New access to 1,3-dialkyl-2,3-dihydro-2-imino-1H-imidazoles and their application to the first total synthesis of naamine B, a marine 2,3-dihydro-2-imino-1,3-dimethyl-1H-imidazole alkaloid

1,3-Dialkyl-2,3-dihydro-2-imino-1H-imidazole derivatives are synthesized in 49-86% yield by treatment of 1,3-dialkyl-2-(phenylsulfanyl)imidazolium salts with primary carbamates or amides in the presence of a base such as LDA or NaH, and the first total synthesis of naamine B, a marine 2-imino-2,3-dimethyl-1,3-dihydro-1H- imidazole alkaloid, is achieved by application of this reaction as a key step.