Approaches to phorbol and guanacastepene

Dicobalt hexacarbonyl alkyne complexes have been used in organic syntheses to generate complex organic molecules, with the aim of synthesizing phorbol and guanacastepene. In our approaches to both phorbol and guanacastepene we used combinations of three properties of dicobalt hexacarbonyl complexes. The ability of the dicobalt hexacarbonyl complex to stabilise propargylic cations, known as Nicholas carbocations, and the ability of these cations to form carbon-carbon bonds, known as the Nicholas reaction. The formal [2+2+1] cyclization that dicobalt hexacarbonyl complexes undergo when reacted with alkenes, to form cyclopentenones known as the Pauson–Khand reaction. The change in geometry of the alkyne that occurs when the alkyne forms a complex with dicobalt octacarbonyl, form linear to possessing carbon-carbon bond angles of 140° allowing the formation of cycloheptyne dicobalt hexacarbonyl complexes. [Continues.]