Rhodium‐Catalyzed Formylation of Unactivated Alkyl Chlorides to Aldehydes

The first rhodium‐catalyzed formylation of non‐activated alkyl chlorides with syn gas (H(2)/CO) allows to produce aldehydes in high yields (25 examples). A catalyst optimization study revealed Rh(acac)(CO)(2) in the presence of 1,3‐bisdiphenylphosphinopropane (DPPP) as the most active catalyst system for this transformation. Key for the success of the reaction is the addition of sodium iodide (NaI) to the reaction system, which leads to the formation of activated alkyl iodides as intermediates. Depending on the reaction conditions, either the linear or branched aldehydes can be preferentially obtained, which is explained by a different mechanism.