Indium-Triflate-Catalyzed Ritter Reaction in Liquid Sulfur Dioxide

The use of liquid sulfur dioxide as a reaction solvent facilitates the Ritter reaction between alcohols and nitriles. In(OTf)3 was found to be a viable catalyst for this transformation. The newly developed catalytic conditions for the Ritter reaction were successfully applied to the synthesis of various amides, which were formed in good to excellent yields. The catalytic activation of secondary alcohols for Ritter reactions in liquid sulfur dioxide was also found to be effective. Liquid sulfur dioxide can be used as a solvent for reactions involving carbenium ion intermediates. New catalytic conditions for the Ritter reaction are reported. Even unactivated secondary alcohols like cyclohexanol and cyclopentanol give good yields of the expected Ritter products when treated with nitriles in the presence of catalytic amounts of indium triflate in liquid sulfur dioxide.