Unusual reactions in molecules with crowded functional groups: sulfonamide reduction under oxidizing conditions in camphor derivatives

Abstract

The reaction of the camphor-derived dialkyne 1 with polarizable compounds like acids and halogens leads to the formation of cationic species of the type 2 with a pentacyclic structure. These are stable in trifluoroacetic acid, but undergo reduction of the sulfonamide to a sulfinamide group in other solvents. The reaction mechanism was studied by NMR measurements. With iodine as reagent, further reactions occur due to the low stability of the carbon–iodine bonds, leading to the introduction of a carbonyl group into the newly formed carbocyclic ring. The crystal structure of the acetate derivative 8 shows that the reduction of the sulfonamide group occurs stereoselectively, leading to the S-configuration of the sulfur atom in the sulfinamide. This configuration can be inverted by strong acids. In addition, reduction of the sulfinamides to a sulfenamide was observed in the reaction mixture with iodine.