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Solvent-Dependent Divergent Functions of Sc(OTf)3 in Stereoselective Epoxide-Opening Spiroketalizations

Author:
Sharma, Indrajeet, Wurst, Jacqueline M., Tan, Derek S.
Source:
Organic letters 2014 v.16 no.9 pp. 2474-2477
ISSN:
1523-7052
Subject:
Bronsted acids, Lewis acids, alcohols, carbon, catalytic activity, chemical reactions, chemical structure, epoxides, methylene chloride, stereochemistry, stereoselective synthesis, stereoselectivity, thermodynamics
Abstract:
A stereocontrolled synthesis of benzannulated spiroketals has been developed using solvent-dependent Sc(OTf)₃-mediated spirocyclizations of exo-glycal epoxides having alcohol side chains. In THF, the reaction proceeds via Lewis acid catalysis under kinetic control with inversion of configuration at the anomeric carbon. In contrast, in CH₂Cl₂, Brønsted acid catalysis under thermodynamic control leads to retention of configuration. The reactions accommodate a variety of aryl substituents and ring sizes and provide stereochemically diverse spiroketals.
Agid:
5788596