Sigmatropic rearrangements in 5-allyloxytetrazoles

Frija, Luís M. T.; Reva, Igor; Ismael, A.; Coelho, Daniela V.; Fausto, Rui; Cristiano, Maria Lurdes Santos

doi:10.1039/c1ob05460k

Cited by 16 publications

(15 citation statements)

References 36 publications

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“…Tautomerism has been extensively studied in a great variety of azoles [5][6][7][8] as well as in other similar systems, including tetrazoles. [9][10][11][12][13][14][15][16][17][18][19][20][21][22] In these studies, the preference for a specific a) Author to whom correspondence should be addressed. Electronic mail: reva@qui.uc.pt tautomer or tautomers at different proportions, according to the physical state of the compound, has been established.…”

Section: Introductionmentioning

confidence: 99%

Tetrazole acetic acid: Tautomers, conformers, and isomerization

Araujo-Andrade

Reva

Fausto

2014

The Journal of Chemical Physics

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Monomers of (tetrazol-5-yl)-acetic acid (TAA) were obtained by sublimation of the crystalline compound and the resulting vapors were isolated in cryogenic nitrogen matrices at 13 K. The conformational and tautomeric composition of TAA in the matrix was characterized by infrared spectroscopy and vibrational calculations carried out at the B3LYP/6-311++G(d,p) level. TAA may adopt two tautomeric modifications, 1H- and 2H-, depending on the position of the annular hydrogen atom. Two-dimensional potential energy surfaces (PESs) of TAA were theoretically calculated at the MP2/6-311++G(d,p) level, for each tautomer. Four and six symmetry-unique minima were located on these PESs, for 1H- and 2H-TAA, respectively. The energetics of the detected minima was subsequently refined by calculations at the QCISD level. Two 1H- and three 2H-conformers fall within the 0-8 kJ mol(-1) energy range and should be appreciably populated at the sublimation temperature (∼330 K). Observation of only one conformer for each tautomer (1ccc and 2pcc) is explained in terms of calculated barriers to conformational rearrangements. All conformers with the cis O=COH moiety are separated by low barriers (less than 10 kJ mol(-1)) and collapse to the most stable 1ccc (1H-) and 2pcc (2H-) forms during deposition of the matrix. On the trans O=COH surfaces, the relative energies are very high (between 12 and 27 kJ mol(-1)). The trans forms are not thermally populated at the sublimation conditions and were not detected in matrices. One high-energy form in each tautomer, 1cct (1H-) and 2pct (2H-), was found to differ from the most stable form only by rotation of the OH group and separated from other forms by high barriers. This opened a perspective for their stabilization in a matrix. 1cct and 2pct were generated in the matrices selectively by means of narrow-band near-infrared (NIR) irradiations of the samples at 6920 and 6937 cm(-1), where the first OH stretching overtone vibrations of 1ccc and 2pcc occur. The reverse transformations could be induced by irradiations at 7010 and 7030 cm(-1), transforming 1cct and 2pct back to 1ccc and 2pcc, also selectively. Besides the NIR-induced transformations, the photogenerated 1cct and 2pct forms also decay in N2 matrices back to 1ccc and 2pcc spontaneously, with characteristic decay times of hours (1H) and tens of minutes (2H). The decay mechanism is rationalized in terms of the proton tunneling. In crystals, TAA exists exclusively as 1H-tautomer. By contrast, the tautomeric composition of the matrix-isolated monomers was found to consist of both 1H- and 2H-tautomers, in comparable amounts. A mechanistic discussion of the tautomerization process occurring during sublimation, accounting also for the observed minor decomposition of TAA leading to CO2 and 5-methyl-tetrazole, is proposed.

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Section: Introductionmentioning

confidence: 99%

Tetrazole acetic acid: Tautomers, conformers, and isomerization

Araujo-Andrade

Reva

Fausto

2014

The Journal of Chemical Physics

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“…A library of 5-allyloxy-1-aryl-tetrazoles 2a-h and 4-allyl-1-aryl-tetrazole-5-ones 3b-h was studied to elucidate the behaviour of the compounds when subjected to electronically induced fragmentation in EI-MS. 5-allyloxy-1-aryl-tetrazoles 2 were prepared from the reaction of 5-chloro-1-aryl-tetrazoles 1 with the respective allyl alcohol in an alkaline medium, as depicted in Scheme 1. When heated neat, at 100 • C, allyl tetrazolyl ethers 2 rearrange to give exclusively the corresponding tetrazolones 3, the process occurring through a concerted [3,3 ]-sigmatropic isomerisation (Scheme 1) [31,32]. Hence, 4-allyl-1-aryl-tetrazole-5-ones 3 are prepared by thermal rearrangement of their 5-allyloxy-1-aryltetrazole precursors 2.…”

