Total Synthesis of (+)-Hyacinthacine A2 Based on SmI2-Induced Nitrone Umpolung
journal contributionposted on 18.02.2005 by Stéphanie Desvergnes, Sandrine Py, Yannick Vallée
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A concise total synthesis of (+)-hyacinthacine A2, a polyhydroxylated pyrrolizidine alkaloid, is described using our recently discovered inversion of the C−N bond polarity in nitrones. In the key step, the diastereoselective reductive coupling of a l-xylose-derived cyclic nitrone with ethyl acrylate allowed the assembly of the bicyclic core of the target molecule, by way of a tandem formation of the C−C and C−N bonds. The method opens a novel, short, and general route for the synthesis of other pyrrolizidine alkaloids.