Pauson

KHAND PAUSON Cyclopentenone Annulat/on Cyclopentenone synthesis from cartxin monoxide acetylene and olefins, cobalt carbonyl catalyzed. 

The methods of preparation of ferrocene have been reviewed by Pauson and by Fischer. Ferrocene has been made by the reaction of ferric chloride with cyclopentadienylmagnesium bromide, by the direct thermal reaction of cyclopentadiene with iron metal, by the direct interaction of cyclopentadiene with iron carbonyl, by the reaction of ferrous chloride with cyclopentadiene in the presence of organic bases such as diethyl-amine, by the reaction of ferrous chloride with sodium cyclo-[lentadienide in liquid ammonia, and from cyclopentadiene and... 

This procedure is based on the method of Lindsay and Hauser as modified slightly by Osgerby and Pauson. N,N-dimethyl-aminomethylferrocene methiodide has also been prepared by heating formylferrocene with dimethylamine and hydrogen in the presence of Raney nickel catalyst to give dimethylamino-methylferrocene, which was quaternized with methyl iodide. ... 

Asymmetric Pauson-Khand reaction in syntheses of heterocycles fused with five-member carbocyclic fragment 980PP121. 

The reaction of an alkyne 1 and an alkene 2 in the presence of dicobaltoctacar-bonyl to yield a cyclopentenone 3 is referred to as the Pauson-Khand reaction Formally it is a [2 + 2 + 1 ]-cycloaddition reaction. The dicobaltoctacarbonyl acts as coordinating agent as well as a source of carbon monoxide. 

An example for the synthetic potential is the formation of a fenestrane skeleton 11 from the open-chain compound 10 by a cascade of two consecutive intramolecular Pauson-Khand reactions, the yield in this case is however only 9% J... 

The Pauson-Khand reaction was originally developed using strained cyclic alkenes, and gives good yields with such substrates. Alkenes with sterically demanding substituents and acyclic as well as unstrained cyclic alkenes often are less suitable substrates. An exception to this is ethylene, which reacts well. Acetylene as well as simple terminal alkynes and aryl acetylenes can be used as triple-bond component. 

RCM of 132 to the medium-sized enyne 135, for example, appears to be highly unlikely. This transformation was achieved by conversion of 132 to the cobalt complex 133, which is cyclized to the protected cycloenyne 134. Deprotection yields 135, and a subsequent Pauson-Khand reaction yields the interesting tricyclic structure 136 (Scheme 27) [125c]. 

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