Efficient hydroxymethylation reactions of iodoarenes using CO and 1,3-dimethylimidazol-2-ylidene borane.

A hydroxymethylation reaction of a variety of iodoarenes proceeded effectively in the presence of CO, NHC-borane, diMeImd-BH3 (2) as a radical mediator, and a catalytic amount of AIBN. The reaction took place chemoselectively at the aryl-iodine bond but not at the aryl-bromine and aryl-chlorine bonds. A three-component coupling reaction comprising aryl iodides, CO, and electron-deficient alkenes also proceeded well to give unsymmetrical ketones in good yields. Control experiments show that 2 would act as a hydrogen donor to acyl radicals and iodinated NHC-borane as a reducing agent of aldehydes.