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Triazenes by Acid-Mediated Opening of the Dihydro-1,2,3-triazole Ring of1,3-Dipolar Cycloadducts of Organic Azides to Cyclic Ketene N,N-Acetals

✍ Scribed by Helmut Quast; Manfred Ach; Dieter Regnat

Publisher: John Wiley and Sons
Year: 2005
Tongue: English
Weight: 194 KB
Volume: 2005
Category: Article
ISSN: 1434-193X
DOI: 10.1002/ejoc.200500366

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✦ Synopsis

Abstract

Spirocyclic 1,3‐dipolar cycloadducts 1 and 4 of azides to heterocyclic ketene N,N‐acetals open their dihydro‐1,2,3‐triazole ring in the presence of weak Brønsted acids to afford novel 1,3‐substituted triazenes 2X and 5X, respectively, which form colorless, crystallized tetrafluoroborates (X = BF~4~) and hexafluorophosphates (X = PF~6~). Ring‐opening is reversed in alkaline solutions. Methyl triflate methylates the dihydro‐1,2,3‐triazole ring of 1a and 4 at N‐3 and thus induces ring‐cleavage to 1,3,3‐trialkyltriazenes 3 and 6, respectively. The 1,3‐substituted triazenes 2aX, 2bBF~4~, 2dX and 5X exist as tautomers that have the larger substituents, which include the heterocyclic rings, connected with the azo group (N‐1). By contrast, triazene 2cPF6 has a bulky alkyl group at each terminal nitrogen and hence forms two rapidly equilibrating tautomers of similar stability. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

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