Sigmatropic shift reactions symmetry effects

Just as there are secondary interactions in cycloadditions, so too are there ancillary orbital-symmetry effects in sigmatropic reactions. In process (79), Jones and Jones (1967) find no products of [1,3] hydrogen or methyl shifts, e.g. 1,4,7-trimethylheptatriene, which ostensibly (Table 5) are photochemically allowed. They point out that in the first... 

Abstract The integration of conservation of orbital symmetry and the orbital overlap effect serves as a powerful tool to reliably predict the stereochemical course of pericyclic reactions as exemplified in this chapter. The orbital overlap factor has been discussed with a variety of examples such as the thermal fragmentations of cyclopropanated and cyclobutanated r .v-3,6-dimethyl-3,6-dihydropyridazine, and [1,5] sigmatropic shifts in c/.v-2-alkenyl-1 -alkylcyclopropanes and civ-2-alkenyl-1 -alkylcyclobutanes. 

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