Arylation diarylmethanes

FIGURE 6. Diarylmethanes containing hetaryl groups synthesized by Pd-catalyzed aryl-benzyl or benzyl-aryl couphng... 

In these transformations, water is the only by-produced, so this arylation method is a state-of-the-art green route to diarylmethanes via Friedel-Crafts chemistry. 

Negishi, E., King, A. O., Okukado, N. Selective carbon-carbon bond formation via transition metal catalysis. 3. A highly selective synthesis of unsymmetrical biaryls and diarylmethanes by the nickel- or palladium-catalyzed reaction of aryl- and benzylzinc derivatives with aryl halides. J. Org. Chem. 1977,42, 1821-1823. 

Biaryls and diarylmethanes. These compounds can be prepared from coupling reactions of aryl iodides with organozinc reagents. Notably biphenylnonaflates are obtained from iodophenyl nonaflates at room temperature and they undergo further coupling at 55-60°. 

Another unexpected hydrogenolysis reaction was discovered by Lautens while attempting to expand the scope of the cvf/to-alkylation/dircct arylation of thiophenes. When benzyl chlorides were used as alkylating agents, significant amounts of the orffto-benzylation/hydrogenolysis product were obtained. An optimization of the reaction conditions led to an efficient synthesis of diarylmethanes (Scheme 41) [92], This reaction is unique compared to the aforementioned... 

Diarylmethanes. With (Ph3P>4Pd as catalyst, unsymmetrical ArCH2Ar are obtained from a cross-coupling reaction between aryl triflates and Bu4N[Bn,SnF2] in DMF. 

Unsymmetrical biaryh and diarylmethanes. Negishi et al have used a nickel-(0) complex or a palladium(0) complex as catalyst for the cross-coupling of aryl-or benzylzinc halides with aryl halides at room temperature to form biaryls or diarylmethanes. The zinc derivatives are prepared by reaction of aryl- or benzyl-lithium with zinc chloride or bromide. 

ArPb(OzC-CF3)2 Ar+ + Pb(02C CF3)2]. The aryl cations have been trapped with aromatic compounds to give biaryls [with certain substrates, notably poly-methylbenzenes, high yields (up to 88 %) are obtained], but with reactive aromatic substrates aryl cations are not the precursors to the biaryls and in these cases it is proposed that reaction proceeds via preliminary complex formation between the substrate and a species which contains an aryl-lead bond. Oxidative coupling of methyl-substituted benzenes by the reagent Pb(0Ac)4-CFs C02H to give biaryls and diarylmethane is also considered to involve formation of a radical cation in the primary step. A study has also been made of the plumbylation of monohalogeno-benzenes with Pb(OAc)4-CF3 COsH. ... 

A reaction to couple diarylmethanes 72 with aryl chlorides 73 was developed based upon the Pd(OAc)2/NiXantphos manifold which has unique reactivity that takes advantage of NiXantphos as a deprotonatable chelating aryldiphosphine ligand. In an isolated example, 72 was coupled with 73 in... 

In the case of benzylzinc chlorides prepared from benzylic chlorides by LiCl-promoted insertion of zinc, cross-coupling with aryl and aminoheteroaryl chlorides occurs smoothly in a mixture of THF and NMP with a catalytic system formed from Ni(acac)2 and PPhj (Scheme 4.89) [282]. Illustratively, the diarylmethane 388 is obtained in 90% yield after Ih at 60 °C. Similar reaction conditions are also efficient using aromatic bromides and tosylates as electrophilic partners. 

Specifically, diphenylmethane was prepared in >90% yield by the reaction of either Ph4Sn or Ph3SnMe with BrCH2Ph in the presence of PhCH2Pd(PPh3)2Cl.f The synthesis of polychlorinated diarylmethanes shown in Scheme 26 is noteworthy despite the modest product yields.f Most of the other currently known examples of Pd-catalyzed aryl-benzyl coupling pertain to the synthesis of heteroarenes (Scheme 27). 

---