Phosphine-catalyzed synthesis of 6-substituted 2-pyrones: Manifestation of E/Z-isomerism in the zwitterionic intermediate
XF Zhu, AP Schaffner, RC Li, O Kwon
Index: Zhu, Xue-Feng; Schaffner, Arnaud-Pierre; Li, Ronald C.; Kwon, Ohyun Organic Letters, 2005 , vol. 7, # 14 p. 2977 - 2980
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Citation Number: 133
Abstract
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 ...
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