Addition of Carbon Nucleophiles to Tricarbonylchromium Complexes of 1,2‐Dihydrocyclobutabenzene, Indane, 1,2,3,4‐Tetrahydronaphtbalene and <i>ortho</i>‐Xylene

Abstract

Abstract 3‐Substituted 1,2‐dihydrocyclobutabenzenes (bicyclo[4. 2. 0]octa‐1,3,5‐triene) are readily accessible from [Cr(CO) 3 (1,2‐dihydrocyclobutabenzene)] ( 1 ) via a two‐step sequence which involves addition of a nucleophile and oxidation of the intermediate anionic cyclohexadienyl complex. Nucleophiles used include LiCMe 2 CN (A), LiCH 2 CN (B), LiC(Me)(OR)CN (C), (D), (E), LiCMe 2 CO 2 Me (F), and LiCH 2 CO 2 (t‐Bu) (G). [Cr(CO) 3 (Indane)] ( 2 ) also reacts highly regioselectively to give α‐substitution, whereas [Cr(CO) 3 (tetrahydronaphthalene)] ( 3 ) and [Cr(CO) 3 ( o ‐xylene)] ( 4 ) give mixtures of products. In several cases, the mixtures of the intermediate anionic cyclohexadienyl complexes can be equilibrated to give, after oxidation, β‐substituted derivatives of 1,2,3,4‐tetrahydronaphthalene and ortho ‐xylene selectively. EHMO calculations were carried out, and they rationalize the observed α‐regioselectivity of nucleophilic addition under kinetic control, The X‐ray structures of 1 and 4 are reported and in both compounds the Cr(CO) 3 group adopts in the solid state a staggered syn ‐conformation with respect to the substituted aromatic C‐atonis.