Fluorobissulfonylmethyl Iodides as Lewis Acid Catalysts

Significance

The Shibata group reports the use of fluorobissulfonylmethyl iodides as Lewis acid catalysts. The results of catalyst screenings suggest the importance of the iodine atom for catalysis, the Lewis acidity of which is further supported by both computational and experimental studies. The catalyst is active in the presence of weakly nucleophilic bases; however, nucleophilic ones, including halides, are not compatible, suggesting that the transformation proceeds by Lewis acid catalysis. The authors also use these halogen-bond catalysts for a transfer hydrogenation that was previously reported with other halogen-bond donors (A. Bruckman, M. A. Pena, C. Bolm Synlett 2008, 900; W. He, Y.-C. Ge, C.-H. Tan Org. Lett. 2014, 16, 3244).

Comment

Recently, halogen bonding has attracted a lot of attention in the context of catalysis because it can act as an alternative or complementary interaction to hydrogen bonding. The iodine atom shows Lewis acidity due to its attached electron-deficient backbones, typically perfluoroarenes or cationic hetarenes. Here, the authors installed an iodine atom on fluorobissulfonylmethyl groups. Despite the innovative design, the catalytic activity is moderate compared with conventional Lewis acid catalysts, presumably because of the inherent dilemma of stability and reactivity for halogen-bond donors. Namely, stronger halogen-bond donors are inherently better electrophilic iodination reagents, probably one of the major challenges for halogen bonding in catalysis.