Cyclisations carbonyl-alkyne

Molander recognised the potential of the Sml2-mediated Barbier addition to esters for the initiation of sequential processes (Chapter 5, Section 5.4). Two types of cascade have been developed that involve nucleophilic acyl substitution the first type involves double intramolecular Barbier addition to an ester group (anionic-anionic sequences),17 and the second type consists of a Barbier addition to an ester followed by a carbonyl-alkene/alkyne cyclisation of the resultant ketone (anionic-radical sequences) (Scheme 6.12).18,19... 

The reaction was first reported by Khand and Pauson et al. in 1973d It is the dicobalt octacarbonyl [Co2(CO)8l mediated or promoted one-step synthesis of a,p-unsaturated cyclopentenone from the [2+2+1] cycloaddition of alkyne, alkene and carbon monoxide, through an intermediate of alkynedicobalt hexacarbonyl complex. Therefore, this reaction is generally known as the Pauson-Khand reaction, Pauson-Khand cyclization, or Pauson-Khand cycloaddition. Occasionally, this reaction is also referred to as the Pauson-Khand annulation, Pauson-Khand multicomponent cycloaddition, Pauson-Khand carbonylative cocyclization, Pauson-Khand bicyclization, Khand annulation, Khand cycloaddition, Khand cyclization (cyclisation ), or Khand reaction.Among these names, the Pauson-Khand reaction is the one used most often. 

The product selectivity in the reaction of methylene cyclopropanes with alkynes is strongly substituent-dependent the reaction is catalysed by Ni(0)/tris(o-tolyl Iphosphite (eqn.47). The intramolecular hydroacylation of 4-pentenal is catalysed by low valent Co/PPh3 complexes and produces mainly cyclopentanone.Cyclopentenones and cyclohexenones are the products of the intramolecular carbonylation of vinyl iodides (eqn.48). A large variety of heterocycles are accessible the intramolecular Pd catalysed cyclisation of unsaturated a-haloamides. Treatment with base and PdfOAclj/PPhj converts 2,6-dibromo-l,6-dienes into cyclopentanes with exocyclic double... 

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