Fp Complexes of Alkenes

Much better known, and more widely applicable are the complexes developed over many years by Rosenblum Fp alkenes.The Fp group is CpFe(CO)2. These are complexes of alkenes with the cyclopentadienyldicar-bonyliron moiety and carry a positive charge. They have been found to be much more stable than the simple 

Although they are drawn as alkenes, the Fp complexes no longer show typical alkene reactivity, being inert to reactions such as catalytic hydrogenation and electrophilic attack. Instead they are susceptible to 

Some remarkable examples of stereocontrol have been reported using the Fp complexes of enediol ethers. 

2- diethoxyethene reacted with dimethyl copper lithium stereospecifically to give the syn adduct 6330. Acid treatment gave the trans complex 6331 with net inversion of the alkene geometry. Addition of the enolate of cyclohexanone, followed by acidification and decomplexation then gave the vinylated ketone 6334, with the cis alkene, the result of a second inversion. 

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