An asymmetric approach to bicyclo[2.2.1]heptane-1-carboxylates via a formal [4 + 2] cycloaddition reaction enabled by organocatalysis

Fu, Jian‐Guo; Shan, Yifan; Sun, Weidong; Lin, Guo‐Qiang; Sun, Bing

doi:10.1039/c6ob00814c

Cited by 9 publications

(3 citation statements)

References 26 publications

(7 reference statements)

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“…The previously not available endo product was obtained with an ee of 98 %. Prior to this study, only the exo isomer of 11 was accessible with moderate dr by chiral amine catalysis with TONs <20 [24, 25] …”

Section: Methodsmentioning

confidence: 99%

“…Prior to this study, only the exo isomer of 11 was accessible with moderate dr by chiral amine catalysis with TONs < 20. [24,25] To learn more about the role of the aprotic betaine, experiments with several control catalysts were conducted (Table 4). Cs 2 CO 3 (2.5 mol %) in the absence of a Cu complex formed racemic product 3 aB in 95 % yield as an endo/exo mixture (84:16).…”

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confidence: 99%

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

et al. 2020

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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 imidazoliumaryloxide 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.

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Section: Methodsmentioning

confidence: 99%

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confidence: 99%

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

et al. 2020

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“…[74] As identified by Sherburn and coworkers, this retrosynthetic disconnection of the aglycone via its 1,2-diketone tautomer 59 formally represents a DA reaction between diene 56 and ethylene dione (60), a reagent for which a synthetic equivalent has yet to be developed. Although not yet realized, there is opportunity for an enantioselective sequence incorporating nitroalkenes as masked ketenes, as enantioselective DA reactions of nitroethylene [75] and substituted derivatives [76,77] are known.…”

Section: Nitroalkenesmentioning

confidence: 99%