A theoretical study on ketene-olefin cycloadditions. 1. Intermolecular reactions (original) (raw)

1990, The Journal of Organic Chemistry

The cycloaddition reaction between ketenes and olefins, leading to cyclobutanones, has been theoretidy studied by means of the semiempirical AM1 methodology. A representative set of 7 differently substituted ketenes and 3 olefins has been selected, and 50 transition states, corresponding to different ketene-olefin approach geometries, have been located and characterized. The reaction is seen to be concerted in all but in two cases, taking place through twisted transition states with small charge transfer from the olefin to the ketene. A reaction analysis by correlation of localized molecular orbitals shows that the reaction mechanism corresponds to the [,2, + (,2, + ,2J] description, rather to the [,2, + ,2,] one. The regioselectivity and the stereoselectivity of the reaction are correctly predicted by the calculations and are analyzed in terms of electronic and steric effects of the substituents on the reacting ketene and olefin partners. (2) (a) Markb, I.; Ronsmans, B.; Hesbain-Frisque, A. M.; Dumas, S.; Ghosez, L.; Ernst, B.; Greuter, H.