10 Reaction mechanisms Part (iii) Pericyclic reactions

Abstract

Computational studies of pericyclic reaction mechanisms have greatly enhanced our understanding of, and predictions regarding, reaction mechanisms. In recent years, the importance of non-statistical effects in pericyclic reactions, as studied using dynamics trajectory calculations, has been recognized. Some examples are the electrocyclic ring opening of the cyclopropyl radical, the Cope rearrangement of hepta-1,2,6-triene, and the rearrangement of bicyclo[n.1.0]polyenes. High quality mechanistic studies, though becoming less common, were also carried out. For example, two studies were published on vinylcyclobutane derivatives, one focusing on the thermal stereomutations and cycloreversions, and the other on the [1,3] sigmatropic reactions. The strength of the interplay between experiment and theory is demonstrated in studies of the intramolecular [4+2] cycloaddition of cyclobutadiene with tethered alkenes, in the use of isotope effects to determine the mechanism of an electron-transfer catalyzed Diels–Alder reaction, and in the degenerate interconversions of bicyclo[3.1.0]hex-2-ene.