Pyrolysis of annelated hexa- and heptamethylene-tetrazoles: Formation of 9- and 10-membered cyclic carbodiimides

Wentrup, Curt; Vosswinkel, Michael

doi:10.1016/j.jaap.2015.11.013

Cited by 9 publications

(6 citation statements)

References 20 publications

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“…A cyanamide 364 was, however, isolated together with the ring-opened product 365 following FVP of the dibenzotetrazoloazocine 360 (Scheme ). It is likely that these products are formed by ring opening of either the nitrene 361 or the carbodiimide 362 to a diradical 363 (a type II ring opening; Scheme ) analogous to the reactions of the tetra- and pentamethylenetetrazoles described above and 2-pyridylnitrenes described in section …”

Section: Azidesmentioning

confidence: 97%

“…The reactions are assumed to proceed via ring opening of the cyclic imidoylnitrenes to diradicals followed by hydrogen shifts FVP of the annelated polymethylenetetrazoles 340 – 343 − yielded cyclic carbodiimides 344 – 347 (eqs –53), which are likely formed by rearrangement of intermediate imidoylnitrens in the same way that 1,5-disubstituted tetrazoles yield open-chain carbodiimides (cf. Scheme ).…”

Section: Azidesmentioning

confidence: 99%

“… The corresponding unsaturated azocine and azonine derivatives 348 and 354 afforded cyclization products 353 and 359 via the intermediate, observable carbodiimides 350 and 356 (Scheme ). There was spectroscopic evidence for the additional formation of the cyanamide 351 , but not 357 …”

Section: Azidesmentioning

confidence: 99%

“…291 The tetra-and pentamethylenetetrazoles underwent FVP to form the alkenylcyanamides initially, and these cyclized to Ncyanopyrrolidines by exo-trig addition of the cyanamide There was spectroscopic evidence for the additional formation of the cyanamide 351, but not 357. 297 A cyanamide 364 was, however, isolated together with the ring-opened product 365 following FVP of the dibenzotetrazoloazocine 360 (Scheme 48). 292 It is likely that these products are formed by ring opening of either the nitrene 361 or the carbodiimide 362 to a diradical 363 (a type II ring opening; Scheme 48) analogous to the reactions of the tetraand pentamethylenetetrazoles described above and 2-pyridylnitrenes described in section 4.7.…”

Section: Imidoyl Azides [Rc(nr′)−n 3 ] and Imidoylnitrenes [R(cnr′)−n]mentioning

confidence: 99%

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Flash Vacuum Pyrolysis of Azides, Triazoles, and Tetrazoles

2017

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Flash vacuum pyrolysis (FVP) of azides is an extremely valuable method of generating nitrenes and studying their thermal rearrangements. The nitrenes can in many cases be isolated in low-temperature matrices and observed spectroscopically. NH and methyl, alkyl, aralkyl, vinyl, cyano, aryl and N-heteroaryl, acyl, carbamoyl, alkoxycarbonyl, imidoyl, boryl, silyl, phosphonyl, and sulfonyl nitrenes are included. FVP of triazoloazines generates diazomethylazines and azinylcarbenes, which often rearrange to the energetically more stable arylnitrenes. N elimination from monocyclic 1,2,3-triazoles can generate iminocarbenes, 1H-azirines, ketenimines, and cyclization products, and 1,2,4-triazoles are precursors of nitrile ylides. Benzotriazoles are preparatively useful precursors of cyanocyclopentadienes, carbazoles, and aza-analogues. FVP of 5-aryltetrazoles can result in double N elimination with formation of arylcarbenes or of heteroarylcarbenes, which again rearrange to arylnitrenes. Many 5-substituted and 2,5-disubstituted tetrazoles are excellent precursors of nitrile imines (propargylic, allenic, or carbenic), which are isolable at low temperatures in some cases (e.g., aryl- and silylnitrile imines) or rearrange to carbodiimides. 1,5-Disubstituted tetrazoles are precursors of imidoylnitrenes, which also rearrange to carbodiimides or add intramolecularly to aryl substituents to yield indazoles and related compounds. Where relevant for the mechanistic understanding, pyrolysis under flow conditions or in solution or the solid state will be mentioned. Results of photolysis reactions and computational chemistry complementing the FVP results will also be mentioned in several places.

