Enantiopure exo-4-nitro-3,5-diphenylproline reacts with aldehydes and electrophilic alkenes,
in good yields, through a multicomponent 1,3-dipolar cycloaddition where the intermediate azomethine
ylide is generated by the decarboxylative route. The reactions with maleimides afford diastereoselectively
nitropyrrolizidines. Dimethyl fumarate and 1,2-bis(phenylsulfonyl)ethylene also give variable
mixtures of diastereoisomeric nitropyrrolizidines. The replacement of aldehydes by phenyl-3-buten-2-
one also affords satisfactory results with high diastereoselection although in lower yields. The stereochemical
outcome is studied and defined according to the absolute configuration of the resulting cycloadducts.
Keywords: Pyrrolizidine, nitroprolinates, cycloaddition, azomethine ylides, decarboxylation, multicomponent.
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