Synthesis of Thieno[2,3‐<i>d</i>]pyrimidines via Microwave‐Assisted Thermolysis of 1‐(Thiophene‐2‐yl)‐1<i>H</i>‐tetrazoles

Soares, Maria I. L.; Melo, Teresa M. V. D. Pinho e; Fausto, Rui

doi:10.1002/slct.201601196

Cited by 8 publications

(5 citation statements)

References 35 publications

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“…As mentioned in the Introduction, N -arylimidoylnitrenes are frequently found to cyclize to benzimidazoles and related compounds. − Thus flash vacuum pyrolysis of 1-phenyltetrazoles yields benzimidazoles (Scheme ). The DFT calculations confirm cyclization of the OSS imidoylnitrene 10d to 3a H -benzimidazole 12d .…”

Section: Results and Discussionmentioning

confidence: 99%

“…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%

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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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Section: Results and Discussionmentioning

confidence: 99%

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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“…It would be interesting to try to overcome this problem by using the falling-solid flash vacuum pyrolysis methodology . Evidence for the formation of carbodiimides 334 as intermediates en route to compounds 335 in microwave-assisted solution thermolyses was also adduced. , …”

Section: Azidesmentioning

confidence: 99%

“…35 Evidence for the formation of carbodiimides 334 as intermediates en route to compounds 335 in microwave-assisted solution thermolyses was also adduced. 287,288 The imidoyl azide valence tautomers of the tetrazoles are not often observed in this chemistry, but they were observed in the reactions described in Scheme 46. The polymethylenetetrazoles have revealed very interesting pyrolysis chemistry.…”

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

confidence: 99%

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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“…Soares et al [ 36 ] reported a selective plus proficient technique for the construction of thieno[2,3‐d]pyrimidine derivatives as shown in Scheme 30. The intermediates for unusual transformation were synthesized from 2‐aminothiophene‐3‐carboxylates 92, triethyl orthoformate, and sodium azide in glacial acetic acid.…”

Section: Synthetic Strategiesmentioning

confidence: 99%

Microwave‐assisted diversified synthesis of pyrimidines: An overview

Kumar

2021

Journal of Heterocyclic Chem

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Pyrimidines and their hybrid molecules have continued to be a favorable area for organic chemists owing to their richness in natural and synthetic compounds with multifarious involvement in pharmaceuticals and polymers and act as ligands. Different novel and greener synthetic protocols were developed in the last decades, but microwave‐assisted synthetic protocols played a significant role in constructing pyrimidine and its derivatives. In this article, we summarized the microwave‐supported strategy for the construction of pyrimidine fused or linked/tethered with other heterocycles, polysubstituted pyrimidines, solid‐supported synthesis of pyrimidines, and ionic liquid‐catalyzed strategies for the synthesis of pyrimidine and its derivatives reported in the last decade. Solid‐supported protocols using resins and ionic liquid‐catalyzed strategies afforded the corresponding products with excellent yield by dual activation. In most of the reports, the microwave‐irradiated approach was compared with conventional/traditional heating and found better in terms of reaction time, yield, atom economy, adherence with green chemistry principles, and reduction in purification wastage. Various authors evaluated the in vitro potential of synthesized pyrimidine derivatives for antimicrobial and antimalarial potential, and found moderate to excellent biological activity.

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Synthesis of Thieno[2,3‐d]pyrimidines via Microwave‐Assisted Thermolysis of 1‐(Thiophene‐2‐yl)‐1H‐tetrazoles

Cited by 8 publications

References 35 publications

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

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

Flash Vacuum Pyrolysis of Azides, Triazoles, and Tetrazoles

Microwave‐assisted diversified synthesis of pyrimidines: An overview

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