Well‐Defined, Versatile and Recyclable Half‐Sandwich Nickelacarborane Catalyst for Selective Carbene‐Transfer Reactions

Abstract

Catalyticc arbene-transfer reactions constitute a class of highly useful transformations in organic synthesis. Although catalysts based on ar ange of transition-metals have been reported, the readily accessible nickel(II)-based complexes have been rarely used. Herein, an air-stable nickel(II)-carborane complex is reported as aw ell-defined, versatile and recyclable catalyst for selectivec arbene transfer reactions with low catalyst loading under mild conditions. This catalysti se ffective for several types of reactions including diastereoselectivec yclopropanation, epoxidation, selective XÀHi nsertions (X = C, N, O, S, Si), particularly for the unprotected substrates. This represents ar are example of carborane ligands in base metal catalysis.

Nickel‐Catalyzed Enantioconvergent Carboxylation Enabled by a Chiral 2,2′‐Bipyridine Ligand

“…Besides synthesis of pharmaceuticals directly, the chiral carboxylic acids could also serve as versatile synthetic intermediates (Scheme 3). For example, a nickelacarborane‐catalyzed O−H insertion with ethyl diazoacetate, using ( S )‐naproxen ( 2 ab ) as the reactant, smoothly produced ester 3 in 80 % yield, following our recently reported procedure [16] . Next, using a two‐step method, [17] the anti‐inflammatory drug naproxcinod 4 could be synthesized from 2 ab in 72 % yield.…”

“…Chemie medium gave slightly lower er value in comparison with the ternary system and for the latter two solvents, the yield was also significantly lower (entries [14][15][16].…”

“…Chemie in 80 % yield, following our recently reported procedure. [16] Next, using a two-step method, [17] the anti-inflammatory drug naproxcinod 4 could be synthesized from 2 ab in 72 % yield. Inspired by Yu's pioneering work using carboxylic acids as directing groups in CÀ H activation, [18] a Pdcatalyzed ortho arylation reaction of 2 ab with potassium phenyl trifluoroborates was tried and successfully afforded the acid 5 in 83 % yield.…”

Nickel‐Catalyzed Enantioconvergent Carboxylation Enabled by a Chiral 2,2′‐Bipyridine Ligand

“…In general, polar solvents such as N,N-dimethyl formamide (DMF), 2-methyltetrahydrofuran (2-MeTHF) or methanol (MeOH) were effective. Nonetheless, mono-component medium gave slightly lower er value in comparison with the ternary system and for the latter two solvents, the yield was also significantly lower (entries [14][15][16].…”

“…in 80 % yield, following our recently reported procedure. [16] Next, using a two-step method, [17] the anti-inflammatory drug naproxcinod 4 could be synthesized from 2 ab in 72 % yield. Inspired by Yu's pioneering work using carboxylic acids as directing groups in CÀ H activation, [18] a Pdcatalyzed ortho arylation reaction of 2 ab with potassium phenyl trifluoroborates was tried and successfully afforded the acid 5 in 83 % yield.…”