Brønsted Acid Mediated Novel Rearrangements of Diarylvinylidenecyclopropanes and Mechanistic Investigations Based on DFT Calculations

Diarylvinylidenecyclopropanes undergo a novel rearrangement in the presence of the Brønsted acid Tf(2)NH (Tf: trifluoromethanesulfonyl) to give the corresponding naphthalene derivatives in good to high yields upon heating, whereas in the presence of the Brønsted acid toluene-4-sulfonic acid (p-TSA), the corresponding triene derivatives are afforded in moderate to good yields under mild conditions. Corresponding mechanistic studies on the basis of density functional theory (DFT) with the Gaussian03 program by using the B3LYP method have revealed that the pK(a) value of the Brønsted acid, as well as the entropy and solvent effects, plays a significant role in this reaction; these factors can discriminate the differences in the reactivity and regioselectivity among the Brønsted acids used in this reaction. In the presence of Lewis acid Sn(OTf)(2), a butatrienecyclopane can produce the corresponding ring-opened products in moderate yields.