5- -2-cyclopentenone 1 -amino-1 -alkene

Their retro synthetic study was based around the Pauson-Khand cyclization (6), which couples an alkene, an alkyne, and a carbon monoxide source (typically dicobalt octacarbonyl) to give a cyclopentenone ring (Fig. 3.5, top). This reaction has been widely used for synthetic purposes, and some excellent reviews (7,8) have covered its principal features and the recent improvements to its experimental conditions. This reaction, in its intramolecular version, is ideal for the assembly of the l//-[2]pyrindi-none scaffold in two distinct versions, differing in the stereochemistry of the ring junction (Fig. 3.5, bottom). Hence, the readily available unsaturated amino acid derivatives 3.1a,b undergo intramolecular Pauson-Khand reaction to produce the two unsamrated scaffolds 3.2a,b. 

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