Toward the understanding of the mechanism and enantioselectivity
of the PausonKhand reaction. Theoretical and experimental studies*
Miquel A. Pericàs, Jaume Balsells, Jaume Castro, Iolanda Marchueta,
Albert Moyano, Antoni Riera, Jordi Vázquez, and Xavier Verdaguer
Unitat de Recerca en Síntesi Asimètrica,
Departament de Química Orgànica, Universitat de Barcelona,
E-08028 Barcelona, Spain
Abstract: Semiempirical and density functional theory (DFT)
calculations have been performed on the key steps of the commonly accepted
mechanism of the PausonKhand reaction (PKR). In this context,
the high reactivity of ynamine complexes in the cycloaddition process
has been rationalized on the basis of an anomerically assisted dissociation
of CO. Moreover, an explanation has been provided for the correlation
between olefin strain and reactivity in the PKR. Inspired by these results,
new selective syntheses of cyclopentanones and phenols based on PKR
with cyclopropene have been developed. On the other hand, the theoretical
analysis of phosphine-substituted dicobalt carbonyl complexes of alkynes
has helped in the development of efficient chelating (P,N) and bridging
(P,S) ligands for the stereochemical control of the reaction and in
the understanding of their action modes.
*Lecture presented at the 11th IUPAC International
Symposium on Organometallic Chemistry Directed Towards Organic Synthesis
(OMCOS-11), Taipei, Taiwan, 22-26 July 2001. Other presentations are
presented in this issue, pp.1-186.
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