Synthesis of pyrrolizines by intramolecular capture of 1,4-dipolar intermediates in reactions of enamines with dimethyl acetylenedicarboxylate

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Verboom, W. and Visser, G.W. and Trompenaars, W.P. and Reinhoudt, D.N. and Harkema, S. and Hummel van, G.J. (1981) Synthesis of pyrrolizines by intramolecular capture of 1,4-dipolar intermediates in reactions of enamines with dimethyl acetylenedicarboxylate. Tetrahedron, 37 (20). pp. 3525-3533. ISSN 0040-4020

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Abstract:Solvent polarity and reaction temperature strongly influence the reactions of dimethyl acetylenedicar-boxylate (DMAD) with 1-pyrrolidinyl enamines of acyclic and cyclic ketones. Whereas DMAD and 1-[1-phenyl-2-(phenylthio)ethenyl]pyrrolidine (3) give only a mixture of the isomeric 1,3-butadienes (5) in apolar solvents, in methanol the main product is the pyrrolizine 7, together with 5. Again in methanol, DMAD reacts at 0-5° with 8, 9 and 10 to give exclusively 1:1 adducts, the pyrrolizines 11,12 and 13, respectively, whereas at −50° 8 and 9 give 1:2 (enamine : DMAD) adducts, the pyrrolizines 14 and 15, respectively; a single crystal X-ray analysis of 14 gave the structure of the 1:2 adducts. In the same solvent methyl propiolate and 8 give only the linear Michael adduct 17. The enamine-ketone 18 reacts with DMAD in propylene carbonate at 0–5° to give, via (2 + 2)-cycloaddition and ring expansion, 19, and the linear Michael adduct 20. The mechanism of (2 + 2)-cycloaddition and pyrrolizine formation is discussed in terms of a common tied-ion pair intermediate formed in the first, rate-determining step, followed by a second solvent-dependent step.
Item Type:Article
Copyright:© 1981 Elsevier Science
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Science and Technology (TNW)
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Link to this item:http://purl.utwente.nl/publications/68773
Official URL:http://dx.doi.org/10.1016/S0040-4020(01)98870-2
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