Triazolopyridines. Part 6. Ring opening reactions of triazolopyridines

Abstract

The triazole ring in 1,2,3-triazolo[l,5-a] -pyridinesand -quinolines, and in 1,2,3-triazoIo[5,1 -a3 isoquinolines can be opened with loss of nitrogen. The reagents described are bromine, aqueous sulphuric acid, glacial acetic acid, and selenium dioxide; the products from the triazolopyridines are dibromomethyl, hydroxymethyl, acetoxymethyl, and acyl derivatives of pyridine. The generality of the reactions is discussed. The first reported reaction in which the six-membered ring of a 1,2,3-triazolo[l,5-a]pyridine is opened, by hydride reduction, gives a triazolyl butadiene.We have reported in previous parts of this series that the triazolopyridine (la), triazoloquinolines (2) and (3), and triazoloisoquinoline (4) undergo directed lithiation which can lead to regiospecific substitution on the six membered rings. When this type of substitution can be combined with a good procedure for opening the triazole ring, with loss of nitrogen, we have syntheses of 2,6-disubstituted p y r i d i n e ~, ' ~ of 2,3disubstituted q u i n o l i n e ~, ' ~~ and of 1,3-disubstituted isoquinolines.' Most of our syntheses have involved the use of bromine for the ring opening, giving for example 2-dibromomethylpyridine (6a) which was easily converted into pyridine-2carbaldehyde,6 but restrictions with this reaction led us to study other ring opening procedures. This study has much widened -2

Triazolopyridines. Part 30. Hydrogen transfer reactions; pyridylcarbene formation

“…However, when we heated them in a water/ethanol mixture, the triazolopyridine 4b afforded 2-pyridylmethanol (67%). 32 The other triazolopyridines gave no reaction. These results show the thermal stability of compounds 4 in the conditions of solvents and temperatures studied, and the necessity of metal catalysis to obtain compounds 6.…”

TBAB‐Catalyzed Csp3–N Bond Formation by Coupling Pyridotriazoles with Anilines: A New Route to (2‐Pyridyl)alkylamines

“…[26] No cyclopropane product (2-(1-methyl-2-(p-tolyl)cyclopropyl)pyridine) was detected when styrene was added into the reaction in the presence or absence of aniline, indicating that no carbene intermediate was generated during the course of the reaction (Scheme 4d-e). The electrophilic carbon bearing the diazo was then attacked by the nucleophilic bromine [27] of the TBAB forming the benzyl bromide intermediate C and lead to the N 2 release and formation of tetrabutylammonium hydroxide (TBAH). The electrophilic carbon bearing the diazo was then attacked by the nucleophilic bromine [27] of the TBAB forming the benzyl bromide intermediate C and lead to the N 2 release and formation of tetrabutylammonium hydroxide (TBAH).…”

Triazolopyridines 22.1 Description of new 7,9-di(2-pyridyl)[1,2,3]triazolo[5',1':6,1]pyrido[3,2-d]pyrimidines

“…7 The other one was unexpected, and it was shown by HRMS to have formula C 18 H 13 N 5 . A study of their 1 H and 13 C NMR spectra shows the presence of two different 2-substituted pyridines.…”