Cyclization of Aryllithiums Tethered to Methylenecycloalkanes: Stereoselective Synthesis of 4a-Substituted cis-Hexahydrofluorenes
摘要:
The cyclization of an aryllithium tethered to a methylenecycloalkane, generated from 2-(o-bromobenzyl)-1-methylenecycloalkanes 1, 2, and 3 by low-temperature lithium-bromine exchange, has been found to be a kinetically slow but thermodynamically favorable process that proceeds at a convenient rate in an exclusively 5-exo fashion when solutions of the aryllithium in n-heptane-di-n-butyl ether (9:1 v/v) are warmed to 45 degreesC. The cyclization affords stereoisomerically pure cis-fused products (7 and 8) when the methylenecycloalkane is five- or six-membered but it is less stereoselective when the methylenecycloalkane is seven-membered. The ring-closure of the aryllithium derived from 2-(o-bromobenzyl)-1-methylenecyclohexane (2) provides an experimentally convenient route to stereoisomerically pure 4a-substituted cis-hexahydrofluorenes in 60-90% isolated yield.
Cyclization of Aryllithiums Tethered to Methylenecycloalkanes: Stereoselective Synthesis of 4a-Substituted cis-Hexahydrofluorenes
摘要:
The cyclization of an aryllithium tethered to a methylenecycloalkane, generated from 2-(o-bromobenzyl)-1-methylenecycloalkanes 1, 2, and 3 by low-temperature lithium-bromine exchange, has been found to be a kinetically slow but thermodynamically favorable process that proceeds at a convenient rate in an exclusively 5-exo fashion when solutions of the aryllithium in n-heptane-di-n-butyl ether (9:1 v/v) are warmed to 45 degreesC. The cyclization affords stereoisomerically pure cis-fused products (7 and 8) when the methylenecycloalkane is five- or six-membered but it is less stereoselective when the methylenecycloalkane is seven-membered. The ring-closure of the aryllithium derived from 2-(o-bromobenzyl)-1-methylenecyclohexane (2) provides an experimentally convenient route to stereoisomerically pure 4a-substituted cis-hexahydrofluorenes in 60-90% isolated yield.
A highly regioselective 6-endo-aryl radical cyclisation: stereocontrolled synthesis of trans-octahydroanthracenes
作者:Sitaram Pal、Monika Mukherjee、Debi Podder、Alok K. Mukherjee、Usha Ranjan Ghatak
DOI:10.1039/c39910001591
日期:——
The sterocontrolled synthesis of trans-octahydroanthracenes 3, 11 and 14 through implementation of an efficient and highly regioselective 6-endo-trig-aryl radical cyclisation of the respective 2-(o-bromobenzyl)-1-methylenecyclohexanes 2, 10 and 13, with tri-n-butyltin hydride is reported, along with a single crystal X-ray structure determination of 11.
Bu(3)SnH-mediated aryl radicalcyclizationonto methylenecycloalkanes having a phenylthio, an ester, or a nitrile group at the terminus of the alkenic bond provides exclusively exo cyclization products. The results are in sharp contrast to those reported for nonsubstituted methylenecycloalkanes, which give exclusively endo cyclization products. Formation of endo cyclization products has been suggested
An Efficient Palladium Catalyzed Stereocontrolled Synthesis of 4a-Angular Methyl Substituted Hydrofluorenes
作者:Jayanta K. Mukhopadhyaya、Sitaram Pal、Usha Ranjan Ghatak
DOI:10.1080/00397919508015849
日期:1995.6
A high yield s tereoselective synthesis of 4a-angularly methyl substituted cis-hexahydrofluorenes 5a-h and tetrahydrofluorenes 7a,b has been developed by palladium-catalyzed intramolecular Heck-type cyclization of the respective exo-olefins 4a-h and 4a,b through exclusive 5-exo-trig mode.
Regioselective Aryl Radical Cyclization. 1. Stereocontrolled Synthesis of Linearly Condensed Hydroaromatic Carbocyclic Systems through 6-endo-Ring Closures
作者:Sitaram Pal、Jayanta K. Mukhopadhyaya、Usha Ranjan Ghatak
DOI:10.1021/jo00089a009
日期:1994.5
The stereocontrolled synthesis of trans-octahydroanthracenes 3, 11a-c, and 14a-c and trans-octahydro-5aH-cyclohepta[b] naphthalene (27) through implementation of an efficient and highly regioselective 6-endo-trig-aryl radical cyclization of the respective 2-(o-bromoaryl)-1-methylenecyclohexanes 2, 10a-c, and 13a-c and 2-(o-bromobenzyl)-1-methylenecycloheptane (41) with tri-n- butyltin-hydride-is described. The radical cyclization of 2-(o-bromobenzyl)-1-methylenecyclopentane (43), in contrast, produced a mixture of the cis- and trans-hexahydro-1H-benz[f]indenes (38) and (37).