Photorearrangements of 2,4-disubstituted phenyl esters

Bradshaw, Jerald S.; Loveridge, Elwood L.; White, Lowell

doi:10.1021/jo01275a025

Cited by 24 publications

(8 citation statements)

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“…This trend is consistent with other reports in which it has been shown that decarboxylation increases with ortho substitution and the imposition of a conformation similar to that of the transition state. 10, 22 The 4/5 ratios are equal to k 4 /k 5 , the ratios of the rate constants for the addition of an acyl radical to the 2-and 4-positions of the aryloxy radical. Like the ratio of decarboxylation to rearrangement products, it is also sensitive to increasing phenyl substitution on the methyl groups of the o-cresyl acylates-it increases from 2.4 for 1a to 11.0 for 1c-but probably for very different reasons: the ratios of decarboxylation to rearrangement products depend on reaction pathways of the excited singlet states of the esters, themselves, whereas the 4/5 ratios involve factors related to the motions of the radical pairs that emanate from lyses of the excited singlet states.…”

Section: Irradiations In Cyclohexanementioning

confidence: 99%

Photoreactions of substituted o-cresyl acylates in cyclohexane and in polyethylene films. The influences of intra- and inter-molecular ‘crowding’ effects

Chen

Weiss

2009

Photochem Photobiol Sci

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Photo-Fries rearrangements and associated photoreactions of four o-cresyl acylates were investigated in cyclohexane and in unstretched and stretched polyethylene (PE) films with different degrees of crystallinity. The esters differ in the number of phenyl substituents attached to the methyl group of the cresyl part and the length of the acyl chain. The influences of intramolecular structural factors and intermolecular environmental effects on the fates of the excited singlet states and the singlet state aryloxy/acyl radical pairs generated subsequently from them are explored. The results indicate that there are definable limits to the selectivity of the photoreactions of aryl esters that are dependent on their shapes and the ability of their environments to interact with them. Quantum yields for the reactions of the o-cresyl acylates were measured in cyclohexane and their values can be understood on the bases of a combination of conformational and electronic factors. The PE cavities holding the less globularly shaped o-cresyl acylates act as templates for the formation of the photoproducts: the ratios of the 2- and 4-position photo-Fries rearrangement products from o-cresyl acetate and 2-benzylphenyl acetate are higher when irradiated in films that are stretched or have higher film crystallinity; control by the PE cavities over the fates of the radical pairs is diminished for the o-cresyl acylate with two phenyl groups appended to the methyl of the cresyl part. The cavities of the PE films exert an interesting influence on the ability of the excited singlet states to undergo concerted decarboxylation reactions as well.

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Section: Irradiations In Cyclohexanementioning

confidence: 99%

Photoreactions of substituted o-cresyl acylates in cyclohexane and in polyethylene films. The influences of intra- and inter-molecular ‘crowding’ effects

Chen

Weiss

2009

Photochem Photobiol Sci

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“…Although efficient loss of carbon dioxide has been observed for a dihydro-santonin3 and for simple 7-butyrolactones in the vapor phase,4 carbon dioxide loss is ordinarily a minor pathway in the solution photochemistry of lactones5 and esters. 6 The model compounds chosen for study are shown in Scheme I.9 Qualitative and quantitative results of photolysis of the model compounds are shown in Table I and Scheme I.10 For all 7-phenyl-7-butyrolactones studied, the efficiency of carbon dioxide loss is good, with 5 = 0.03-0.18. However, in contrast to 7-phenyl-7-butyrolactone (la) ( 00, = 0.020), the a-and ß-phenyl isomers decarboxylate very inefficiently ( , < 0.001) indicating that efficient carbon dioxide loss requires phenyl substitution at the 7 position.…”

mentioning

confidence: 99%

Photodecarboxylation of benzyl esters

Givens¹,

Oettle²

1971

J. Am. Chem. Soc.

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furan at -70°g ave a mixture of substances separable by thin-layer chromatography. Acetylation of the slower moving diol in excess acetic anhydride containing sodium acetate at room temperature yielded a monoacetate (60%), mp 182-185°, whose ir (CHC13) and mass spectra were indistinguishable from those of natural vindorosine (1). Identity was confirmed by thin-layer chromatography using two different solvent combinations.

