Phosphine-catalyzed synthesis of 6-substituted 2-pyrones: manifestation of E/Z-isomerism in the zwitterionic intermediate |
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Authors: | Zhu Xue-Feng Schaffner Arnaud-Pierre Li Ronald C Kwon Ohyun |
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Institution: | Department of Chemistry and Biochemistry, University of California, Los Angeles, 90095-1569, USA. |
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Abstract: | reaction: see text] We report a one-step phosphine-catalyzed annulation between aldehydes and ethyl allenoate to form 6-substituted 2-pyrones. The mechanistic rationale for this reaction requires explicit discussion of the E/Z-isomerism of the zwitterionic intermediate formed by the addition of a phosphine to the allenoate. Sterically demanding trialkylphosphines facilitate the shift of equilibrium toward the E-isomeric zwitterion and lead to the formation of 6-substituted 2-pyrones. Various aromatic as well as aliphatic aldehydes undergo the transformation in moderate to excellent yield. |
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