Reductive Formylation of Aromatic Halides under Low Carbon Monoxide Pressure Catalyzed by Transition-Metal Compounds

Substituted aryl halides were formylated under 50 psi pressure of carbon monoxide in the presence of a hydrogen donor such as poly(methylhydrosiloxane) (PMHS) and a homogeneous transition-metal catalyst to give aromatic aldehydes in good yields. Addition of an amine was necessary to trap the hydrogen halide formed. Sodium formate could serve as a hydrogen donor in the absence of a base. Conditions for selective formylation of one position in dihalobenzenes such as iodobromobenzenes and bromochlorobenzenes were developed. Various transition-metal catalysts were examined, of which palladium compounds were found to be most efficient.