Mechanistic investigations into the Pauson-Khand reaction: Using descriptor-based methods and in-situ IR spectroscopy for mechanistic insight Theo Tanner, John Slattery, Jason Lynam, Ian J. S. Fairlamb University of York, UK The Pauson-Khand reaction (PKR), discovered in the 1970s 1 , presents a method for the efficient cyclisation of an alkyne and an alkene in the presence of a cobalt carbonyl mediator to form a cyclopentenone. A mechanism for the PKR has been proposed 2 , and currently remains the accepted working theory. However, evidence to support the mechanism is sparse, due to difficulties in observing or trapping intermediates. In this work, a statistical approached based on descriptor-outcome relationship has been applied. A meta-analysis has been performed on published data 3,4 , parameterising alkynes by steric and electronic characteristics, and drawing statistical inferences between these characteristics and the alkynes' activity. The statistical models highlight unexpected behaviour from certain examples of 2-pyridyl-substituted alkynes, leading to unexpected regioselectivity. To further probe this regioselectivity,in-situ FT-IR methods have been used to observe reaction progression, and extract information about cobalt speciation. The observation of the formation of the cobalt tetracarbonyl anion has led to the proposal of alternate speciation pathways for cobalt in the reactive system, which are currently under
investigation References 1. I. U. Khand, G. R. Knox, P. L. Pauson and W. E. Watts, J. Chem. Soc, 1971, 36. 2. P. Magnus and L. M. Principe, Tetrahedron Lett., 1985, 26, 4851.
3. B. E. Moulton, A. C. Whitwood, A. K. Duhme-Klair, J. M. Lynam and I. J. S. Fairlamb, J. Org. Chem., 2011, 76, 5320. 4. E. Fager-Jokela, M. Muuronen, H. Khaizourane, A. Vázquez-Romero, X. Verdaguer, A. Riera and J. Helaja, J. Org. Chem., 2014, 79, 10999.
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