Stereochemistry of metal-halogen exchange-initiated intramolecular conjugate addition reactions in the construction of 5-membered carbocycles
摘要:
The stereochemistry of some lithium-iodine exchange-initiated cyclization reactions of model omega-iodo, gamma-substituted activated olefins has been studied. The stereoselectivities of these anionic cyclization reactions have been found to be a function of the olefin activator employed, reaction conditions, Michael acceptor olefin geometry, the nature of the gamma-substituent, and, in some cases, the presence of additives. Cyclization reactions of iodides possessing E olefin geometry give a moderate preference for trans cyclopentane formation while Z olefin geometry leads to extremely high (> 300:1) trans product selectivity. Cyclization reactions of E olefins under radical conditions were found to be slightly more trans-selective than those observed under anionic conditions although Z olefin geometry again promotes very high trans product selectivity. The presence of the allylic methoxyl group in (E)-7d leads to cis selectivity under both anionic and radical conditions. Intramolecular complexation involving the reactive carbon center and the methoxyl group is suggested in both modes as a possible explanation for this cis product selectivity.
Stereochemistry of metal-halogen exchange-initiated intramolecular conjugate addition reactions in the construction of 5-membered carbocycles
摘要:
The stereochemistry of some lithium-iodine exchange-initiated cyclization reactions of model omega-iodo, gamma-substituted activated olefins has been studied. The stereoselectivities of these anionic cyclization reactions have been found to be a function of the olefin activator employed, reaction conditions, Michael acceptor olefin geometry, the nature of the gamma-substituent, and, in some cases, the presence of additives. Cyclization reactions of iodides possessing E olefin geometry give a moderate preference for trans cyclopentane formation while Z olefin geometry leads to extremely high (> 300:1) trans product selectivity. Cyclization reactions of E olefins under radical conditions were found to be slightly more trans-selective than those observed under anionic conditions although Z olefin geometry again promotes very high trans product selectivity. The presence of the allylic methoxyl group in (E)-7d leads to cis selectivity under both anionic and radical conditions. Intramolecular complexation involving the reactive carbon center and the methoxyl group is suggested in both modes as a possible explanation for this cis product selectivity.
Stereochemistry of metal-halogen exchange-initiated intramolecular conjugate addition reactions in the construction of 5-membered carbocycles
作者:Manning P. Cooke
DOI:10.1021/jo00031a031
日期:1992.2
The stereochemistry of some lithium-iodine exchange-initiated cyclization reactions of model omega-iodo, gamma-substituted activated olefins has been studied. The stereoselectivities of these anionic cyclization reactions have been found to be a function of the olefin activator employed, reaction conditions, Michael acceptor olefin geometry, the nature of the gamma-substituent, and, in some cases, the presence of additives. Cyclization reactions of iodides possessing E olefin geometry give a moderate preference for trans cyclopentane formation while Z olefin geometry leads to extremely high (> 300:1) trans product selectivity. Cyclization reactions of E olefins under radical conditions were found to be slightly more trans-selective than those observed under anionic conditions although Z olefin geometry again promotes very high trans product selectivity. The presence of the allylic methoxyl group in (E)-7d leads to cis selectivity under both anionic and radical conditions. Intramolecular complexation involving the reactive carbon center and the methoxyl group is suggested in both modes as a possible explanation for this cis product selectivity.