Regiospecific Synthesis of Tetra-Substituted Furans

Abstract

α,β-Unsaturated acetylenic γ-hydroxyketones have been shown to react with ethyl acetoacetate in a Michael-addition fashion and subsequently undergo cyclization followed by dehydration to give substituted furans with a predictable regiospecificity. The yields were good to excellent. A mechanism for the transformation is proposed, and this mechanism explains why furan formation does not take place when the same unsaturated ketones are treated with α-methylated acetoacetate and diethyl malonate.

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GRAPHICAL ABSTRACT

Keywords:

• Conjugated acetylenic ketones
• ketoesters
• propargylic alcohols

ACKNOWLEDGMENTS

Financial support (to L. K. S.) from the Research Council of Norway, through the Research Programme for Catalysis and Synthetic Organic Chemistry (KOSK), and from the Munin Foundation is acknowledged with gratitude. Thanks are also due to the Norwegian Centre for international studies (to I. R. and M. S.) and the Erasmus Programme for scholarships (to F. L.) and to Kazan State Technological University, Kazan, Russia (to I. R.) for financial support. Recording of mass spectra by Terje Lygre and Egil Nodland and, more lately, Bjarte Holmelid, all at the University of Bergen is highly appreciated.

Notes

^a EtMgBr as base.

^b n-BuLi as base.