Synthesis of Aromatic Aldehydes by CH Formylation of Aromatics with Silyl Formates Prepared from CO ₂ and Hydrosilanes

Despite the recent remarkable progress in CO 2 fixation reactions, the methods for the synthesis of aldehydes from CO 2 are quite limited partly because of the lability of the resulting formyl group and difficulty in the controlled deoxygenative CO 2 conversions leading to CH and CC bond formation. Here, we have developed the direct CH formylation of electron‐rich aromatics using silyl formates, prepared from CO 2 and hydrosilanes, in the presence of BCl 3 or BBr 3 . This is the first report on the direct CH formylation of aromatics with silyl formates. Useful compounds including a biologically active compound and octaethylporphyrin were synthesized by fixing one to four CO 2 molecules in a stepwise manner. DFT calculations have been done to elucidate the reaction mechanism including a dual role of BBr 3 in the activation of silyl formate, HCO 2 SiMe 2 Ph, and electrophilic aromatic substitution.