Remarkable template effect of a Lewis acid receptor in the intramolecular radical cyclization: control of reaction pathway as well as stereochemistry

A remarkable template effect in the intramolecular radical cyclization process has been observed by the successful utilization of Lewis acid receptor, aluminum tris(2,6-diphenylphenoxide) (ATPH). The origin of this efficient template effect by ATPH would be ascribable to the well-defined reaction environment created in front of the aluminum coordination center; this enables appropriate proximity of initially generated carbon radical to unsaturated carbon–carbon bond in the transition state for smooth cyclization and hence completely suppresses the undesired intermolecular reduction pathway. Moreover, such conformational restriction provided by the unique cavity of ATPH alters the stereoselectivity of the cyclization.