Beilstein J. Org. Chem.2021,17, 2077–2084, doi:10.3762/bjoc.17.134
of α-substituted glutamates and pyroglutamates via a cyclopropenimine-catalyzed Michael addition of amino ester imines is described. Enantioselectivities of up to 94% have been achieved, and a variety of functional groups were found to be compatible. The impact of the catalyst structure and imine
substitution is discussed. Compared to other methods, this protocol allows for a broader and more enantioselective access to pyroglutamate derivatives.
Keywords: Brønsted base; cyclopropenimine; enantioselective catalysis; Michael addition; pyroglutamate; Introduction
α-Substituted glutamates have value as
strategy for the enanantioselective conjugate addition of amino acid derivatives for this reaction remains an unmet goal.
Our group previously described a chiral cyclopropenimine catalyst that displayed outstanding reactivity for addition reactions of glycine imines [40][41]. We hypothesized that this
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Graphical Abstract
Figure 1:
Strategy for the synthesis of glutamate and pyroglutamate derivatives and several natural products ...