Pauson–Khand reaction

From Wikipedia, the free encyclopedia
Jump to navigation Jump to search
Pauson–Khand reaction
Named after Peter Ludwig Pauson
Ihsan Ullah Khand
Reaction type Ring forming reaction
Organic Chemistry Portal pauson-khand-reaction
RSC ontology ID RXNO:0000464

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] The reaction was discovered by Ihsan Ullah Khand (1935-1980), who was working as a postdoctoral associate with Peter Ludwig Pauson (1925-2013)[3] 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.[4][5] 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.[6]

PK reaction

With unsymmetrical alkenes or alkynes, regioselectivity can be problematic, but less so with intramolecular reactions.[7]

PK reaction example

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.[8]


Wilkinson's catalyst, based on the transition metal rhodium, also effectively catalyses PK reactions but requires silver triflate as a co-catalyst.[9]

PK reaction with Wilkinson's catalyst

Molybdenum hexacarbonyl is a carbon monoxide donor in PK-type reactions between allenes and alkynes with dimethyl sulfoxide in toluene.[10]

PK reaction with molybdenum hexacarbonyl

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).[11]

Pauson Khand reaction Seigal 2005

See also[edit]


  1. ^ P. L. Pauson and I. U. Khand. Ann. N. Y. Acad. Sci. 1977, 295, 2.
  2. ^ Blanco-Urgoiti, J.; Añorbe, L.; Pérez-Serrano, L.; Domínguez, G.; Pérez-Castells, J. Chem. Soc. Rev. 2004, 33, 32. doi:10.1039/b300976a
  3. ^ H. Werner. Angew. Chem. Int. Ed. 2014, 53, 3309. doi:10.1002/anie.201400432
  4. ^ Schore, N. E. "The Pauson–Khand Cycloaddition Reaction for Synthesis of Cyclopentenones" Org. React., 1991, 40, 1. doi:10.1002/0471264180.or040.01
  5. ^ 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
  6. ^ 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 4833603Freely accessible. 
  7. ^ 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. 
  8. ^ Strategic applications of named reactions in organic synthesis: background and details mechanisms 2007 László Kürti,Barbara Czakó
  9. ^ 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)
  10. ^ 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. 
  11. ^ 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