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“…38 The photochemistry of 2,4-disubstituted phenyl esters has been studied previously, and the photo-Fries rearrangement, cleavage and decarboxylation, as well as methoxy migration, are all known to occur with these substrates. 25 Curiously, practically no detailed study has been done on the photolysis of highly substituted aryl esters. However, our substrates, orthoand/or para-blocked aryl alkanoates 1 and 2, are most suitable for sorting out the complicated competing reaction paths and mechanisms, since the ortho-and para-substituents formally prevent the photo-Fries rearrangement, but yet allow the 'semi"-rearrangement to the transient cyclohexadienone species.…”

Section: Mechanism Of Decarboxylation and Fries Rearrangementmentioning

confidence: 99%

“…According to the same procedure as above, 1d was synthesized from 60% NaH (0.70 g, 18 mmol), mesitol (2.1 g, 15 mmol) and cyclopropanecarbonyl chloride (1.4 mL, 16 mmol) 12.87, 16.30, 20.88, 129.28, 129.91, 135.24, 145.97 and 172.79; m/z (EI) 204 (M ϩ , 48%), 136 (58), 121 1(4), 91 (13), 69 (100) and 41 (25).…”

Section: Mesityl Cyclopropanecarboxylate 1dmentioning

confidence: 99%

Acid-controlled photoreactions of aryl alkanoates: competition of transesterification, decarboxylation, Fries-rearrangement and/or transposition

Mori

Takamoto

Wada

et al. 2003

Photochem Photobiol Sci

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2,4,6-Trimethylphenyl (mesityl) cyclohexanecarboxylate 1c and related mesityl esters 1a,b and d-f were photodecarboxylated upon irradiation at 254 nm in neutral solvents to give alkylmesitylenes 15 in good yields. In contrast, in the presence of a catalytic amount of acid and a sufficient amount of alcohol, the same compounds underwent facile phototransesterification to afford the corresponding ester 9 and phenol 10 in almost quantitative yields. Photolyses of less-substituted aryl alkanoates such as 2,6-dimethylphenyl (xylenyl), phenyl, 4-methoxyphenyl (4-anisyl) and 4-methoxynaphthyl alkanoates 2-4 and 8 were also investigated to elucidate the reaction mechanism of acid-catalyzed phototransesterification. Irradiation of these esters afforded the corresponding photo-Fries rearrangement products 20-23 both in neutral and acidic acetonitrile with significant acceleration of the processes in the presence of acid. It was elucidated that the photolysis of the esters affords the geminate radical pair 28, which in turn recombines to cyclohexadienone intermediates 29 and 30. Added acid accelerates not only the nucleophilic attack of alcohol to 29 and 30 but also other processes. Prolonged irradiation of the esters in neutral solution led to skeletal rearrangements of the initial product, affording isomeric alkylbenzenes. The phototransposition of cyclohexylmesitylene 15c via benzvalene intermediates was, on the contrary, retarded under acidic conditions. These acid-controlled competitive photoreactions are representative examples, in which a catalytic amount of acid can alter the fate of reactive intermediates on both ground-state and excited-state surfaces.

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Photorearrangements of 2,4-disubstituted phenyl esters

Cited by 24 publications

References 0 publications

Photoreactions of substituted o-cresyl acylates in cyclohexane and in polyethylene films. The influences of intra- and inter-molecular ‘crowding’ effects

Photoreactions of substituted o-cresyl acylates in cyclohexane and in polyethylene films. The influences of intra- and inter-molecular ‘crowding’ effects

Photodecarboxylation of benzyl esters

Acid-controlled photoreactions of aryl alkanoates: competition of transesterification, decarboxylation, Fries-rearrangement and/or transposition

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