The cycloaddition of substituted arynes to ketene dialkyl acetals to give benzocyclobutenone dialkyl ketals has been studied. Fifteen new derivatives of benzocyclobutene have been described. Theoretical structures of 18 substituted arynes have been calculated at the Becke3LYP/6-311G(d,p) level. The LUMO energies of 3- or 4-substituted arynes have been nicely correlated with the Hammett σm values. In order to determine the relative stability of the benzynes, the energies of aryne formation from corresponding subtituted benzenes (via 1,2-didehydrogenation reactions) have been calculated. The mechanism of the addition of benzyne to ketene dialkyl acetal has been discussed and a biradical pathway may account for the regioselectivity of the reaction. [Copyright &y& Elsevier]