Comparative study of anionic and radical Cyclization for the preparation of 1,3-dimethylindans:: Highly stereoselective preparation of cis-1,3-disubstituted Indans via intramolecular carbolithiation

[GRAPHICS] The preparation of 1,3-dimethylindans from 4-(2-bromophenyl)-1-pentene (1) and 2-(2-lodo-1-methylethyl)styrene (2) substrates via radical-mediated cyclization and intramolecular carbolithiation has been investigated. Although cyclization of the radical derived from either substrate proceeds with modest selectivity for the cis-isomer, as does cycloisomerization of the aryllithium derived from substrate 1 (cis/trans;approximate to 2), intramolecular cyclization of the alkyllithium derived from substrate 2 is a highly cis-selective process (cis/trans = 12).