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Categories: C-C Bond Formation > Cyclic compounds > Cyclic enones

Synthesis of cyclopentenones

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Nazarov Cyclization


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A highly efficient catalytic, intermolecular synthesis of the cyclopentane skeleton from simple starting products is reported. Allyl halides, alkynes, and carbon monoxide react under very mild reaction conditions by means of a substoichiometric amount of iron, acetone, and a catalytic amount of Ni(II) iodide.
M. L. Nadal, J. Bosch, J. M. Vila, G. Klein, S. Ricart, J. M. Moretó, J. Am. Chem. Soc., 2005, 127, 10476-10477.


Indanones and 2-cyclopentenones have been successfully prepared in good to excellent yields by the palladium-catalyzed carbonylative cyclization of unsaturated aryl iodides and dienyl triflates, iodides, and bromides, respectively. The mechanism is discussed.
S. V. Gagnier, R. C. Larock, J. Am. Chem. Soc., 2003, 125, 4804-4807.


Conjugated addition of primary nitroalkanes to α,β-unsaturated ketones or α,β-unsaturated esters, in the presence of two equivalents of DBU, allows the one-pot prepration of γ-diketones or γ-keto esters, respectively. The reaction of 2-aryl-1-nitroethane derivatives with α,β-unsaturated ketones gives cyclopentenones.
R. Ballini, L . Barboni, G. Bosica, D. Fiorini, Synthesis, 2002, 2725-2728.


Cyclization of electron-rich 2-alkyl-1-ethynylbenzene derivatives was catalyzed by TpRuPPh3(CH3CN)2PF6 in hot toluene to form 1-substituted-1H-indene and 1-indanone products. The cyclization mechanism involves a 1,5-hydrogen shift of an initial metal-vinylidene intermediate.
A. Odedra, S. Datta, R.-S. Liu, J. Org. Chem., 2007, 72, 3289-3292.


Stirring α,β-unsaturated α-diketones in the presence of activated silica gel results in cyclization to α-hydroxycyclopentenones in good yield. The reaction is sensitive to the mode of stirring and proceeds more rapidly in the presence of triethylamine consistent with a Nazarov reaction proceeding through the enol tautomer.
E. A. Uhrich, W. A. Batson, M. A. Tius, Synthesis, 2006, 2139-2142.


The acid-catalyzed Nazarov reaction of easily accessible β-alkoxy divinyl ketones provides 5-oxycyclopent-2-enones. The effects of the β-alkoxy group on the catalyst efficiency and the regioselectivity are based on the stabilization of the intermediates and the spontaneous elimination of the group followed by trapping.
M. Shindo, K. Yaji, T. Kita, K. Shishido, Synlett, 2007, 1096-1100.


A chiral iridium diphosphine complex catalyzes an enantioselective intramolecular Pauson-Khand-type reaction to give various chiral bicyclic cyclopentenones. A low partial pressure of carbon monoxide is important to achieve excellent enantioselectivity.
T. Shibata, N. Toshida, M. Yamasaki, S. Maekawa, K. Takagi, Tetrahedron, 2005, 61, 9974-9979.


The Rh(I)-catalyzed [3 + 2] cycloaddition of cyclopropenones and alkynes provides a highly efficient and regioselective route to cyclopentadienones (CPDs) that would be otherwise difficult to obtain. The versatility of the method is explored with a wide range of alkynes and diaryl- as well as arylalkylcyclopropenones.
P. A. Wender, T. J. Paxton, T. J. Williams, J. Am. Chem. Soc., 2006, 128, 14814-14815.


An entrapped Rh catalyst derived by a sol-gel process (see article for method), has been used in a Pauson-Khand reaction under mild conditions. The catalyst can be reused at least 10 times without losing activity. This catalytic system is not effective for intermolecular reactions.
K. H. Park, S. U. Song, Y. K. Chung, Tetrahedron Lett., 2003, 44, 2827-2830.