Building Heterocyclic Systems with RC(OR)2+ Carbocations in Recyclable Bronsted Acidic Ionic Liquids: Facile Synthesis of 1-Substituted 1H-1,2,3,4-Tetrazoles, Benzazoles and Other Ring Systems with CH(OEt)3 and EtC(OEt)3 in [EtNH3][NO3] and [PMIM(SO3H)][OTf]

1-Aryl/alkyl-1H-1,2,3,4-tetrazoles can conveniently be synthesized in one-pot reactions from the corresponding amines by reaction with TMSN3 and CH(OEt)(3) using the readily available, recyclable, Bronsted acidic ionic liquids [EtNH3][ NO3] IL-1 and [PMIM(SO3 H)][OTf] IL-2 under mild conditions in high yields. Based on comparative reactions, whereas both ILs are excellent promoters, reactions are completed with shorter reaction times and in higher yields with IL-2. Among 24 examples provided, identical products were obtained via the two ILs, except in the case of 2-aminobenzoic acid where tetrazole was formed with IL-2 and 2-ethylquinazolin-4(3H)-one was formed with IL-1. By leaving out TMSN3 from the reaction, the in-situ formed CH(OEt)(2)(+) and EtC(OEt)(2)(+) (via their corresponding orthoesters) react under sonication with o-phenylenediamine bearing various substituents, o-aminothiophenol and o-aminophenol to form a wide array of benzazoles (benzimidazole, benzothiazole and benzoxazole) and quinazolin-4(3H)-one in high yields (18 examples). The two ILs reacted differently in reaction with 2-aminobenzamide, whereas quinazolin-4(3H) one was formed with IL-2/CH(OEt)(3), the unexpected N-ethylquinazolin-4(3H) one was isolated with IL-1/CH(OEt)(3). The latter was also formed from 2-aminobenzoic acid in IL-1/CH(OEt)(3). Mechanistic implications are addressed. The reported protocols enable rapid assembly of a host of heterocyclic systems in high yields with the added advantage of recycling and reuse of the ILs.