The synthesis and unimolecular decomposition of four novel Δ¹-1,2,4-triazolines

Abstract

Treatment of 4-tert-butyl-3,3-dimethyl-5-methylene-Δ1-1,2,4-triazoline (3) with benzonitrile oxide (9), diphenylnitrile imine (10), phenyl azide, and p-nitrophenyl azide led, in each case, to 1,3-dipolar cycloaddition. The products, Δ1-1,2,4-tri-azolines that are spiro-fused to another 5-membered ring, could be isolated in pure form in three of the four cases. All four are thermally unstable and decompose by loss of N2 from the Δ1-1,2,4-triazoline moiety to form an azomethine ylide. Subsequent reactions of those ylides are described.

Thermal intramolecular reactions of Δ1-1,2,4-triazolines with extended exocyclic unsaturation

“…Such addition, followed by elimination of aniline and electrocyclic ring opening, constitutes formal anilide methanolysis (reaction [8] Although alternative mechanisms are conceivable, including initial C-N bond rupture as in Scheme 4 , they fall short on several counts. First, and most telling, is the fact that analogous triazolines d o not lose N2 under similar conditions (1,2), and that the thiadiazoline analogue (20) already mentioned above (11) decomposes with loss of N2 only at a much higher temperature. Second, formation of a dipolar intermediate (25) in the rate-deternlining step (Scheme 4) should be facilitated, not retarded, in a more polar solvent.…”

“…Methanol, Baker Analyzed, was used as received. The synthesis and spectra of 1 and 3 have been described (1,2).…”

Triazaspirocycles: Occurrence, Synthesis, and Applications

“…Construction of triazaspirocycles is also commonly carried out with azides. Numerous examples of azide-derived triazaspirocycles have been reported using methylene-substituted heterocycles (Schemes 10 and 11 ) [63-67]. Nitrile imines, formed from the corresponding hydrazonoyl chlorides, have also been implemented in the synthesis of triazaspirocycles (Scheme 12 ) [67-69].…”

“…Schwan et al observed degradation of this scaffold gave an azomethine ylide upon loss of nitrogen gas (Scheme 29 ) [67]. This ylide underwent a [1,4]-hydrogen shift to give the 1,2,3-triazoline, which reacted further to undergo heterolytic cleavage and enamine hydrolysis to give the 1,2,3-triazole and amidine.…”

Spirocyclic Orthoesters, Orthothioesters and Orthoaminals in the Synthesis and Structural Modification of Natural Products

“…An additional annular nitrogen is built into the skeleton when a triazole is one of the reactants. Diphenylnitrile imine, PhC≡N +-NPh (19), undergoes a 1,3-dipolar cycloaddition with 4-tert-butyl-3,3-dimethyl-5-methylene-1,2,4-triazoline (17) to afford the 1,2,4,6,7-pentaazaspiro- [4.4]nonane 20 (Scheme 6). 17 The adduct, upon thermolysis in benzene, affords pyrazole 21 (94%).…”