Protonation pattern as a controlling factor of thermal reactions of aryl o-divinylbenzenes in acidic media: an integrated experimental–theoretical study†

The thermal transformations of various thienyl and phenyl derivatives of o-divinylbenzene in acidic media were investigated in an integrated experimental–theoretical study. Several derivatives (9–12) led to cyclization products when heated under acidic conditions, while some (13 and 14) were found to be non-reactive. The reactivity or non-reactivity of the investigated compounds is closely related to the position of the preferred protonation site in the investigated compounds, as shown by DFT calculations. If the preferred position of proton entry into the molecule coincides with the protonation position required for cyclization, the reaction proceeds, otherwise the derivatives are non-reactive. By blocking a preferred protonation position with a suitable substituent in the non-reactive precursors, protonation can be prevented at the undesired site and proton entry can be redirected to the site that allows the reaction to proceed. A detailed insight into the mechanism of the thermal reactions of 9–12 was presented.