Section: Resultsmentioning

confidence: 99%

“…Molecules 2021, 26, x FOR PEER REVIEW 3 of 18 a concerted [3,3′]-sigmatropic isomerisation (Scheme 1) [31,32]. Hence, 4-allyl-1-aryl-tetrazole-5-ones 3 are prepared by thermal rearrangement of their 5-allyloxy-1-aryl-tetrazole precursors 2.…”

Section: Resultsmentioning

confidence: 99%

Substituent Effects on EI-MS Fragmentation Patterns of 5-Allyloxy-1-aryl-tetrazoles and 4-Allyl-1-aryl-tetrazole-5-ones; Correlation with UV-Induced Fragmentation Channels

2021

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1,4- and 1,5-disubstituted tetrazoles possess enriched structures and versatile chemistry, representing a challenge for chemists. In the present work, we unravel the fragmentation patterns of a chemically diverse range of 5-allyloxy-1-aryl-tetrazoles and 4-allyl-1-aryl-tetrazolole-5-ones when subjected to electron impact mass spectrometry (EI-MS) and investigate the correlation with the UV-induced fragmentation channels of the matrix-isolated tetrazole derivatives. Our results indicate that the fragmentation pathways of the selected tetrazoles in EI-MS are highly influenced by the electronic effects induced by substitution. Multiple pathways can be envisaged to explain the mechanisms of fragmentation, frequently awarding common final species, namely arylisocyanate, arylazide, arylnitrene, isocyanic acid and hydrogen azide radical cations, as well as allyl/aryl cations. The identified fragments are consistent with those found in previous investigations concerning the photochemical stability of the same class of molecules. This parallelism showcases a similarity in the behaviour of tetrazoles under EI-MS and UV-irradiation in the inert environment of cryogenic matrices of noble gases, providing efficient tools for reactivity predictions, whether for analytical ends or more in-depth studies. Theoretical calculations provide complementary information to articulate predictions of resulting products.

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“…33 Calculations at DFT level predict that in all conformers the phenyl and tetrazole rings have planar geometries and are coplanar to each other (dihedral angle A). The exchange of the substituent X (H or CH 3 ) does not influence this parameter.…”

Section: Theoretical Analysis Of Proposed Routes; Interpretation Of Smentioning

confidence: 99%

“…Besides, 5-allyloxy-1-aryl tetrazoles 3 are prepared in high yields from the reaction of the required allylic alcohol 2 with 5-chloro-1-phenyl tetrazole 1 29 and 1-allyl-4-aryltetrazolones 4 are obtained from 5-allyloxy-1-aryl tetrazoles 3, in quantitative yields, through a thermally-induced sigmatropic isomerisation that proceeds via a concerted [3,3′]-sigmatropic Claisen-type mechanism. [30][31][32][33] Considering the relevance of pyrimidinones as scaffolds in heterocyclic synthesis 34 and the importance of developing mild and efficient synthetic routes to these compounds, we aimed at a deeper investigation of the scope of this photochemically based synthetic methodology. In particular, we propose to study the effect of steric constraints imposed by bulky allylic moieties on photoproduct selectivity and stability.…”

Section: Introductionmentioning

confidence: 99%

Photochemistry of 1-allyl-4-aryltetrazolones in solution; structural effects on photoproduct selectivity

Ismael

Serpa

Cristiano

2013

Photochem Photobiol Sci

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The photochemistry of tetrazolones derived from the carbocyclic allylic alcohols cyclohex-2-enol and 3-methylcyclohex-2-enol and from the natural terpene alcohol nerol was investigated in solution with the aim of assessing the effect of solvent and of structural constraints imposed by bulky allylic moieties on photoproduct selectivity and stability. Photolysis of tetrazolones derived from nerol and cyclohex-2-enol afforded the corresponding pyrimidinones as major products through a pathway that appears to be similar to that proposed for other 1-allyl-4-phenyl-1,4-dihydro-5H-tetrazol-5-ones derived from acyclic and unhindered allylic alcohols previously investigated but photolysis of the tetrazolone derived from the bulkier 3-methylcyclohex-2-enol 4c leads to formation of a benzimidazolone, indicating that, in this case, cyclization of the biradical formed upon extrusion of N 2 involves the phenyl substituent and not the allylic moiety. Theoretical calculations (DFT(B3LYP)/3-21G*) were conducted to support the interpretation of the experimental results and mechanistic proposals. Laser flash photolysis experiments were conducted with the aim of clarifying the nature of the intermediate involved in the primary photocleavage process.

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Sigmatropic rearrangements in 5-allyloxytetrazoles

Cited by 16 publications

References 36 publications

Tetrazole acetic acid: Tautomers, conformers, and isomerization

Tetrazole acetic acid: Tautomers, conformers, and isomerization

Substituent Effects on EI-MS Fragmentation Patterns of 5-Allyloxy-1-aryl-tetrazoles and 4-Allyl-1-aryl-tetrazole-5-ones; Correlation with UV-Induced Fragmentation Channels

Photochemistry of 1-allyl-4-aryltetrazolones in solution; structural effects on photoproduct selectivity

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