Intramolecular asymmetric C–H insertion of N-arylalkyl, N-bis(trimethylsilyl)methyldiazoamides mediated by chiral rhodium(II) catalysts. Synthesis of (R)-β-benzyl-γ-aminobutyric acid
摘要:
The enantio- and site-selectivity of the intramolecular C-H insertion reactions of acyclic N-arylalkyl, N-bis(trimethylsilyl)methyl alpha-diazoacetamides, and alpha-carboalkoxy-alpha-diazoacetamides 1a-g, catalyzed by chiral Rh(II) carboxamidates and Rh(II) carboxylates were studied. In general, the reaction showed good to excellent chemoselectivity. Regio selectivity for most of the reactions was high, but was also found to be influenced by the structure of the diazo substrate and the chiral Rh(II) catalyst employed. The highest enantioselectivity for the reactions catalyzed by chiral Rh(II) carboxamidates was 69% and Rh-2(4R-MEOX)(4) was found to be the most effective. For the chiral Rh(II) carboxylate catalyzed reactions, the highest ee obtained was 75% and Rh-2(S-PTTL)(4) is the optimal catalyst. The method was applied toward the synthesis of a GABA analogue, (R)-beta-benzyl-gamma-aminobutyric acid. (c) 2006 Elsevier Ltd. All rights reserved.
Asymmetric Intramolecular CH Insertion of α-Diazoacetamides in Water by Dirhodium(II) Catalysts Derived from Natural Amino Acids
作者:Nuno R. Candeias、Carolina Carias、Luis F. R. Gomes、Vânia André、M. Teresa Duarte、Pedro M. P. Gois、Carlos A. M. Afonso
DOI:10.1002/adsc.201200101
日期:2012.11.12
The asymmetricdirhodium(II)-catalyzed intramolecular CH insertion of α-diazo acetamides in water is described for the first time. The use of natural α-amino acids as chiral ligands allowed the preparation of novel dirhodium(II) homochiral complexes by a simple procedure consisting of the in situ ligand exchange starting from dirhodium tetraacetate. The catalytic system was further reused up to 7 cycles
The axial coordination of N-heterocycliccarbene ligands onto dirhodium(II) complexes was examined, together with its role in the intramolecular C-H insertion reactions of α-diazoacetamides. The formation of a decarbonylated product occurs by a free-carbene mechanism in which the structures of the catalyst and the acetamide play a decisive role. carbenoids - carbenecomplexes - catalysis - diazo compounds
The rhodium(II)-catalyzed reaction of N-bis(trimethylsilylmethyl)diazoamides: steric, electronic and conformational effects
作者:Andrew G.H Wee、Sammy C Duncan
DOI:10.1016/s0040-4039(02)01273-x
日期:2002.8
insertion reaction occurs only at the other N-‘alkyl’ unit. In Cα-unbranched diazoamides, the inherent electroniceffects of the N-‘alkyl’ group influence the regioselectivity of the reaction. The N-BTMSM group also influences the conformational preference about the amide N–Cα bond in Cα-branched systems which, in turn, affects the regioselectivity of the reaction; substituent electroniceffects are subtle