Ethers, vinyl Pauson-Khand reaction

Cyclopropene can also be used as the aUcene component and affords bicyclo[3.1.0]hexen-2-ones upon reaction with alkyne dicobalt octacarbonyl complexes in the presence of NMO (Scheme 250). Vinyl ethers and vinyl esters serve as ethene equivalents in Pauson-Khand reactions. For example, reaction of vinyl benzoate with complex (169) furnished cyclopentenone (170) (Scheme 251). This reaction was used in a synthesis of (-l-)-taylorine and nortaylorine. Allenes participate in intermolecular Pauson-Khand reactions affording alkylidene-substituted cyclopentenones (Scheme 252). ... 

Production of the tetrasubstituted cyclopentenone (15a, 15b)) involves condensing the protected vinyl ether (16) with (12) via a Pauson-Khand reaction. Studies on the Pauson-Khand reaction , 1 have shown that upon condensing an unsymmetrical alkene with an unsymmetrical alkyne in the presence of a cohalt carbonyl compound give rise to mixtures of diastereomers (Fig 1) with the bulkier substituents of the alkene and alkyne being a to the carbonyl of the cyclopentenone. However, the stereochemistry a to the... 

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