WHY DO CATALYTIC QUANTITIES OF LEWIS-ACID GENERALLY YIELD MORE PRODUCT THAN 1.1-EQUIV IN THE INTRAMOLECULAR DIELS-ALDER REACTION WITH A FURAN DIENE - COMPETITIVE COMPLEXATION NMR-STUDIES PROVIDE AN ANSWER

The results presented here provide experimental support for a hypothes is made by us to rationalize literature observations on intramolecular Diels-Alder reactions (IMDA) and our own observations on IMDA with a furan diene (IMDAF) regarding the quantity (catalytic or stoichiometri c) of Lewis acid required to facilitate reaction. Evidence suggests th at the reactions can be divided into two classes::those that proceed w ith catalytic quantities of Lewis acid (herein defined as type A) and those that require a stoichiometric quantity of Lewis acid (type B). W e believe that the relative basicity of the controlling functional gro ups in addend and adduct can be critical in determining the quantity o f Lewis acid required. The relative Lewis basicity has been studied us ing competitive complexation studies using low-temperature NMR experim ents to study the coordination of methylaluminum dichloride (MAC)and B F3.Et(2)O with model oxygen Lewis bases and IMDAF addends and adducts.