Mechanism of cis-enamide formation from N-(alpha-silyl)allyl amides: synthetic potential of stepwise dyotropic rearrangements |
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Authors: | Zhang Xiyun Houk K N Lin Songnian Danishefsky Samuel J |
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Institution: | Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, USA. |
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Abstract: | A novel transformation of silyl amides to N-cis-propenyl amides was recently reported, the reaction of which is a formal 10-electron double sigmatropic, or dyotropic, rearrangement. Density functional calculations (B3LYP/6-311++G(3d,3p)//B3LYP/6-31G(d)) have been carried out to investigate the mechanism of this reaction. A two-step process involving sequential 1,4-silyl and 1,4-hydrogen shifts is predicted. The 1,3-dipolar azomethine ylide intermediate profits from charge stabilization by allylic resonance and phenyl conjugation. The consecutive thermal migration of two sigma-bonds (stepwise dyotropic rearrangement) is an example of a host of reactions with synthetic potential. |
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