Building Heterocyclic Systems with RC(OR)2+ Carbocations in Recyclable Brønsted 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]

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Abstract
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, Brønsted 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 TMS‐N3 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 re‐use of the ILs.

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