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

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
Faculty:	Science and Technology (TNW)
Research Group:	Molecular Nanofabrication (MNF)
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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