Chiral Primary Amine/Ketone Cooperative Catalysis for Asymmetric α-Hydroxylation with Hydrogen Peroxide
semanticscholar(2020)
Abstract
Carbonyl and amine are yin and yang in organocatalysis
that mutually activate and transform each other. As intrinsically reacting
partners, carbonyl and amine tend to condensate, depleting their individual
activity when employed as catalysts. Though widely established as prominent
catalytic strategies, aminocatalysis and carbonyl catalysis seems not coexist
well and a cooperative amine/carbonyl dual catalysis remains virtually unknown.
Here we report a cooperative primary amine and ketone dual catalysis in the
asymmetric α-hydroxylation with H2O2. Besides
participating in the typical enamine catalytic cycle, the chiral primary amine
catalyst was found to work cooperatively with a ketone catalyst to activate H2O2
via an oxaziridine intermediate
derived from in-situ generated ketimine intermediate. The resulted
enamine-oxaziridine coupling then facilitated highly-controlled hydroxylation
of β-ketocarbonyls that are not possible with other catalytic methods. The
dual catalytic approach allows for highly enantioselective α-hydroxylation
of a broad range of β-ketocarbonyls. Particularly, late-stage
hydroxylation for peptidyl amide or chiral esters can also be achieved with
high stereoselectivity. With its operational simplicity and mild conditions, this
cooperative amine/ketone catalysis provides a new strategy in catalytic
activation of H2O2 and expands the domain of typical
amine and carbonyl catalysis to include those challenging transformations.
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