Pauson-Khand reaction Rhodium catalysed

The key step employed a rhodium(l)-catalysed allenic Pauson-Khand reaction to generate the tricyclic ring system 276 from the allenyne 275. However, all attempts to introduced the missing methyl group by a 1,4-addition protocol failed to provide the completed neodolastane framework. Allenyne 275 was synthesized from the enone 274 by a multistep procedure. The quaternary atom was constructed by sequential enolate alkylations. 

Rhodium(I)-catalysed Pauson-Khand reaction of allenynes has been shown to be applicable for constructing azabicyclo[5.3.0]decadienone and oxabicyclo[5.3.0] decadienone frameworks. The 10-monosubstituted-bicyclo[5.3.0] deca-l,7-dien-9-one ring system has been prepared by the rhodium(I)-catalysed Pauson-Khand reaction of allenynes under 10 atm of CO (Scheme 86).129... 

The Pauson-Khand reaction is also mediated by complexes of other transition metals including those of titanium, rhodium and iridium. A number of complexes of these metals have been used to catalyse the intramolecular asymmetric Pauson-Khand reaction of 1,6-enynes to give bicyclo [3.3.0] octenes. The... 

A rhodium-catalysed Pauson-Khand reaction of an allenic alkyne 7.60 was employed to form the cyclopentenone ring of Achalensolide 7.65, a guaianolide natural product (Scheme 7.18). The butenolide ring was then constructed by free radical chemistry. 

The greater part of this chapter is concerned with the Diels-Alder and hetero-Diels-Alder reaction. The asymmetric version of both of these reactions can be catalysed with metal-based Lewis acids and also organocatalysts. The catalytic asymmetric 1,3-dipolar cycloaddition of nitrones and azomethine ylides is also discussed. Again, most success in this area has been achieved using metal-based Lewis acids and the use of organocatalysts is begiiming to be explored. This chapter concludes with a brief account of recent research into the asymmetric [2+2]-cycloaddition, catalysed by enantiomerically pure Lewis acids and amine bases, and also the Pauson-Khand [2- -2- -l] cycloaddition mediated by titanium, rhodium and iridium complexes. 

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