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Anion-Ļ€ catalysis: Bicyclic products with four contiguous stereogenic centers from otherwise elusive diastereospecific domino reactions on Ļ€-acidic surfaces
JournalArticle (Originalarbeit in einer wissenschaftlichen Zeitschrift)
ID
4196630
Author(s)
Liu, Le; Cotelle, Yoann; Klehr, Juliane; Sakai, Naomi; Ward, Thomas R.; Matile, Stefan
Anion-Ļ€ catalysis: Bicyclic products with four contiguous stereogenic centers from otherwise elusive diastereospecific domino reactions on Ļ€-acidic surfaces
Journal
Chemical Science
Volume
8
Number
5
Pages / Article-Number
3770-3774
Abstract
Anionā€“Ļ€ interactions have been introduced recently to catalysis. The idea of stabilizing anionic intermediates and transition states on Ļ€-acidic surfaces is a new fundamental concept. By now, examples exist for asymmetric enolate, enamine, iminium and transamination chemistry, and the first anionā€“Ļ€ enzyme has been created. Delocalized over large aromatic planes, anionā€“Ļ€ interactions appear particularly attractive to stabilize extensive long-distance charge displacements during domino processes. Moving on from the formation of cyclohexane rings with five stereogenic centers in one step on a Ļ€-acidic surface, we here focus on asymmetric anionā€“Ļ€ catalysis of domino reactions that afford bicyclic products with quaternary stereogenic centers. Catalyst screening includes a newly synthesized, better performing anionā€“Ļ€ version of classical organocatalysts from cinchona alkaloids, and anionā€“Ļ€ enzymes. We find stereoselectivities that are clearly better than the best ones reported with conventional catalysts, culminating in unprecedented diastereospecificity. Moreover, we describe achiral salts as supramolecular chirality enhancers and report the first artificial enzyme that operates in neutral water with anionā€“Ļ€ interactions, i.e., interactions that are essentially new to enzymes. Evidence in support of contributions of anionā€“Ļ€ interactions to asymmetric catalysis include increasing diastereo- and enantioselectivity with increasing rates, i.e., asymmetric transition-state stabilization in the presence of Ļ€-acidic surfaces and inhibition with the anion selectivity sequence NO3āˆ’ > Brāˆ’ > BF4āˆ’ > PF6āˆ’.
