Tertiary cyclic amides in Vilsmeier type reaction with indoles

Abstract

Vilsmeier-Haack reaction also called Vilsmeier reaction was first used for the formylation of an active arene, during which a mixture of phosphorus oxychloride and dimethylformamide (Vilsmeier reagent) was added to N,N-dimethyl aniline [1].The reaction of indole with the Vilsmeier reagent, followed by base, is the classic and very efficient method for the 3-formylation of indoles (Scheme 1) [2]. Before the alkaline hydrolysis step, the product which was a salt, 3-[(dimethylamino)methylene]-3Hindolium chloride (1), was followed by a basic workup affording dimethylamine and aldehyde. 3-Acylindoles can be obtained from Vilsmeier reaction of indole and tertiary amides in combination to phosphorus oxychloride [3]. Scheme 1.The reaction of indole with Vilsmeier reagent for the 3-formylation of indoles

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“…Approximately, 70 % of all the dyes used in industry are azo dyes [4,5]. These compounds are characterized by the functional group (-N=N-) uniting two symmetrical and/or asymmetrical identical or non-azo alkyl or aryl radicals [6]. Most azo dyes are synthesized by diazotization of an aromatic primary amine, followed by coupling with one or more electron-rich nucleophiles such as amino and hydroxy [7].…”

Formation of indole trimers in Vilsmeier type reactions

“…The reactions of indole with the complex formed from different tertiary cyclic amides and phosphorus oxychloride were studied in our group. [19][20][21][22][23][24] In similar reactions of five-membered tertiary amide rings, 3-(1-alkyl-pyrrolidin-2-ylidene)-3H-indoles or ring opening products were obtained. The 3-(2-pyrrolidinylidene)-3H-indoles are stable compounds and they resist hydrolysis to the corresponding amino ketones.…”