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The use of ethylene glycol (15% v/v in toluene) as additive in the catalytic Pauson-Khand reaction (PKR) is reported. In most cases both the yield and selectivity were enhanced compared to standard protocols. Moreover, the immiscibility of ethylene glycol in toluene allowed recycling of the catalyst (which remained mainly in the ethylene glycol). The recycling allowed catalyst loading to be reduced to only 3 mol%. A gram-scale reaction was also performed, allowing the use of only 1 mol% of Co2(CO)8, the lowest amount reported so far in intermolecular cobalt-catalyzed PKR. [ABSTRACT FROM AUTHOR]

The use of ethylene glycol as additive in the N-oxide-promoted intermolecular Pauson-Khand reaction (PKR) has been studied. The addition of 15% ethylene glycol to the reaction mixture consistently increased (from 20% up to 2-4-fold) the reaction yields. [ABSTRACT FROM AUTHOR]

The scope of the Pauson-Khand reaction (PKR) of internal trifluoromethyl alkynes, previously described with norbornadiene, is expanded to norbornene and ethylene. A thorough structural analysis of the resulting PK adducts has been carried out to unveil that α-trifluoromethylcyclopentenones are preferred in all cases, independently of the electronic properties of the alkyne. The regioselectivity observed with norbornadiene and ethylene is higher than in the case of norbornene. [ABSTRACT FROM AUTHOR]

A synthetic approach to the methyl esters of Prostaglandin B1 and Phytoprostanes 16-B1-PhytoP (PPB1-I) and 9-L1-PhytoP (PPB1-II) based on the modified Julia olefination of a formylcyclopentenone and an appropriately protected hydroxy sulfone has been developed. The cyclopentenones were efficiently prepared by intermolecular Pauson-Khand reaction of a (silyloxymethyl)alkyne. The sulfone counterpart was prepared by regioselective ring-opening of the appropriate chiral epoxides by 2-mercaptobenzothiazole. The protecting group for the alcohol functionality on the sulfone proved to be crucial. Protection as a tert-butyl ether was the best solution, giving better results than a tert-butyldimethylsilyl ether. [ABSTRACT FROM AUTHOR]

The article discusses how the Pauson-Khand cycloaddition reaction builds the tetracyclic core of (+)-ryanodol. Topics covered include the Pauson-Khand reaction generating three new carbon bonds as it forms a cyclopentenone in one step, the synthesis of anxinellamines reflecting the versatility of the cyclopentenone core, and the need for increasing the range of olefins that can be efficiently cyclized.

A new approach to the synthesis of 4,5-disubstituted cyclopentenones is described. The strategy is based on the Pauson–Khand (PK) reaction of norbornadiene and N-Boc-propargylamine as an alkyne with a masked leaving group, which can be eliminated at will. This approach to the synthesis of 4,5-disubstituted cyclopentenones overcomes the problem of using the alkylation to introduce the α side chain. As an example, prostane 13-epi-12-oxo-phytodienoic acid (13-epi-12-oxo-PDA) methyl ester was synthesized. [ABSTRACT FROM AUTHOR]

Abstract: Herein we describe the synthesis and structure of a new chiral bidentate P,S(O) ligand containing a stereogenic sulfur atom. We also report on its coordination properties to acetylene dicobalt hexacarbonyl complexes, providing X-ray structures of the ligand alone and of a ligand–cobalt complex. Solid state structure of complex 4 shows the formation of a weak C–H⋯O bond between a polarised methine group in the ligand and a sulfone group on the alkyne that helps to stabilize the bridged coordination mode. [Copyright &y& Elsevier]

The asymmetric intermolecular andcatalytic Pauson–Khandreaction has remained an elusive goal since Khand and Pauson discoveredthis transformation. Using a novel family of P-stereogenic phosphanes,we developed the first catalytic system with useful levels of enantioselectionfor the reaction of norbornadiene and trimethylsilylacetylene. Theresults demonstrate that Co–bisphosphane systems are sufficientlyreactive and that they lead to high selectivity in the intermolecularprocess. [ABSTRACT FROM AUTHOR]

Generally judged poor electronic regioselectivity of alkyne insertion in intermolecular Pauson-Khand reaction (PKR) has severely restricted its synthetic applications. In our previous rational study concerning diarylalkynes (Fager-Jokela, E.; Muuronen, M.; Patzschke, M.; Helaja, J. J. Org. Chem. 2012, 77, 9134- 9147), both experimental and theoretical results indicated that purely electronic factors, i.e., alkyne polarization via resonance effect, induced the observed modest regioselectivity. In the present work, we substantiate that the alkyne polarization via inductive effect can result notable, synthetically valuable regioselectivity. Computational study at DFT level was performed to disclose the electronic origin of the selectivity. Overall, the NBO charges of alkynes correlated qualitatively with regioisomer outcome. In a detailed computational PKR case study, the obtained Boltzmann distributions of the transition state (TS) populations correlate closely with experimental regioselectivity. Analysis of the TS-structures revealed that weak interactions, e.g., hydrogen bonding and steric repulsion, affect the regioselectivity and can easily override the electronic guidance. [ABSTRACT FROM AUTHOR]

This protocol is based on the Pauson-Khand reaction of alkynes and norbornadiene yielding masked cyclopentadienones with a readily functionalizable double bond. [ABSTRACT FROM AUTHOR]

1,2,3,4-Tetramethyl-bicyclo[2.2.1]hepta-2,5-diene (TMNBD, for tetramethylnorbornadiene) has been prepared and used successfully as an acetylene equivalent in the synthesis of substituted cyclopentenones. TMNBD is easily accessible on a multigram scale and displays excellent reactivity toward the intermolecular Pauson–Khand reaction. Conjugate additions on the resulting tricyclic compounds proceed with exquisite diastereoselectivity. The retro-Diels–Alder reaction of these TMNBD derivatives occurs under much smoother conditions than those required for its norbornadiene homologues. [ABSTRACT FROM AUTHOR]

A novel family of P-stereogenic diphosphane ligands is developed and applied in the asymmetric cobalt-catalyzed Pauson-Khand reaction. [ABSTRACT FROM AUTHOR]