5-Aryl-4-iodoimidazoles

Bromo- and iodoimidazoles are useful intermediates for further functionalization. 4(5)-Aryl- I //-imidazoles 57 can be efficiently and selectively prepared by palladium-catalyzed Suzuki-Miyaura reaction of commercially available 4(5)-bromo-l//-imidazole 56 with arylboronic acids under phase-transfer conditions, which then underwent highly selective palladium-catalyzed and copper(I) iodide mediated direct C-2-arylation with a variety of aryl bromides and iodides under base-free and ligandless conditions to produce 2,4(5)-diaryl-l//-imidazoles 58 in modest to good yields <07JOC8543>. A new procedure for the synthesis of a series of substituted 2-phenylhistamines 60 utilizing a microwave-promoted Suzuki... 

Imidazole zinc reagent 372 was made from 2-iodoimidazole 371 with activated zinc dust. The organozinc reagent was cross-coupled with aryl iodides and alkenyl iodides, in good yields (Scheme 88), <1997T7237>. 

N-l-Substituted iodoimidazoles behave normally with arylboronic acids to give cross-coupled products <2005T6056>. N-l-Substituted-2-bromoimidazoles also coupled efficiently with aryl boronic acids and alkenyl boronic acids to give cross-coupled products in high yields (Scheme 95) <2004JOC8829>. 

The use of Bu3SnH and AIBN has become commonplace in the synthesis of annulated arenes by the intramolecular aromatic substitution via aryl and heteroaryl radicals (see Chapter 13). Nevertheless, a simpler and more environmentally friendly protocol should be the direct generation of the o-aryl or heteroaryl radicals by UV-induced homo lytic cleavage of an aryl halide with subsequent intramolecular attack onto an arene in proximity. Accordingly, tricyclic [2,1-a] fused heterocycles were regioselectively formed in high yields from N-(2-arylethyl)-2-iodoimidazoles upon irradiation in acetonitrile (Scheme 14.18) [92]. 

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