DPEphos

Bidentate ligands with very wide bite angles (like dpephos or xantphos, Scheme 4) are likely to form unstable chelates prone to dechelation at elevated temperatures, thus giving another route to monophosphine species. The application of such ligands to the crosscoupling of sterically hindered bromides and arylboronic acids under strictly anhydrous conditions enforced by the addition of molecular sieves has been shown to be advantageous (118).398... 

Amides and sulfonamides undergo intramolecular chemistry to form aryl amides and aryl sulfonamides (Equations (17)—(19)) in the presence of palladium catalysts ligated by arylphos-phines.35,89 Initially, complexes of P(furyl)3 and P(o-tol)3 were most effective catalysts, but complexes of Hayashi s MOP and van Leeuwen s DPEphos and xantphos have lately been shown to be more active.90 In the presence of catalysts containing one of these ligand systems, five-, six-, and seven-membered rings were formed from halogenated benzamides or from substrates containing an acetamide, an A-carbobenzyloxy, or a t-butylcarbamate substituent tethered to the aryl halide (Equations (18) and (19)) ... 

Several palladium catalysts for formation of aryl sulfides from aryl halides have been investigated more recently. A combination of Pd2(dba)3 and DPEphos catalyzed the formation of a broad range of diaryl sulfides in the presence of 1 mol.% palladium and NaO-t-Bu base in toluene solvent.12,rThe highest yields of alkyl aryl sulfides were obtained from aryl triflates and n-butyl thiol catalyzed by a combination of palladium acetate and BINAP. However, these reactions contained 10 mol.% catalyst, were long, and required deactivated aryl triflates. A combination of Pd2(dba)3 and DPPF catalyzed the coupling of thiols with resin-bound aryl halides.121... 

Chloroprene (2-chloro-l,3-butadiene 105), which is a mass-produced, inexpensive industrial material, is an excellent precursor to a variety of terminal allenes 107 [97]. The palladium-catalyzed reaction of 105 with pronucleophiles 106 in the presence of an appropriate base gave the terminal allenes 107 in good yields (Scheme 3.53). The palladium species generated from Pd2(dba)3-CHC13 and DPEphos was a good catalyst for these reactions of chloroprene. In contrast, (Z)-l-Phenyl-2-chloro-l,3-buta-diene, which is isostructural with the bromo-substrate 101, was nearly inert under these conditions. There is no substituent at the vicinal ris-position to the chloride in 105, which allows oxidative addition of the C-Cl bond in 105 to the Pd(0) species. 

SCHEME 25. High turnover numbers observed in the Pd-catalyzed cross-coupling with Pd(dppf)a2 or Pd(DPEphos)Cl2 as a catalyst... 

A systematic investigation of the frans-selective monosubstitution of a variety of 1,1-dibromo-1-alkenes has established that their reaction with alkenyl-87, alkynyl-85 and arylzincs86 in the presence of 1-5 mol% Pd(DPEphos)Cl2 provides a generally applicable and satisfactory procedure (Scheme 37). For most cases, THF is a reasonably satisfactory... 

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