Enantiodivergent [4+2] Cycloaddition of Dienolates by Polyfunctional Lewis Acid/Zwitterion Catalysis
| Autor: | Wolfgang Frey, Vukoslava Miskov‐Pajic, Daniel M. Wanner, Felix Willig, René Peters |
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| Rok vydání: | 2020 |
| Předmět: |
Asymmetric Catalysis
Diels–Alder cycloaddition Diene 010405 organic chemistry Communication Maleic anhydride General Medicine General Chemistry polyfunctional catalysts 010402 general chemistry 01 natural sciences Communications Catalysis Cycloaddition lactones 0104 chemical sciences chemistry.chemical_compound Deprotonation chemistry Zwitterion Organic chemistry lactams Lewis acids and bases Maleimide |
| Zdroj: | Angewandte Chemie (International Ed. in English) |
| ISSN: | 1521-3773 1433-7851 |
| DOI: | 10.1002/anie.202009093 |
| Popis: | 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. |
| Databáze: | OpenAIRE |
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