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[摘要]：Sigmatropic rearrangement of tetrahydropyridine-derived ammonium is a valuable method for the prepn. of substituted prolines. For example, azabicyclo[3.3.0]octene I was treated with BrCH2CO2Me in DMF at -15? followed by treatment with NaH in presence of 4?mol. sieves, to give substituted proline II in 34% yield. This reaction proceeded by [2,3]-sigmatropic rearrangement of a bicyclic tetrahydropyridine-derived ammonium ylid, where the extra rigidity of the azabicyclo[3.3.0]octene system preorganizes the transition state and lowers the activation energy for rearrangement. |
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