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. The reaction was discovered by Ihsan Ullah Khand (1935-1980), who was working as a postdoctoral associate with Peter Ludwig Pauson (1925-2013) at the University of Strathclyde in Glasgow. This reaction was originally mediated by stoichiometric amounts of dicobalt octacarbonyl, but newer versions are both more efficient and catalytic. An example of a newer version is the use of [RhCl(CO)2)]2 in the synthesis of (+)-Phorbol by Baran et al. In addition to using a rhodium catalyst this synthesis features an intramolecular cyclization that results in the normal 5-membered α,β-cyclopentenone as well as 7-membered ring.
|Named after||Peter Ludwig Pauson |
Ihsan Ullah Khand
|Reaction type||Ring forming reaction|
|Organic Chemistry Portal|
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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.
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 ceric ammonium nitrate (CAN).
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- S. E. Gibson and A. Stevenazzi "The Pauson–Khand Reaction: the Catalytic Age Is Here!" Angew. Chem. Int. Ed., 2003, 42, 1800-1810. doi:10.1002/anie.200200547
- Kawamura, Shuhei; Chu, Hang; Felding, Jakob; Baran, Phil S. (2016-03-23). "Nineteen-step total synthesis of (+)-phorbol". Nature. 532 (7597): 90–93. Bibcode:2016Natur.532...90K. doi:10.1038/nature17153. ISSN 1476-4687. PMC .
- 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
- Nakcheol Jeong, Byung Ki Sung, Jin Sung Kim, Soon Bong Park,Sung Deok Seo, Jin Young Shin, Kyu Yeol In, Yoon Kyung Choi Pauson–Khand-type reaction mediated by Rh(I) catalysts 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. 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