Construction of a Sterically Congested Carbon Framework via 5-Hexenyllithium Cyclization. Synthesis of (+/-)-Cuparene.

Article abstract of DOI:10.1016/S0040-4020(01)81931-1

The naturally occuring sesquiterpene (+/-)-cuparene <1,1,2-trimethyl-2-(4-methylphenyl)cyclopentane>, which contains two contiguous quaternary centers, is produced in good yield by 5-exo-trig cyclization of the 5-hexenyllithium (2) generated from 6-iodo-3,3-dimethyl-2-(4-methylphenyl)-1-hexene (3) by low temperature lithium-iodine exchange.In contrast, radical mediated cyclization of 3 proceeds via the 6-endo-trig mode to give 1,1-dimethyl-2-(4-methylphenyl)cyclohexane.