Recently Reported Crystalline Isothiazole Carbenes: Myth or Reality

DeHope, Alan; Lavallo, Vincent; Donnadieu, Bruno; Schoeller, Wolfgang W.; Bertrand, Guy

doi:10.1002/anie.200702272

Cited by 21 publications

(10 citation statements)

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“…However, following the report of the first isolated crystalline five-membered ring carbene [R = 1,3-di(1-adamantyl)imidazol-2-ylidene, 1 ] by Arduengo and co-workers, other stable heterocyclic carbenes have been synthesized. These include 1,2,4-triazol-5-ylidenes ( 2 , R = alkyl, aryl), 1,3-thiazol-2-ylidenes ( 3 , R = alkyl, aryl), , and 1,2-thiazol-3-ylidenes (isothiazol-3-ylidenes, 4 , Figure ) . The singlet carbene [ 1 , X = H, R = 1,3-di(1-adamantyl)] is thermodynamically stabilized by resonance and kinetically stabilized by the bulky 1-adamantyl groups adjacent to the carbene carbon.…”

Section: Introductionmentioning

confidence: 99%

Substituent Effects on Singlet−Triplet Gaps and Mechanisms of 1,2-Rearrangements of 1,3-Oxazol-2-ylidenes to 1,3-Oxazoles

et al. 2008

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Electronic structures, partial atomic charges, singlet-triplet gaps (Delta E ST), substituent effects, and mechanisms of 1,2-rearrangements of 1,3-oxazol-2-ylidene ( 5) and 4,5-dimethyl- ( 6), 4,5-difluoro- ( 7), 4,5-dichloro- ( 8), 4,5-dibromo- ( 9), and 3-methyl-1,3-oxazol-2-ylidene ( 10) to the corresponding 1,3-oxazoles have been studied using complete-basis-set methods (CBS-QB3, CBS-Q, CBS-4M), second-order Møller-Plesset perturbation method (MP2), hybrid density functionals (B3LYP, B3PW91), coupled-cluster theory with single and double excitations (CCSD) and CCSD plus perturbative triple excitations [CCSD(T)], and the quadratic configuration interaction method including single and double excitations (QCISD) and QCISD plus perturbative triple excitations [QCISD(T)]. The 6-311G(d,p), 6-31+G(d,p), 6-311+G(d,p), and correlation-consistent polarized valence double-xi (cc-pVDZ) basis sets were employed. The carbenes have singlet ground states, and the CBS-QB3 and CBS-Q methods predict Delta E ST values for 5- 8 and 10 of 79.9, 79.8, 74.7, 77.0, and 82.0 kcal/mol, respectively. CCSD(T), QCISD(T), B3LYP, and B3PW91 predict smaller Delta E ST values than CBS-QB3 and CBS-Q, with the hybrid density functionals predicting the smallest values. The concerted unimolecular exothermic out-of-plane 1,2-rearrangements of singlet 1,3-oxazol-2-ylidenes to their respective 1,3-oxazoles proceed via cyclic three-center transition states. The CBS-predicted barriers to the 1,2-rearrangements of singlet carbenes 5- 9 to their respective 1,3-oxazoles are 41.4, 40.4, 37.8, 40.4, and 40.5 kcal/mol, respectively. During the 1,2-rearrangements of singlet 1,3-oxazol-2-ylidenes 5- 9, there is a decrease in electron density at oxygen, N3 (the migration origin), and C5 and an increase in electron density at C2 (the migration terminus), C4, and the partially positive migrating hydrogen.

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Section: Introductionmentioning

confidence: 99%

Substituent Effects on Singlet−Triplet Gaps and Mechanisms of 1,2-Rearrangements of 1,3-Oxazol-2-ylidenes to 1,3-Oxazoles

et al. 2008

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“…8 Importantly, in contrast to regular carbenes, no obvious dimerization pathway can be foreseen, and therefore it was reasonable to believe that unhindered MICs with various heteroatom-containing skeletons could be stable. To test this hypothesis, we attempted the preparation of 1,3-dithiol-5ylidenes F, but observed a spontaneous ring opening yielding the corresponding ethynyl dithiocarbamate G. 9 The formation of G is reminiscent of the ring-opening reaction observed in the deprotonation of isothiazolium salts, 10 and therefore is probably due to the weakness of the sulfur-carbon bond. These results prompted us to investigate the preparation of thiazol-5-ylidenes H, since a similar ring-opening process would imply the cleavage of a carbon-nitrogen bond.…”

