Preparation of Methoxy-Substituted Optically Active 7-Alkoxycarbonylcycloheptatrienes and Their Acid-Promoted Rearrangements

Four optically active cycloheptatriene derivatives carrying a methoxy group(s) at different positions were prepared by the 2,4-pentanediol-tethered Buchner reaction. In addition to the high stereoselectivity, the tetheralso controlled the regioselectivity in a good-to-high degree. Some of the products are unstable under acidic conditions, resulting in isomerization through a prototropic reaction or aromatization. The Bronsted acid promoted prototropic isomerization by regio-and stereoselective protonation and ensuing deprotonation, while the Lewis acid-catalyzed reaction provided an aromatized product via the norcaradiene tautomer.