Intramolecular Reactions Donor-Bridge-Acceptor Systems

Intramolecular Reactions Donor-Bridge-Acceptor Systems... 

Intramolecular reactions between donor and acceptor centres in fused ring systems provide a general route to bridged polycyclic systems. The cts-decalone mesylate given below contains two d -centres adjacent to the carbonyl function and one a -centre. Treatment of this compound with base leads to reversible enolate formation, and the C-3 carbanion substitutes the mesylate on C-7 (J. Gauthier, 1967 A. Belanger, 1968). 

There are several fundamental reasons why the GMH and adiabatic formulations are to be preferred over the traditionally employed diabatic formulation. The definition of the diabatic basis set is straightforward for intermolecular ET reactions when the donor and acceptor units are separated before the reaction and form a donor-acceptor complex in the course of diffusion in a liquid solvent. The diabatic states are then defined as those of separate donor and acceptor units. The current trend in experimental design of donor-acceptor systems, however, has focused more attention on intramolecular reactions where the donor and acceptor units are coupled in one molecule by a bridge.The direct donor-acceptor overlap and the mixing to bridge states both lead to electronic delocalization, with the result that the centers of electronic localization and localized diabatic states are ill-defined. It is then more appropriate to use either the GMH or adiabatic formulation. 

Depending on the positioning of the bridge linking the ene donor and acceptor, three orientations are possible for the intramolecular ene reaction. These have been described by Oppolzer (1) as Types I, II, and III. Snider (5) has observed, in addition. Type IV [3]. Type I reactions are by far the most studied, especially for five- and six-membered ring forming reactions. It is conceivable, especially as activated ene systems are developed, that Types II-IV will become more important. 

---