期刊
TETRAHEDRON
卷 64, 期 29, 页码 6935-6942出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.tet.2008.04.075
关键词
phosphine; catalysis; Lewis base; Bronsted acid; dihydropyrone; aldehyde; allenoate
The phosphine-catalyzed addition of 2,3-butadienoates to aldehydes has been extended to the formation of disubstituted dihydro-2-pyrones. The requisite shift in equilibrium of the intermediate zwitterionic beta-phosphomuin dienolates toward the s-cis intermediate was accomplished through the use of a Bronsted acid additive, which disrupts the favorable Coulombic interaction present in the s-trans intermediate. The detailed nature of the synergistic interactions involving the Bronsted acid additives and phosphine involved in the formation of s-cis beta-phosphonium dienolates was analyzed through a series of DFT calculations. Unlike previously reported annulations of aldehydes with allenoates, where trialkylphosphines are optimal catalysts, in this study triphenylphosphine was also found for the first time to be a suitable catalyst for the synthesis of dihydropyrones. This method provides a one-step route toward functionalized dihydropyrones from simple, stable starting materials. In addition, new reaction pathways of phosphine-catalyzed allene annulations are unveiled, with the formation of dihydropyrones being the first example of dual activation in this sphere. (C) 2008 Elsevier Ltd. All rights reserved.
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