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 LiCMe2CN (A), LiCH2CN (B), LiC(Me)(OR)CN (C),[...], LiCMe2CO2Me (F), and LiCH2CO2(t-Bu) (G). [Cr(CO)3(Indane)] (2) also reacts highly regioselectively to give a-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, ß-substituted derivatives of 1,2,3,4-tetrahydronaphthalene and ortho-xylene selectively. EHMO calculations were carried out, and they rationalize the observed a-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.