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Enantioselective Nazarov Reactions through Catalytic Asymmetric Proton Transfer

Guangxin Liang and Dirk Trauner*

*Center for New Directions in Organic Synthesis, Department of Chemistry, University of California, Berkeley, California 94720-1460, Email: traunercchem.berkeley.edu

G. Liang, D. Trauner, J. Am. Chem. Soc., 2004, 126, 9544-9545.

DOI: 10.1021/ja0476664


Abstract

A catalytic asymmetric Nazarov reaction is described that requires only 10 mol % of a chiral Lewis acid and proceeds with ee's between 72% and 97%.

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Details

The document discusses the development of enantioselective Nazarov reactions through catalytic asymmetric proton transfer. Nazarov cyclizations, known since the 1940s, involve a complex mechanism and have only recently seen the emergence of catalytic asymmetric variants. The authors, Guangxin Liang and Dirk Trauner, from the University of California, Berkeley, have developed 2-alkoxy-1,4-pentadien-3-ones as substrates for these cyclizations, allowing for bidendate coordination of a chiral Lewis acid. They report the use of scandium-pybox complexes in acetonitrile with molecular sieves, achieving high yields and enantioselectivities. The study highlights the challenges of optimizing these reactions, including low yields and sensitivity to substrate variations. However, substrates lacking a terminal substituent provided consistent results. The absolute configuration of the products was established through X-ray crystallography. The authors acknowledge financial support from Glaxo Smith Kline, Eli Lilly, and Merck & Co. and provide supporting information online. This work represents the first truly catalytic asymmetric Nazarov reactions with high enantioselectivity, paving the way for further exploration of catalytic asymmetric proton-transfer reactions in organic synthesis.


Key Words

Enones, Nazarov Cyclization


ID: J48-Y2005-2430