Allylic substitution reactions with Grignard reagents catalyzed by imidazolium and 4,5-dihydroimidazolium carbene–CuCl complexes

Abstract

Imidazolium and 4,5-dihydroimidazolium carbene-CuCl complexes effectively catalyzed the substitution reaction of allylic compounds with Grignard reagents in an S N 2 0 -selective fashion. It was noteworthy that the amount of the imidazolium carbene-CuCl complex could be reduced to 0.001 mol% and the catalysis recorded a high TON (10 5 ). Based on the experimental results, the atetype complex(es) such as [(imidazolium carbene)-CuR 2 ] À (MgX) + was postulated as an active species.

Copper‐Free Asymmetric Allylic Alkylation with Grignard Reagents

“…[1] The use of ligands that are based on an N-heterocyclic carbene (NHC) framework, first used in the asymmetric copper-catalyzed conjugate addition reaction, [2] was more recently introduced for the asymmetric allylic alkylation (AAA) reaction with great success. The groups of Okamoto, [3] Hong, [4] and Tomioka [5] used Grignard reagents as their organometallic reagent, whereas Hoveyda and coworkers [6] reported the use of diorganozinc and triorganoaluminum reagents. Most NHC ligands that have been reported thus far are C 2 symmetric; the Hoveyda group has developed a series of bidentate ligands wherein a free hydroxy group forms an intermediate alkoxy copper species (Figure 1).…”

Boryl Anion Attacks Transition‐Metal Chlorides To Form Boryl Complexes: Syntheses, Spectroscopic, and Structural Studies on Group 11 Borylmetal Complexes

“…From the chemical shifts, the following three features were found (Table 1): 1) all boryl complexes 4 a , b – 7 a , b showed characteristic downfield 11 B signals in the range of 38–50 ppm as observed for common dialkoxyboryl or diaminoboryl transition‐metal complexes;1 2) in the 13 C NMR spectra of 4 a , b – 6 a , b , resonances for the carbene carbon atom were shifted downfield compared to those of reference compounds 9 – 11 21. 23, 24 Notably, 13 C chemical shifts of the carbene carbon atom in borylgold(I) carbene complexes 6 a , b were close to those of the free carbene IMes ( 8 );23 and 3) the differences in the 13 C or 31 P chemical shifts between unsaturated system a and saturated system b are generally small.…”

Copper‐Catalyzed Silacarboxylation of Internal Alkynes by Employing Carbon Dioxide and Silylboranes

“…On the other hand, PBu 3 , PPh 3 , Xantphos, rac‐ BINAP, and DPPBz were not effective ligands, affording 2 a and 2 a′ in low yields (Table 1, entries 3–7). [CuCl(IMes)]12a bearing IMes, an N‐heterocyclic carbene (NHC) ligand, gave 2 in high yield, but with slightly lower regioselectivity ( 2 a / 2 a′ =88:12; Table 1, entry 8). [CuCl(IPr)],12b bearing the sterically demanding IPr ligand, gave a considerably lower yield (Table 1, entry 9).…”