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confidence: 99%

Mesoionic thiazol-5-ylidenes as ligands for transition metal complexes

et al. 2011

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“…Ylides of type 8, 2 aryl 4,5 di phenylisothiazolylidenes described as stable 15 in fact re arrange into 2 arylideneimino 3,4 diphenylthietanes un der conditions of their synthesis, 16 which the authors of the work 15 agreed on. 17 Azolium cations and cationic      complexes.…”

Section: Resultsmentioning

confidence: 91%

Quantum chemical studies of azoles 2. Thermodynamic stability of neutral molecules and intermediates formed during electrophilic substitution of 1,2- and 1,3-azoles

2014

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The thermodynamic stability of 1,2 and 1,3 azole molecules, as well as of cationic and bipolar (carbenoid) intermediates in the gas phase and in aqueous solution formed by electro philic substitution (proton as a model electrophile) was compared based on the analysis of quantum chemical calculations performed at the DFT/B3LYP/6 31G(D) level of theory with zero point energy corrections. The differences in the chemical behavior of the isomeric 1,2 and 1,3 azole pairs, viz., pyrazole-imidazole, isoxazole-oxazole, and isothiazole-thiazole, were considered.Key words: 1,2 azoles, 1,3 azoles, electrophilic substitution, quantum chemical calcula tions, DFT/B3LYP/6 31G(D) method.In the previous communication, 1 we considered and discussed the results of quantum chemical calculations of 1,2 and 1,3 azoles, as well as of the intermediates that are formed via two alternative mechanisms of electrophilic substitution: the normal addition-elimination mechanism with the formation of intermediate cationic  complexes and the elimination-addition mechanism specific to azoles with the participation of ylide (carbene) intermedi ates. Such an ylide substitution is especially characteristic of 1,3 azoles; the corresponding experimental data is sum marized in the review. 2 The goal of the present work is to analyze the results of quantum chemical calculations reported previously 1 in or der to determine the relative thermodynamic stability of 1,2 and 1,3 azole molecules, as well as of cationic and bipolar (carbenoid) intermediates formed during electro philic substitution (proton as a model electrophile), and to consider the differences in the chemical behavior of isomeric 1,2 and 1,3 azole pairs: pyrazole-imidazole, isoxazole-oxazole, and isothiazole-thiazole. Structures 1-10, which characterize the transformation of the starting 1,3 and 1,2 azoles 1 and 6 into ylide substitution inter mediates 2-5 and 7-10, are shown in Scheme 1 and those related to the transformation of the same azoles 1 and 6 into the intermediates of the traditional addition-eli mination mechanism (cationic  complexes 11-16) are shown in Scheme 2. Quantum chemical methodIn the present work, we used the results of our quantum chemical calculations 1 done in terms of the density functional theory (DFT) using the B3LYP functional and the 6 31G(D) basis set with zero point energy corrections taking into account solvation effects using the overlapping sphere model (IEFPCM). 3 The appropriateness of this relatively simple DFT method with a modest basis set was justified in the work. 1 Thus, the results of calculations performed with this method for five membered heterocycles containing one heteroatom are in good agreement with the data obtained by ab initio Hartree-Fock and MP2 4,5 methods, which showed the relationship between the substrate selectivity and the ability of the heteroatom to delocalize a posi tive charge (N > O > S) and between the positional selectivity in the electrophilic substitution reaction of pyrrole, furan, and thio phene and the change in the st...

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Recently Reported Crystalline Isothiazole Carbenes: Myth or Reality

Cited by 21 publications

References 50 publications

Substituent Effects on Singlet−Triplet Gaps and Mechanisms of 1,2-Rearrangements of 1,3-Oxazol-2-ylidenes to 1,3-Oxazoles

Substituent Effects on Singlet−Triplet Gaps and Mechanisms of 1,2-Rearrangements of 1,3-Oxazol-2-ylidenes to 1,3-Oxazoles

Mesoionic thiazol-5-ylidenes as ligands for transition metal complexes

Quantum chemical studies of azoles 2. Thermodynamic stability of neutral molecules and intermediates formed during electrophilic substitution of 1,2- and 1,3-azoles

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