Intramolecular exocyclic alkene formation

The major interaction between these two molecules is between the nucleophilic end of the exocyclic alkene and the electrophilic end of the acrylate. These atoms have the largest coefficients in the HOMO and LUMO, respectively, and, in the transition state, bond formation between these two will be more advanced than anywhere else. For most ordinary alkenes and enophiles, Lewis acid catalysis to make the enophile more electrophilic, or an intramolecular reaction (or both ), is necessary for an efficient ene reaction. 

Covalent azides add to alkenes in a [2 + 3] cycloaddition, giving triazolines (Volume 4, Chapter 4.10), and these in turn can be thermolyzed or photolyzed with loss of nitrogen to give aziridines. The addition obeys the complementarity principle for cycloadditions, which in this case means that electron-rich azides prefer to react with electron-poor alkenes and vice versa. Thus, a few N-alkylaziiidines have been prepared from electron-poor alkenes via triazolines. The thermal stability of triazolines with respect to loss of nitrogen and aziridine formation varies with the electronegativity of the exocyclic N-sub-stituent. Thus, V-vinyltriazolines decompose more readily than N-alkyltriazolines to give V-vinylaziridines in good yield, as in Scheme 18. Several examples of intramolecular formation of... 

Intramolecular insertion into an exocyclic trisubstituted alkene was employed by Grigg and co-workers to construct a quaternary center in their total synthesis of the Amaryllidaceae alkaloid derivative (—)-crinane (44) [13]. Cyclization of aiyl iodide 41 using tri-o-tolylphosphine as ligand afforded a 20 1 mixture of trans and cis tricyclic products 42 and 43 in good yield. Predominant formation of the trans ring juncture observed in this example is unusual. 

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