Studies on the Development of the Tritylsulfenyl Group as a Nitrogen Protecting Group and Application in a Synthesis of δ-Coniceine

The (triphenylmethyl)sulfenyl (tritylsulfenyl, TRS) group was found to possess properties which should make it useful as a nitrogen protecting group. The almost instantaneous reaction of TrSCl (6) with amines produced the corresponding triphenylmethanesulfenamides. The TRS group was found to render the nitrogen atom nonbasic and relatively nonnucleophilic, was stable to aqueous acid, aqueous base, and various reducing agents, and was moderately stable to Moffat oxidation conditions. The TRS group could be cleaved under mild conditions, generating the amine with either CuCl2/EtOH-THF, HI/THF-H20, or trimethylsilyl iodide (Me3SiI)/CH2Cl2. A synthesis of δ-coniceine (16) illustrates carbon-carbon bond formation with tritylsulfenimine methodology and the utility of the tritylsulfenyl group as a nitrogen protecting group.