Stereoselective Control in the Alkylation and Annelation of Anions and Dianions Derived from 5-Norbornene-2,3-dicarboximides

Article abstract of DOI:10.1021/jo00340a014

Lithiation of endo- (1) or exo-4-phenyl-4-azatricyclo<5.2.1.0^2,6>hex-8-ene (2) with 2 equiv of lithium diisopropylamide gives a common dilithiated species which methylates predominantly from the side of the one-carbon bridge.Lithiation of 1 and 2 with 1 equiv of i-Pr2NLi gives different monolithiated species which methylate on opposite faces to give the products in which the cis stereochemistry of the ring function is retained.Sequential annelation of 1 and 2 with α,ω-dihalides involving formation of the monoanion, alkylation, formation of the alkylated monoanion, and intramolecular alkylation gives products in which the original stereochemistry of the product is retained.However, in the case of 2, the isomer with opposite stereochemistry is also obtained, presumably because of the formation of the dianion. endo-10,10-Diethoxy-4-phenyl-4-azatricyclo<5.2.1.0^2,6>hex-8-ene (14) gives a dilithiated species which methylates predominantly from the two-carbon bridge face, presumably because of the steric protection afforded by the ethoxy groups.Annelation of this species with 1,3-dibromopropane gives the product derived from reaction on the two-carbon bridge face and annelation with 1,4-dichlorobut-2-ene also gives predominantly the product resulting from attack on that side.