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The Pauson–Khand reaction (or PKR or PK-type reaction) is a chemical reaction described as a [2+2+1] cycloaddition between an alkyne, an alkene and carbon monoxide to form a α,β-cyclopentenone.[1][2] This reaction was originally mediated by stoichiometric amounts of dicobalt octacarbonyl, but this has since been replaced by newer and more efficient catalyst systems.[3][4]
With asymmetrical alkenes or alkynes regioselectivity is always an issue, but less so with intramolecular reactions [5].
The reaction works with both terminal and internal alkynes although internal alkynes tend to give lower yields. The order of reactivity for the alkene is strained cyclic alkene > terminal alkene > disubstituted alkene > trisubstituted alkene. Unsuitable alkenes are tetrasubstituted alkenes and alkenes with strongly electron withdrawing groups. [6]
Variations[edit]
Wilkinson's catalyst, based on the transition metal rhodium, also effectively catalyses PK reactions but requires silver triflate as a co-catalyst [7].
Molybdenum hexacarbonyl is a carbon monoxide donor in PK-type reactions between allenes and alkynes with dimethyl sulfoxide in toluene [8].
Cyclobutadiene also lends itself to a [2+2+1] cycloaddition although this reactant is generated in situ from decomplexation of stable cyclobutadiene iron tricarbonyl with CAN. [9]
See also[edit]
References[edit]
- ^ P. L. Pauson and I. U. Khand. Ann. N.Y. Acad. Sci. 1977, 295, 2.
- ^ Blanco-Urgoiti, J.; Añorbe, L.; Pérez-Serrano, L.; Domínguez, G.; Pérez-Castells, J. Chem. Soc. Rev. 2004, 33, 32. doi:10.1039/b300976a
- ^ Schore, N. E. Org. React., 1991, 40, 1. (doi:10.1002/0471264180.or040.01)
- ^ S. E. Gibson and A. Stevenazzi, Angew. Chem. Int. Ed., 2003, 42, 1800-1810. doi:10.1002/anie.200200547
- ^ Jeong, Nakcheol; Hwang, Sung Hee; Lee, Youngshin; Chung, Young Keun (1994). "Catalytic version of the Intramolecular Pauson-Khand Reaction". Journal of the American Chemical Society. 116 (7): 3159. doi:10.1021/ja00086a070.
- ^ Strategic applications of named reactions in organic synthesis: background and details mechanisms 2007 László Kürti,Barbara Czakó
- ^ Pauson–Khand-type reaction mediated by Rh(I) catalysts Nakcheol Jeong, Byung Ki Sung, Jin Sung Kim, Soon Bong Park,Sung Deok Seo, Jin Young Shin, Kyu Yeol In, and Yoon Kyung Choi Pure Appl. Chem., Vol. 74, No. 1, pp. 85–91, 2002. (Online article)
- ^ Kent, J (1995). "A new allenic Pauson-Khand cycloaddition for the preparation of α-methylene cyclopentenones". Tetrahedron Letters. 36 (14): 2407–2410. doi:10.1016/0040-4039(95)00315-4.
- ^ Intramolecular [2+2+1] Cycloadditions with (Cyclobutadiene)tricarbonyliron Benjamin A. Seigal, Mi Hyun An, Marc L. Snapper Angewandte Chemie International Edition Volume 44, Issue 31 , Pages 4929 - 4932 2005. doi:10.1002/anie.200501100
Category:Cycloadditions
Category:Multiple component reactions
Category:Name reactions