Enantioselektive Synthese von γ‐Aminosäure‐Derivate: Die Umpolung der CN‐Bindung von Nitronen gelingt durch Reduktion mit SmI2. Auf diese Weise gebildete Spezies addieren unter milden Bedingungen mit exzellenter Stereoselektivität an α,β‐ungesättigte Ester. Man erhält γ‐N‐Hydroxyaminoester (siehe Schema).
The zinc-mediated reduction of nitroalkanes and nitroarenes in the presence of aldehydes is an efficient method to synthesize a wide range of nitrones. This method is mild enough to accommodate a variety of functional groups. It is particularly useful when the intermediate hydroxylamines are unstable and/or watersoluble. We used it to prepare several aromatic, aliphatic and highly functionalized sugar-derived nitrones.
α,α-Disubstituted piperidines and conformationally constrained polyhydroxylated indolizidines bearing a hydroxymethyl substituent in position 8a were synthesized from a readily available l-sorbose-derived ketonitrone. Diastereoselective vinylation under two sets of complementary conditions allowed access to both configurations of the newly formed quaternary stereocenter. Subsequent N-allylation and ring-closing metathesis afforded 8a-branched indolizidines in high yield. The newly prepared iminosugars demonstrated highly potent inhibition of α-glucosidases. Most interestingly, compound 9b exhibits very high selectivity toward this class of enzymes, with an unusual mode of binding.
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