Functionalized carbocycles by tandem dealkoxycarbonylation-Michael addition reactions
摘要:
A tandem dealkoxycarbonylation-Michael addition reaction has been developed as a synthetic route to highly functionalized carbocycles. Methyl esters, activated toward decarboxylation by an electron-withdrawing group at C-2 and tethered by a three- or four-carbon chain to an acrylate Michael acceptor, have been prepared and used as the cyclization substrates. Treatment of these compounds with LiCl in HMPA at 120-degrees-C or 4 h results in selective S(N)2 dealkylation of the methyl esters, decarboxylation, and cyclization of the intermediate anions by a Michael addition to the pendant acrylate moiety. This affords 45-90% of the cyclopentane- and cyclohexaneacetic esters substituted at C-2 by an electron-with drawing group. Moderate to excellent selectivity (3:1-99:1) in favor of the product having the electron-withdrawing group trans to the acetic ester side chain is observed. The reaction works best for the preparation of five-membered rings, and cyclizations proceed most cleanly from substrates which cyclize through a tertiary carbanion. Synthetic and mechanistic details as well as optimization studies and product structure proofs are presented.
Functionalized carbocycles by tandem dealkoxycarbonylation-Michael addition reactions
摘要:
A tandem dealkoxycarbonylation-Michael addition reaction has been developed as a synthetic route to highly functionalized carbocycles. Methyl esters, activated toward decarboxylation by an electron-withdrawing group at C-2 and tethered by a three- or four-carbon chain to an acrylate Michael acceptor, have been prepared and used as the cyclization substrates. Treatment of these compounds with LiCl in HMPA at 120-degrees-C or 4 h results in selective S(N)2 dealkylation of the methyl esters, decarboxylation, and cyclization of the intermediate anions by a Michael addition to the pendant acrylate moiety. This affords 45-90% of the cyclopentane- and cyclohexaneacetic esters substituted at C-2 by an electron-with drawing group. Moderate to excellent selectivity (3:1-99:1) in favor of the product having the electron-withdrawing group trans to the acetic ester side chain is observed. The reaction works best for the preparation of five-membered rings, and cyclizations proceed most cleanly from substrates which cyclize through a tertiary carbanion. Synthetic and mechanistic details as well as optimization studies and product structure proofs are presented.
Carbocycles are essential building blocks for the synthesis of natural and synthetic bioactive compounds. Herein, we report the first example of palladium-catalyzed intramolecular carboalkynylation of non-activated olefins. Using activated carbonyl compounds as nucleophiles and an alkynyl bromide as an electrophile, the reaction gives access to cyclopentanes in 44-93% yield and one example of cyclohexane in 31% yield with simultaneous formation of a SP3-SP C-C bond. The reaction therefore combines ring formation with the introduction of a versatile triple bond for further functionalization. (C) 2015 Elsevier Ltd. All rights reserved.
Functionalized carbocycles by tandem dealkoxycarbonylation-Michael addition reactions
作者:Richard A. Bunce、Eric D. Dowdy、Paul B. Jones、Elizabeth M. Holt
DOI:10.1021/jo00077a043
日期:1993.12
A tandem dealkoxycarbonylation-Michael addition reaction has been developed as a synthetic route to highly functionalized carbocycles. Methyl esters, activated toward decarboxylation by an electron-withdrawing group at C-2 and tethered by a three- or four-carbon chain to an acrylate Michael acceptor, have been prepared and used as the cyclization substrates. Treatment of these compounds with LiCl in HMPA at 120-degrees-C or 4 h results in selective S(N)2 dealkylation of the methyl esters, decarboxylation, and cyclization of the intermediate anions by a Michael addition to the pendant acrylate moiety. This affords 45-90% of the cyclopentane- and cyclohexaneacetic esters substituted at C-2 by an electron-with drawing group. Moderate to excellent selectivity (3:1-99:1) in favor of the product having the electron-withdrawing group trans to the acetic ester side chain is observed. The reaction works best for the preparation of five-membered rings, and cyclizations proceed most cleanly from substrates which cyclize through a tertiary carbanion. Synthetic and mechanistic details as well as optimization studies and product structure proofs are presented.