Ab initio study of 1,3-dioxanes formation from formaldehyde dimer and alkenes

Some features of adding formaldehyde dimer to alkenes with formation of alkyl-substituted 1,3-dioxanes by the Prins reaction in the gas phase are studied at the MP2(fc)/6-31G(d,p) computational level. The structure of the transition states and key intermediates is revealed and thermochemical reaction parameters are determined. It is shown that 1,3-dioxanes are mostly formed from the π-complex obtained in the result of formaldehyde dimer interaction with alkenes without intermediate formation of a σ-complex. Here the transformation of π-cation can be considered as a pseudo synchronous process. The synchrony degree and activation energy are considerably determined by the presence of alkyl substituents at the double bond.