Highly Chemoselective Heterogeneous Pd-Catalyzed Biaryl Synthesis from Haloarenes:  Reaction in an Oil-in-Water Microemulsion

Heterogeneous Pd/C-catalyzed reductive coupling of substituted haloarenes to the respective biaryls is effected with very high chemoselectivity in an oil-in-water microemulsion, using a reducing agent such as formate and a base, NaOH, in the presence of a catalytic amount of tetrabutylammonium bromide (TBAB) at 75 °C. Almost 100% biphenyl selectivity is obtained with iodobenzene. High coupling yields are achieved with 4-chlorotoluene and 4-chlorobenzaldehyde as the substrate. The competitive reduction reaction becomes predominant when the water-in-oil microemulsion is used as the solvent medium.