Thermal Rearrangement of 1‐Substituted 5‐Azido‐4‐Cyano‐1H‐1,2,3‐Triazoles

h o l e s are five-membered ring heterocycles which may be considered as ring-closed forms of conjugated 1,9dipoles (Scheme l).' The equilibrium positions are usually shifted towards the aromatic compounds, except for a-diazoketones (or esters) and acyl azides (6 and 8, X = 0) of which the corresponding heterocycles are unknown.* a-Diazothioketones and thioacyl azides, on the contrary, only exist as transient intermediates which cyclize to thiadiazoles and thiatriazoles respectively (5 and 7, X = S).3 lminodiazomethanes and iminoazides (6 and 8, X = NR) most often cyclize to triazoles and tetrazoles (5 and 7, X = NR), but they can be stabilized in the open-chain form by introducing strong electron-withdrawing substituents at the imine n i t r~g e n .~

Molecular Rearrangements of 1h‐1,2,3‐Triazoles and 1,2,3‐Thiadiazoles

L'abbé

1990

Functionalized Chloroenamines in Aminocyclopropane Synthesis ‐ VII. A Diastereocomplementary Approach to Amino‐Bicyclo[n.1.0]Alkanenitriles on the Basis of Chlorinated Enamines

Vilsmaier

Stamm

Dauth

et al. 1992

Reductive dechlorination of amino-chlorobicycloalkanenitriles 5a-c was achieved by sodium in tert.butyl alkohol/THF to give the bicyclic nitriles 6a-c. LiAIH,, as dechlorination reagent caused a ring opening reaction with 5b,c producing diamines 7b,c. The bicyclic chloro compounds 5b,c could by obtained from enamines 1 via dichloroenamines 4. Monochlorination of 1 b,c and subsequent cyclopropanation with cyanide yielded endo-bicycloalkanenitriles 3b.c. Compounds 3 and 6 thus generally can be synthesized in a diastereocomplementary way starting from enamines 1.

Thermolysis of 4‐Heteroaryl Substituted 5‐AZIDO‐1H‐1,2,3‐Triazoles: Competition Between Rearrangement and Decomposition

L'abbé

Vercauteren

Dehaen

1994

5-Azidotriazoles bearing a thiazole, benzothiazole or pyridine ring at the 4-position were synthesized and thermolyzed at 60°C. Whereas the 5-azido-4-(thiazol-2-yl)triazole 4 decomposed with extrusion of nitrogen and formation of the triazene 5 as the sole reaction product, the 5-azido-4-(benzothiazol-2-yl)triazoles 1 la,b furnished mixtures of the triazenes 12a,b and the tetrazoles 14a,b. In the case of the 5-azido-4-(2-pyridyl)triazoles 17ad, the product distribution was found to depend strongly on the N-1 aryl substituent, favouring the tetrazole 20 by increasing the electron-withdrawing capacity of this group.