Application of 1,3-Azomethine Ylides Derived from alpha-Dicarbonyl Compounds and L-Proline to the Synthesis of Pyrrolizidines

[摘要]：The reaction of 2,3-butanedione, ethyl pyruvate, and phenylglyoxal with beta-nitrostyrene and L-proline in isopropanol at room temperature gives substituted pyrrolizidines, as a result of one-pot three component reaction. On the contrary, a spiropyrrolizidine is formed from 1,2-cyclohexanedione only when the reaction is carried out in refluxing isopropanol, whereas at room temperature, incorporation of the amine component into the products is not observed and bicyclo[3.2.1]octanones are formed, as a result of a tandem Michael-Henry reaction. In this latter case, L-proline acts as an organocatalyst, although with modest enantioselectivity. The stereochemistry of the products is given and the mechanism of formation of products is postulated, on the basis of stereochemical arguments.

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