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Lewis Acid Enhancement by Hydrogen-Bond Donors for Asymmetric Catalysis

Lewis Acid Enhancement by Hydrogen-Bond Donors for Asymmetric Catalysis

Steven M Banik, Anna Levina, Alan M Hyde, Eric N Jacobsen

Science. 2017 Nov 10;358(6364):761-764.

PMID: 29123063

Abstract:

Small-molecule dual hydrogen-bond (H-bond) donors such as ureas, thioureas, squaramides, and guanidinium ions enjoy widespread use as effective catalysts for promoting a variety of enantioselective reactions. However, these catalysts are only weakly acidic and therefore require highly reactive electrophilic substrates to be effective. We introduce here a mode of catalytic activity with chiral H-bond donors that enables enantioselective reactions of relatively unreactive electrophiles. Squaramides are shown to interact with silyl triflates by binding the triflate counterion to form a stable, yet highly Lewis acidic, complex. The silyl triflate-chiral squaramide combination promotes the generation of oxocarbenium intermediates from acetal substrates at low temperatures. Enantioselectivity in nucleophile additions to the cationic intermediates is then controlled through a network of noncovalent interactions between the squaramide catalyst and the oxocarbenium triflate.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP180801552	Boc-methoxyphenyldiphenylsulfonium triflate		180801-55-2	Price

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