Cyclopentadiene, derivatives introduction

In 1990, Choudary [139] reported that titanium-pillared montmorillonites modified with tartrates are very selective solid catalysts for the Sharpless epoxidation, as well as for the oxidation of aromatic sulfides [140], Unfortunately, this research has not been reproduced by other authors. Therefore, a more classical strategy to modify different metal oxides with histidine was used by Moriguchi et al. [141], The catalyst showed a modest e.s. for the solvolysis of activated amino acid esters. Starting from these discoveries, Morihara et al. [142] created in 1993 the so-called molecular footprints on the surface of an Al-doped silica gel using an amino acid derivative as chiral template molecule. After removal of the template, the catalyst showed low but significant e.s. for the hydrolysis of a structurally related anhydride. On the same fines, Cativiela and coworkers [143] treated silica or alumina with diethylaluminum chloride and menthol. The resulting modified material catalyzed Diels-Alder reaction between cyclopentadiene and methacrolein with modest e.s. (30% e.e.). As mentioned in the Introduction, all these catalysts are not yet practically important but rather they demonstrate that amorphous metal oxides can be modified successfully. 

Ligand-substitution reactions (or nucleophilic attack at the metal) in cyclopentadienyl complexes of palladium have been used to prepare new derivatives. The classical introduction of a cyclopentadienyl moiety by use of TlCp or NaCp and a cationic or halo palladium complex has been employed in the synthesis of complexes [Pd( 7 -Cp)(dppe)]Tf " and PdCp 3-(CHO)C6H3C(H)=NCy. A novel route has been applied that involves deprotonation of cyclopentadiene by a coordinated hydroxyl group to afford the cyclopentadienyl complexes shown in Equation (63). ... 

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