Stereoselective and Regioselective Reaction of Cyclic Ortho Esters with Phenols

Cyclic ortho esters undergo stereoselective and regioselective reaction with phenols when treated with BF3·OEt2 at low temperatures. Attack of the phenol on the ortho ester occurs at an open carbon para to electron-donating groups on the phenol (“C-addition”) or at the phenolic hydroxyl group (“O-ad...

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Bibliographic Details
Published in:Journal of organic chemistry 2001-05, Vol.66 (9), p.3084-3089
Main Authors: Bozell, Joseph J, Miller, Darrin, Hames, Bonnie R, Loveless, Cheryl
Format: Article
Language:English
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Summary:Cyclic ortho esters undergo stereoselective and regioselective reaction with phenols when treated with BF3·OEt2 at low temperatures. Attack of the phenol on the ortho ester occurs at an open carbon para to electron-donating groups on the phenol (“C-addition”) or at the phenolic hydroxyl group (“O-addition”) depending on the nature of the cation formed from reaction of the ortho ester and BF3·OEt2. Products resulting from O-addition undergo reversion to a mixture of starting phenol, C-addition product, and O-addition product if treated with BF3·OEt2 at room temperature, but C-addition products are stable under the same conditions. X-ray structural analysis of the C-addition compound indicates that its stereochemistry is opposite to that observed in reaction of similar ortho esters with chloride from TMSCl. However, the stereochemistry of the reaction can be rationalized by the ability of the ortho ester to isomerize via an intermediate benzylic cation and examination of the preferred trajectory of attack of the nucleophile on the intermediate oxonium ion.
ISSN:0022-3263
1520-6904
DOI:10.1021/jo005736t