Oxidative desulfurization of azole-2-thiones with benzoyl peroxide
Wolfe, Derek Michael
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1-Alkyl-3-methylimidazole-2-thiones were prepared in one pot and subsequently converted to 1-alkyl-3-methylimidazolium benzoates through a sequence consisting of an oxidative desulfurization with benzoyl peroxide and a novel anion exchange. Also reported are the outcomes of exchanges with other anions, acidifications of the imidazolium benzoates to other salts, and the syntheses of both 1,3-diphenylimidazolium and 3-alkylthiazolium salts from the corresponding azole-2-thiones. This oxidative desulfurization was also appropriate for the synthesis of neutral imidazoles from 1-alkylimidazole-2-thiones, which were prepared from amino acids by way of 2-thiohydantoins. Four such sequences are described, one of which constitutes a formal synthesis of three imidazole alkaloids from the sponge Leucetta. The merits of these routes in terms of both adaptability and operational simplicity are emphasized. A chiral imidazolium salt featuring camphor was pursued, but an imidazole-2-thione precursor suited to desulfurization could not be prepared; the desired salt could not be assembled with conventional methods, either. The unsuitability of some imidazolium ionic liquids in an adaptation of the phase transfer catalyzed halogenation is discussed in the context of ³-adamantane amino acids.