Accelerated Electrocyclic Ring-Opening of Benzocyclobutenes under the Influence of a beta-Silicon Atom

摘要

Interconversion between cyclobutenes and 1,3-dienes is one of the most familiar and fundamental electrocyclic reactions.Thermal conrotatory process of this reaction has been proven by both theoretical and experimental studies,and the direction of the conrotation,either inward or outward in the case of 3-substituted cyclobutenes (i.e.,"torquoselectivity"),has been increasingly predictable owing to the extensive research in this field.In particular,recent topical reports on this subject have dealt with a remarkable effect of 3-silyl substituents,which prefer inward rotation despite the steric congestion and significantly accelerate the electrocyclic ring-opening reaction.Similar cleavage rate enhancement of cyclobutenes has also been documented for the 3-hydroxy (and its anion) and 3-dithioketal derivatives as well as the cyclobutenes bearing an adjoining carbanion stabilized by a sulfur or a phosphorus atom at the 3-position.It is expected that these substituent effects affecting the rate of the electrocyclic reaction will be exhibited in the conversion of benzocyclobutenes to o-quinodimethanes.