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Section: Azidesmentioning

confidence: 97%

Section: Azidesmentioning

confidence: 99%

Section: Azidesmentioning

confidence: 99%

Section: Imidoyl Azides [Rc(nr′)−n 3 ] and Imidoylnitrenes [R(cnr′)−n]mentioning

confidence: 99%

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Flash Vacuum Pyrolysis of Azides, Triazoles, and Tetrazoles

2017

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“…There is very little direct spectroscopic evidence for the existence of imidoylnitrenes, but it is noted that weak, broad absorptions observed around 520 nm on laser flash photolysis of 5-phenyltetrazole and 1-methyl-5-phenyltetrazole may be due to the benzimidoylnitrenes . Despite the shortage of direct evidence, imidoylnitrenes are very frequently postulated as reactive intermediates in pyrolyses and photolyses of 1-aryltetrazoles 6′ , where they typically cyclize onto the benzene rings to afford benzimidazoles and related compounds. − Ring cleavage reactions with formation of carbodiimides or cyanamides have also been thoroughly investigated. − …”

Section: Introductionmentioning

confidence: 99%

Imidoylnitrenes R′C(═NR)–N, Nitrile Imines, 1H-Diazirines, and Carbodiimides: Interconversions and Rearrangements, Structures, and Energies at DFT and CASPT2 Levels of Theory

Bégué¹,

Silva²,

Dargelos³

et al. 2017

J. Phys. Chem. A

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The structures, energies, and rearrangements of imidoylnitrenes H-C(═NH)-N, HN-C(═NH)-N, Ph-C(═NH)-N, H-C(═NPh)-N, and MeO-C(═NCN)-N (10a-e) are investigated at DFT and CASPT2 levels of theory. Imidoylnitrenes are potentially formed by pyrolysis or photolysis of azides, tetrazoles (6, 6'), or sydnones. Unlike most acylnitrenes, the imidoylnitrenes 10 have triplet ground states. The first excited states are the open-shell singlets (OSSs), lying between ca. 4 and 20 kcal mol above the triplets at the CASPT2 level. The second excited states are the closed-shell singlets (CSSs), lying >50 kcal mol higher in energy. The OSS imidoylnitrenes can ring-close to 1H-diazirines 9 with very low activation energies (2-12 kcal mol), and the 1H-diazirines can then rearrange to nitrile imines 8 with activation energies of 37-48 kcal mol. Conversely, nitrile imines generated directly by pyrolysis or photolysis of 2,5-substituted tetrazoles 6 can rearrange to 1H-diazirines 9 and imidoylnitrenes 10 with activation energies of 37-60 kcal mol. Finally, the imidoylnitrenes 10 can rearrange to carbodiimides 11 with modest activation barriers of 12-20 kcal mol. Calculated vibrational data, UV-vis spectra, and spin densities in the triplet states are also reported, and zero-field splitting parameters |D/hc| in the range 0.9-1 cm and nonzero |E/hc| values are predicted.

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Photolysis and Pyrolysis of Phenyltetrazoles: Formation of Phenylcarbodiimide, N‐Phenylnitrile Imine, Phenylnitrene, Indazole, and Fulvenallene

et al. 2019

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Photolysis of 1‐phenyltetrazole 2b at either 193 or 266 nm in a Ne matrix as well as flash vacuum pyrolysis (FVP) of the same compound with isolation of the products in Ne matrix generate phenylcarbodiimide PhN=C=NH 6 very efficiently as the principal product in an almost pure state. Minor amounts of phenyl azide 8 and 1‐azacyclohepta‐1,2,4,6‐tetraene 10, the product of ring expansion of phenylnitrene, are also formed, and the amounts of both substances increase as a function of photolysis time. The photolysis of 2‐phenyltetrazole 1b in a Ne matrix at 266 nm for 0.5 min generates the allenic N‐phenylnitrile imine PhN=N(+)=CH(–) 3b, absorbing strongly and cleanly at 2021 cm–1 in the IR spectrum. At longer photolysis times peaks ascribed to phenyl azide, phenylnitrene, 1‐azacycloheptatetraene, and phenylcarbodiimide 6 become prominent. FVP of 2‐phenyltetrazole yields indazole 15 as the major product together with a small amount of phenylcarbodiimide 6. Indazole formation is ascribed to cyclization of the nitrile imine in the ground state. It is not formed on FVP of 1‐phenyltetrazole in agreement with the computational result that the thermodynamically most favourable path for rearrangement of the putative N‐phenylimidoylnitrene 5b yields phenylcarbodiimide 6 rather than phenylnitrile imine 3b. Further pyrolysis of indazole affords a minor yield of fulvenallene 18.

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Pyrolysis of annelated hexa- and heptamethylene-tetrazoles: Formation of 9- and 10-membered cyclic carbodiimides

Cited by 9 publications

References 20 publications

Flash Vacuum Pyrolysis of Azides, Triazoles, and Tetrazoles

Flash Vacuum Pyrolysis of Azides, Triazoles, and Tetrazoles

Imidoylnitrenes R′C(═NR)–N, Nitrile Imines, 1H-Diazirines, and Carbodiimides: Interconversions and Rearrangements, Structures, and Energies at DFT and CASPT2 Levels of Theory

Photolysis and Pyrolysis of Phenyltetrazoles: Formation of Phenylcarbodiimide, N‐Phenylnitrile Imine, Phenylnitrene, Indazole, and Fulvenallene

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