Nitrone and Alkyne Cascade Reactions for Regio- and Diastereoselective 1-Pyrroline Synthesis
Guanqun Zhang1, Abdullah S Alshreimi1, Laura Alonso1
1Department of Chemistry, University of Illinois at Chicago, 845 W Taylor St. MC 111, Chicago, IL, 60607, USA.
Abstract:
The synthesis of 1-pyrrolines from N-alkenylnitrones and alkynes has been explored as a retrosynthetic alternative to traditional approaches. These cascade reactions are formal [4+1] cycloadditions that proceed through a proposed dipolar cycloaddition and N-alkenylisoxazoline [3,3']-sigmatropic rearrangement. A variety of cyclic alkynes and terminal alkynes have been shown to undergo the transformation with N-alkenylnitrones under mild conditions to provide the corresponding spirocyclic and densely substituted 1-pyrrolines with high regio- and diastereoselectivity. Mechanistic studies provide insight into the balance of steric and electronic effects that promote the cascade process and control the diastereo- and regioisomeric preferences of the 1-pyrroline products. Diastereoselective derivatization of the 1-pyrrolines prepared by the cascade reaction demonstrate the divergent synthetic utility of the new method.
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