Enantiodivergent [4+2] Cycloaddition of Dienolates by Polyfunctional Lewis Acid/Zwitterion Catalysis

Diels–Alder reactions have become established as one of the most effective ways to prepare stereochemically complex six‐membered rings. Different catalysis concepts have been reported, including dienophile activation by Lewis acids or H‐bond donors and diene activation by bases. Herein we report a n...

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Bibliographic Details
Published in:Angewandte Chemie International Edition 2020-11, Vol.59 (45), p.19873-19877
Main Authors: Miskov‐Pajic, Vukoslava, Willig, Felix, Wanner, Daniel M., Frey, Wolfgang, Peters, René
Format: Article
Language:English
Subjects:
Acidification
asymmetric catalysis
Catalysis
Catalysts
Communication
Communications
Cooperative control
Cycloaddition
Diels–Alder cycloaddition
Enantiomers
Hydrogen bonding
Hydrogen bonds
lactams
lactones
Lewis acid
Maleic anhydride
Mode of action
polyfunctional catalysts
Zwitterions
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Summary:Diels–Alder reactions have become established as one of the most effective ways to prepare stereochemically complex six‐membered rings. Different catalysis concepts have been reported, including dienophile activation by Lewis acids or H‐bond donors and diene activation by bases. Herein we report a new concept, in which an acidic prodiene is acidified by a Lewis acid to facilitate deprotonation by an imidazolium–aryloxide entity within a polyfunctional catalyst. A metal dienolate is thus formed, while an imidazolium–ArOH moiety probably forms hydrogen bonds with the dienophile. The catalyst type, readily prepared in few steps in high overall yield, was applied to 3‐hydroxy‐2‐pyrone and 3‐hydroxy‐2‐pyridone as well as cyclopentenone prodienes. Maleimide, maleic anhydride, and nitroolefin dienophiles were employed. Kinetic, spectroscopic, and control experiments support a cooperative mode of action. High enantioselectivity was observed even with unprecedented TONs of up to 3680. In an efficient approach to catalytic asymmetric [4+2] cycloaddition, acidic prodienes were deprotonated by a betaine species to form a copper dienolate, and the dienophile was activated by hydrogen‐bond formation (see scheme). The polyfunctional catalyst promoted the transformation with high enantioselectivity as well as high turnover numbers.
ISSN:1433-7851
1521-3773
DOI:10.1002/anie.202009093