Stereoselective synthesis of cis-1,3-disubstituted 1,3-dihydroisobenzofurans via arenechromium tricarbonyl methodology.

Article abstract of DOI:10.1016/0022-328X(89)80027-0

Phthalanchromium tricarbonyl is converted by t-butyllithium and alkyl halides completely stereoselectively into the corresponding exo-1-methyl, ethyl and benzyl derivatives.Double methylation of phthalanchromium tricarbonyl generates completely stereoselectively exo-cis-1,3-dimethylphthalanchromium tricarbonyl, from which cis-1,3-dimethylphthalan is liberated on oxidation.In contrast, double methylation of phthalan itself produces a 40/60 mixture of cis- and trans-1,3-dimethylphthalan.