AI Article Synopsis
- This paper examines the balance between a phosphonium dienolate zwitterion and a vinylogous phosphorus ylide, detailing their interactions with aldehydes.
- The reactions with ethyl 2-methyl-2,3-butadienoate depend on the presence of a Lewis acid and the type of phosphine used, leading to different intermediates.
- A unique vinylogous Wittig olefination was observed with electron-deficient aromatic aldehydes when coupled with specific phosphines and Lewis acids, while triphenylphosphine without a Lewis acid promoted a vinylogous aldol addition and a rare phosphorus-to-carbon migration.
Article Abstract
This paper describes the equilibrium established between a phosphonium dienolate zwitterion and a vinylogous phosphorus ylide, and their reactions with aldehydes. The reactions between ethyl 2-methyl-2,3-butadienoate and various aldehydes occur through either a phosphonium dienolate or a vinylogous ylide intermediate, depending on the presence/absence of a Lewis acid and the nature of the phosphine. We observed a rare vinylogous Wittig olefination from the reaction between ethyl 2-methyl-2,3-butadienoate and an electron-deficient aromatic aldehyde in the presence of a stoichiometric amount of an electron-deficient triarylphosphine and a catalytic amount of a Lewis acid (e.g., BF(3)·Et(2)O). On the other hand, the use of triphenylphosphine, in the absence of a Lewis acid, facilitated vinylogous aldol addition, accompanied by a rare 1,2-aryl phosphorus-to-carbon migration.
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| http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3043383 | PMC |
| http://dx.doi.org/10.1016/j.tet.2010.03.044 | DOI Listing |
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Article Synopsis
- This paper examines the balance between a phosphonium dienolate zwitterion and a vinylogous phosphorus ylide, detailing their interactions with aldehydes.
- The reactions with ethyl 2-methyl-2,3-butadienoate depend on the presence of a Lewis acid and the type of phosphine used, leading to different intermediates.
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Theory-Guided Design of Brønsted Acid-Assisted Phosphine Catalysis: Synthesis of Dihydropyrones from Aldehydes and Allenoates.
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Department of Chemistry and Biochemistry, University of California, Los Angeles 607 Charles E. Young Drive East, Los Angeles, California 90095-1569.
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-phosphonium dienolates toward the s-cis intermediate was accomplished through the use of a Brønsted acid additive, which disrupts the favorable Coulombic interaction present in the s-trans intermediate. The detailed nature of the synergistic interactions involving the Brønsted acid additives and phosphine involved in the formation of s-cis beta-phosphonium dienolates was analyzed through a series of DFT calculations.
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