SYNTHESIS AND REACTIVITY OF CROSS-CONJUGATED POLYENONES WITH A PLANARCHIRALITY

The complexes 6 are the first examples of a novel class of cross conju gated polyenones bearing a planar chirality introduced by an organomet allic moiety. Their synthesis is described using, as a key intermediat e, the easily accessible new phosphorane 9. The free double bond of th e selectively protected polyenes 6 reacts efficiently, although with l ow diastereoselectivities, in Diels-Alder or 1,3 dipolar cycloaddition reactions or with nucleophiles. Cyclopentyl radical also adds to 6, a nd this is the first example of a radical reaction in the presence of carbonyliron complexes. Decomplexation of the various adducts leads, i n good yields, to the corresponding polyfunctionalized free dienes, wh ich can be of further synthetic use.