Palladium desymmetrized catalysts

The groups of Sigman and Stoltz have concurrently published the palladium-catalyzed oxidative kinetic resolution of secondary alcohols using molecular oxygen as the stoichiometric oxidant. Both communications also described a single example of a diol desymmetrization using a palladium catalyst in the presence of (—(-sparteine [Eqs. (10.42) ° and (10.43) ] ... 

The peptide-based phosphine ligand 105 was identified from a polymer-supported phosphine library of 75 members [154]. Enantioposition-selective desymmetrization of the meso-cyclopentenediol derivative 100 was promoted by a palladium complex of 105 to afford the cyclic carbamate 101 with 76% ee. This result demonstrated that the combinatorial approach is effective in the lead-generation stage of stereoselective catalyst development [155, 156]. The resin-supported palladium complex of Ac-D-Phg-Pro-D-Val-Pps-D-Leu-NH resin 106, which has also been developed through the combinatorial approach. 

Quite recently, another Pd-catalyzed enantioselective desymmetrization has been also reported by Erase, which constitutes the ejco-methylenecycloalkanes containing the quar-temary carbon center.t In this report, treatment of the bisnonaflate 155 with acrylate in the presence of BINAP and palladium catalyst gave the tetraene 156 in 37% yield and in up to 28% enantiomeric excess (Scheme 38). 

Oxygen nucleophiles have not frequently been used as terminators in cascade car-bometallation reactions. The intramolecular carbopalladation starting with an iodo- or trifluoromethylsulfonyloxyalkenyl-substituted derivative in the presence of tetrabutylam-monium acetate led to a suitable precursor of the sesquiterpene (-)-A (i )-capneUene. In this case, desymmetrization of the prochiral precursor was achieved using (5)-BINAP as the ligand on the palladium catalyst (Scheme 32). ... 

Enantioselective C—H activation/C C cross-couplings using chiral palladium catalysts, and boronic acids was recently reported. In a remarkable study, Yu and coworkers demonstrated the desymmetrization of prochiral C—H bonds on geminal aryl or methyl groups with monop-rotected amino acids as a source of chirality and pyridine as the directing group.Benzoquinone promoted both the... 

Lautens has spearheaded the study of a range of metal-catalyzed methods for the desymmetrization of various meso-oxabicyclooctanes [40]. In initial work, enantioselective nickel-catalyzed hydroalumination reactions of substrates such as 148 proved effective for the generation of cycloheptene 150 (95% ee, Scheme 14.24) [118], as also described in Section 7.5. The related desymmetrization reactions could be effected with carbon nucleophiles as well [119, 120], Thus, asymmetric ring-opening of 145 with Me2Zn mediated by a palladium catalyst prepared in situ with ligand 146 [121] led to the C3-C9 fragment (147) of the polyether antibiotic ionomycin (151) [120]. 

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