Pd-mediated coupling reactions

Ley and Schanze [14, 68] have synthesized a series of PPE-type polymers that contain/ac-(5,5 -diethynyl-2,2 -bipyridine)Re(I)(CO)3Cl as part of the n-conju-gated main chain by a Pd-mediated coupling reaction, as illustrated in Scheme 9. The polymers differ with respect to the mole ratio of 4,4 -diethynylbiphenyl (59) and (5,5 -diethynyl-2,2 -bipyridine)Re(l)(00)301 (58) used in the polymerization reaction mixture. Four different polymers have been prepared and contain 0 (Po), 10 (Pio), 25 (P25), and 50 (P50) mol% of the Re(I) repeat units in the polymer chain, respectively (Scheme 9). 

Zhang, H.-C. Daves, G. D. Water facilitation of Pd-mediated coupling reactions. Organometallics 1993, 12,1499-1500. 

The Pd-mediated coupling involving organomercury and alkenes is useful for the synthesis of C-5 substituted 2 -deoxyribonucleosides[376]. The ethylur-idine 415 is prepared by the reaction of the 5-chloromercuriuridine 414 with... 

The key to the success of the synthesis was the development of a novel method for enantioselective formation of a-arylpyrrolidines. In this method, (-)-sparteine-mediated, enantioselective lithiation of N-Boc-pyrrolidine 19 was followed by an in situ transmetallation to zinc and Pd-catalyzed coupling reaction with aryl bromide 3, which afforded 2-arylpyrrolidine in 63% isolated yield and 92% ee. Notably, the acidic aniline NH2 group was tolerated under the coupling reaction conditions. 

Pd-mediated coupling of 50 could, in principle, terminate via p-elimination of either the C8 or C12 hydrogens. However, only the latter was observed. In our case, pentacycle 46 has only the C8 hydrogen available, and the normal course of the Heck reaction would be expected to produce pyridone 58 (Scheme 30). If p-elimination proved slow, an added hydride source might capture the palladium a-complex and provide the desired formal conjugate addition product 51. 

The scope and limitations of Pd(0)-mediated coupling reactions between aromatic halides linked to a polystyrene resin and boronic acid derivatives (Suzuki coupling) or arylstannanes (Stille coupling) have been reported. For all the reactions, the conditions were optimized and evaluated with various reagents. In most cases, products were obtained in excellent yields upon cleavage from the solid support (Eq. (63)) [101]. 

The coupling reaction of benzofuranylthioethers (28) and tri-/2-butylpyrazinylstannane was carried out in the presence of Pd2(dba)3-TFP and Cul diphenylphosphinate (CuDPP) as a unique mediator for these Pd-catalyzed coupling reactions [22]. A mild synthetic method for biheteroaryl ketone 29 was developed under neutral reaction conditions. 

Aldol reaction, oxidation (alcohol —> ketone), aromatie metalation (nBuLi), Pd(0)-mediated coupling reactions (Heck, Stille, Suzuki). 

Palladium catalysis has been found to promote the Ullman reaction, and may also influence the course of the reaction. Under typical Ullman conditions homo-coupling (349, 350) is favored in the reaction between 3-iodopyridine and bromo-nitrobenzenes, whereas the presence of Pd(PPh3)4 favors cross-coupling (348). Both 2- and 4-iodopyridines and 2-bromopyridine undergo Pd-mediated coupling (84JOC5237 93TL3421). 

Alternatively, the Hiinig s base mediated coupling reactions of aryl iodides have been effected in supercritical carbon dioxide (SCCO2) as the reaction medium with complexes of Pd(OAc)2 or Pd(Cp3COO)2 and tri(2-furyl)phosphine (PFU3) at 2 mol% catalyst loading to afford the respective biaryls in excellent yields [54]. 

---