Phototransposition Chemistry of Phenylisothiazoles and Phenylthiazoles. 1. Interconversions in Benzene Solution

Pavlik, James W.; Tongcharoensirikul, Pakamas; Bird, Nigel P.; Day, A. C.; Barltrop, J. A.

doi:10.1021/ja00085a008

Cited by 45 publications

(25 citation statements)

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“…These results indicate that 5-phenylisoxazole (4) does not phototranspose via path A in Scheme 1 to yield 3-phenylisoxazole (6), 2-phenyloxazole (7), or 4-phenyloxazole (8). Indeed, GC co-injection studies using authentic samples of these compounds confirmed that 6, 7, and 8 were not formed in this reaction.…”

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confidence: 82%

Photochemistry of 4- and 5- phenyl substituted isoxazoles

Pavlik

Martin

Lambert

et al. 2005

Journal of Heterocyclic Chemistry

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5-Phenylisoxazole (4) and 4-phenylisoxazole (22) underwent phototransposition to 5-phenyloxazole (5) and 4-phenyloxazole (24) respectively. Labeling with deuterium or methyl confirmed that these phototranspositions occurred via the P 4 pathway which involves only interchange of the N2 and C3 ring position. Thus, 4-deuterio-5-phenylisoxazole (4-4d), 4-methyl-5-phenylisoxazole (10), and 5-methyl-4-phenylisoxazole (23) phototransposed to 4-deuterio-5-phenyloxazole (5-4d), 4-methyl-5-phenyloxazole (11), and 5-methyl-4-phenyloxazole (25) respectively. In addition to phototransposition, isoxazoles 4, 10, and 23 also underwent photo-ring cleavage to yield benzoylacetonitrile (9), α-benzoylpropionitrile (15), and aceto-α-phenylacetonitrile (26) respectively. Irradiation of 5-phenyl-3-(trifluoromethyl)isoxazole (16) in acetonitrile led to 5-phenyl-2-(trifluoromethyl)oxazole (17), the P 4 phototransposition product. Irradiation of 16 in methanol led to a substantial decrease in the yield of 17 and to the formation of a mixture of (E) and (Z)-2-methoxy-2-(trifluoromethyl)-3-benzoylaziridines 18a and 18b.

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confidence: 82%

Photochemistry of 4- and 5- phenyl substituted isoxazoles

Pavlik

Martin

Lambert

et al. 2005

Journal of Heterocyclic Chemistry

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“…[13,14] A recent study of femtosecond dynamics as well as theoretical calculations of pyridine by Zewail and Chachisvilis [5] explored the photochemical dynamics of the S 2 (pp*) excited state leading to formation of the azaprefulvene isomer. The reaction path on the S 2 (pp*) potential energy surface (PES) was found to be the lowest path for the formation of the azaprefulvene isomer at the CASSCF(8,7)/ STO-3G level.…”

Section: Introductionmentioning

confidence: 99%

Theoretical Characterization of Photoisomerization Channels of Dimethylpyridines on the Singlet and Triplet Potential Energy Surfaces

2001

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Photoexcitations and photoisomerizations due to low-lying n pi* and pi pi* excited states of dimethylpyridines are investigated by density functional theory, CASSCF, CASPT2 and MRCI methodologies. Mechanistic details for the formation of Dewar dimethylpyridines and the interconversions of dimethylpyridines are rationalized through the characterization of minima and transition states on the singlet and triplet potential energy surfaces of relevant intermediates. Our present theoretical schemes suggest that Mobius dimethylpyridine intermediate 14 and azabenzvalene intermediate 10 can serve as possible precursors to Dewar dimethylpyridines and singlet phototransposition products, respectively. The calculations suggest that an S1(pi pi*)/S0 conical intersection in dimethylpyridines 2 is involved in the formation of 14. An azabenzvalene 10 might be formed through S2(pi pi*)/S1(n pi*) interaction followed by an S1/S0 decay in dimethylpyridine 6. Calculated barriers of isomerizations from 14 to Dewar dimethylpyridine 7 and from 10 to 4 are 8.4 and 28.5 kcal mol(-1) at the B3LYP/6-311 G** level, respectively. In the suggested triplet multistage transposition mechanism, an out-of-plane distorted geometry 19 due to vibrational relaxation of the T1(3B1) excited state of 3,5-dimethylpyridine 6 is a precursor of the interconversion of 6 to 2.4-dimethylpyridine 4. The formation of a triplet azaprefulvene 21 with a barrier of 20.7 kcal mol(-1) is a key step during the triplet migration process leading to another out-of-plane distorted structure 27. Subsequent rearomatization of 27 completes the interconversion of 6 with 4. Present calculations provide some insight into the photochemistry of dimethylpyridines at 254 nm.

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“…Under similar conditions, a migration of the substituents was also observed. Thus, the photochemical transformation of 26 yields mainly 27 and lower amounts of 28 . In the main reaction, the phenyl substituent migrates.…”

Section: Photochemical Heteroatom Isomerization Of Heterocyclic Compomentioning

confidence: 99%

“…Thus, the photochemical transformation of 26 yields mainly 27 and lower amounts of 28. [25] In the main reaction, the phenyl substituent migrates. In a computational study, it has been shown that bicyclic intermediates are involved (compare 6-8 in Scheme 1).…”

Section: Photochemical Heteroatom Isomerization Of Heterocyclic Compomentioning

confidence: 99%

Photochemical Rearrangements in Heterocyclic Chemistry

2019

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Heterocyclic compounds play an important role in many domains of chemistry. They are important structural elements in bioactive compounds. Photochemical reactions enable transformations of such compounds in a very convenient way. In many cases no chemical reagent is used. Members of one compound family can be transformed into members of another one. Three important types of photochemical rearrangements with heterocyclic compounds are discussed: Photochemical heteroatom isomerization involving heteroatoms and substituents, photochemical reactions involving hydrogen atom transfer (HAT) and photochemical electrocyclization.

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Phototransposition Chemistry of Phenylisothiazoles and Phenylthiazoles. 1. Interconversions in Benzene Solution

Cited by 45 publications

References 0 publications

Photochemistry of 4- and 5- phenyl substituted isoxazoles

Photochemistry of 4- and 5- phenyl substituted isoxazoles

Theoretical Characterization of Photoisomerization Channels of Dimethylpyridines on the Singlet and Triplet Potential Energy Surfaces

Photochemical Rearrangements in Heterocyclic Chemistry

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