Building Heterocyclic Systems with RC(OR)₂⁺ Carbocations in Recyclable Brønsted Acidic Ionic Liquids: Facile Synthesis of 1‐Substituted 1<i>H</i>‐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]

Abstract

Abstract 1‐Aryl/alkyl‐1 H ‐1,2,3,4‐tetrazoles can conveniently be synthesized in one‐pot reactions from the corresponding amines by reaction with TMSN 3 and CH(OEt) 3 using the readily available, recyclable, Brønsted acidic ionic liquids [EtNH 3 ][NO 3 ] IL‐1 and [PMIM(SO 3 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(3 H )‐one was formed with IL‐1 . By leaving out TMS‐N 3 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(3 H )‐one in high yields (18 examples). The two ILs reacted differently in reaction with 2‐aminobenzamide, whereas quinazolin‐4(3 H )one was formed with IL‐2 /CH(OEt) 3 , the “unexpected” N ‐ethylquinazolin‐4(3 H )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.