Photochemistry of Pyridine N-Oxides. Trapping of an Intermediate with Amines

Alekperov, Dzhamil; Albini, Angelo; Fasani, Elisa; Lohse, Christian

doi:10.3987/com-87-4267

Cited by 3 publications

(3 citation statements)

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“…Such biradical-type structures have previously been postulated for a related system. 6 We have optimized (M06/cc-pVTZ and MP3/cc-pVTZ) the stationary points along the reaction coordinate 6 → 9 → 10, and find that the barrier for the oxygen walk rearrangement 6 → 9 far exceeds the very small barrier for the electrocyclic ring opening 6 → 7 (8). Oxirane 9, once formed, should undergo an extremely rapid electrocyclic ring opening reaction, yielding 1,3,4-oxadiazepine 10 with a very small barrier of ∆H ǂ = 0.4 kcal mol -1 (MP3: 2.5 kcal mol -1 ).…”

Section: Calculation Resultsmentioning

confidence: 99%

“…21,22 Calculations were performed using the B3LYP, 23 M06, 24 and M06-2X, 25 functionals, Hartree-Fock theory, 25 second-order, 26 third-order, 27 and fourth-order Møller-Plesset perturbation theory, 28 coupled-cluster theory with single and double excitations (CCSD), 29 and coupled cluster theory with single and double excitations with perturbational treatment of triple excitations (CCSD(T)). 30 As a multireference method, CASSCF 31 was employed, using an active space of eight electrons in eight orbitals (CASSCF (8,8)). Basis sets used include the standard 6-31G(d) 32 and cc-pVTZ 33 basis sets.…”

Section: Methodsmentioning

confidence: 99%

“…4,5 The reaction mechanism has been postulated to proceed via bridged oxaziridine 2 and azoxepine 3, although diradical and nitrene intermediates have been invoked as well. 1,2,[6][7][8] The products of the photochemistry of pyridazine N-oxide 5 are better characterized, and although only low yields could be obtained, the formation of furan 13 and cyclopropene-3carbaldehyde 12 seems to be established. 9 These products point to the intermediate formation of carbene 11, and hence to the presence of diazo compound 8, which could again be formed via bicyclic oxaziridine 6 and diazoxepine 7.…”

Section: Introductionmentioning

confidence: 99%

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Detection and Identification of Reaction Intermediates in the Photorearrangement of Pyridazine N-Oxide: Discrepancies between Experiment and Theory

Wagner

et al. 2019

J. Org. Chem.

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Section: Calculation Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Detection and Identification of Reaction Intermediates in the Photorearrangement of Pyridazine N-Oxide: Discrepancies between Experiment and Theory

Wagner

et al. 2019

J. Org. Chem.

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Synthesis of Heteroaromatics via Rearrangement Reactions

Vivona

Buscemi

Pibiri

et al. 2009

Handbook of Synthetic Photochemistry

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The varied family of heteroaromatics contains a large fraction of organic compounds, many of which have found important applications in different fields. Many synthetic methodologies have been developed to obtain target systems and, among them, photochemical methods represent valid and elegant alternatives when the final targets are difficult to obtain through ground-state chemistry. In this chapter, we describe the photochemical synthesis of heteroaromatic compounds through rearrangement reactions, particularly via ring-transformations of heterocyclic precursors [1][2][3][4][5][6][7].A classification of all photoinduced heterocyclic ring-transformation reactions is quite difficult to achieve due to the large variety of mechanistic pathways, experimental conditions and affecting parameters. In some cases, the photochemical product and the starting substrate have the same heterocyclic nucleus. In this chapter, we will refer to such reactions, characterized by the identity of the starting and final ring, as ring-degenerate rearrangements.In general, photoinduced rearrangements of heterocycles leading to heteroaromatic compounds may involve ring-contraction, internal cyclization, ring-expansion, ring-opening or ring-closure, and ring-fragmentation processes. As for five-membered rings, two processes will be repeatedly quoted throughout this chapter:. The ring contraction-ring expansion route (RCRE), which explains the formal interchange between two adjacent ring-atoms. This results from the photoinduced cleavage of the weakest bond in the ring with formation of a three-membered ring intermediate. The latter is then converted, either thermally or photochemically, into the final five-membered heterocyclic product (see e.g., Scheme 12.22). . The internal cyclization-isomerization route (ICI), which involves the formation of a bicyclic species featuring a single bond between the ring-atoms in the 2-and 5-positions of the original heterocycle. Sigmatropic shifts then occur, leading to different bicyclic intermediates from which the final products will arise (see e.g., Scheme 12.2).Handbook of Synthetic Photochemistry. Edited

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