Haloarenes biaryl synthesis

The protocol offers a direct and efficient method for the synthesis of the boronic ester in the solid phase, which hitherto met with little success using classical methodology (Scheme 1-42). A solid-phase boronate (113 [155], 114 [156]) is quantitatively obtained by treating a polymer-bound iodoarene with the diboron (82). The subsequent coupling with haloarenes furnishes various biaryls. The robot synthesis or the parallel synthesis on the surface of resin is the topic of further accounts of the research. 

Watanabe, T. Miyaura, N. Suzuki, A. Synthesis of sterically hindered biaryls via the Pd-cat-alyzed cross-coupling reaction of arylboronic acids or their esters with haloarenes. Synlett 1992, 207-210. 

The mixed Ullman reaction in which two haloarenes couple in the presence of copper powder is still commonplace in industrial process, but the catalyzed cross-coupling reactions appear to be more productive and provide reliable results in synthesis of unsymmetrical biaryls (Scheme 30). The isomeric michel-... 

Previously Davidson and Triggs have reported that arylboronic acids react with sodium palladate to give the dimeric biaryls. The synthetic utility of this dimerization reaction is, however, limited owing to stoichiometric requirement of the palladium compound. On the other hand, the palladium-catalyzed crosscoupling reaction between arylboronic acids and haloarenes in the presence of bases provides a clean synthesis of biaryls (Eq. 106) In this case, sodium carbonate has been proven to be most effective base. 

Reaction of Arylboronic Acids with Haloarenes Synthesis of Sterically Hindered Biaryls [110] (Scheme 2-66)... 

The nickel-catalyzed reductive homocoupling of haloarenes is an excellent method for the synthesis of symmetrical biaryls (Eq. 22). The remarkable ability of [Ni(cod)2] to promote the stoichiometric formation of biaryls from aryl iodides and bromides was originally reported by Semmelhack, Helquist, and Jones [25a]. Unlike the Ullmann reaction [3], the Ni-promoted homocoupling of... 

In 1901, Fritz Ulknann (Figure 1.6) showed that stoichiometric amounts of copper enabled the reductive coupling of haloarenes for the synthesis of symmetrically substituted biaryls (Scheme 1.3) [27]. 

In another publication, the Miyaura group described the cross-coupling of aryl triflates to arylboronic esters as well as the synthesis of unsymmetrical biaryls using a modified protocol. In both cases, the authors used KOAc as base since stronger bases such as K2CO3 afforded symmetrical biaryls (see also 4.18) as by-products. The proposed mechanism of this reaction is depicted in Scheme 5-166. Oxidative addition of the catalyst to haloarene followed by displacement of the halide leads to the corresponding pentacoordinated palladium(II) species. Transmetalation with bis(pinacolato)diboron followed by reductive elimination yields the arylboronic ester. 

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