2-o-C 2 B 10 H 10 eliminating LiOTf at low temperatures may solve the chemoselectivity issue, [6][7][8] affording only extra-annular [4 + 2] cycloaddition products in the reaction with styrenes.…”

Exceptionally Long C−C Single Bonds in Diamino‐o‐carborane as Induced by Negative Hyperconjugation

“…Recently,F okin, Schreiner, and co-workers reported the synthesis of hydrocarbons with extremely long CÀCbonds,stabilized by attractive London dispersion forces between two large diamondoid substituents [12][13][14] (Figure 1). [22] However,t here are relatively few known species with direct o-carboranyl C À N bonds [23][24][25][26][27][28][29] and no experimental report on the synthesis of 1,2-(NH 2 ) 2 -o-carborane. [15][16][17][18] Also for closo-1,2dicarbadodecaboranes,w ith formally hexa-coordinated carbon atoms and am ulticenter bonding situation, many experimental results reveal CÀCb onds that are longer than 174.8 pm.…”