Synthesis of some substituted 5,6,11,12-tetrahydro-dibenzo[a,e]cyclooctene derivatives through the intermediacy of tricarbonyl(η6-arene)chromium complexes

5,6,11,12-Tetrahydrodibenzo[a,e]cyclooctene derivatives with α- and β-substituents are readily accessible from [Cr(CO)3(5,6,11,12-tetrahydrodibenzo[a,e]cyclooctene)] 2 via a two-step sequence, which involves addition of a nucleophile and oxidation of the intermediate anionic cyclohexadienyl complex. Nucleophiles used included LiCMe2CN (A), LiCH2CN (B), and (C). The results show that the primary carbanion LiCH2CN and the S-stabilized carbanion give mixtures of α- and β-substituted products and in both cases α-isomers were major, whereas the opposite regioselectivity was obtained with the tertiary carbanion LiCMe2CN.