A photo-induced rearrangement involving aryl participation (original) (raw)
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Photochemistry of 2-Alkoxymethyl-5-methylphenacyl Chloride and Benzoate
The Journal of Organic Chemistry, 2006
Irradiation of 2-(alkoxymethyl)-5-methyl-R-chloroacetophenones (1a-c) and 2-(methoxymethyl)-5methylphenacyl benzoate (1d) in dry, nonnucleophilic solvents afforded 3-alkoxy-6-methylindan-1-ones (3a-c) in very high chemical yields. 3-Methylisobenzofuran-1(3H)-one (2) was, however, isolated as a major photoproduct in the presence of trace amounts of water. Quenching experiments and laser flash spectroscopy revealed that the indanone derivatives 3 are formed by 1,5-hydrogen migration from the lowest triplet excited state of the acetophenones 1 and cyclization of the resulting photoenols. In contrast, production of the lactone 2 in wet solvents was found to result from two consecutive photochemical transformations. The photoenols produced by photolysis of 1a-c add water as a nucleophile to form 2-acetyl-4-methylbenzaldehyde (4), which is further converted to 2 via a second, singlet state photoenolization process. Exhaustive photolysis of 1a in methanol produced the acetal 2-(dimethoxymethyl)-5-methylacetophenone (7a) as the exclusive product. The remarkable selectivity of these photoreactions may well be useful in synthetic organic chemistry.
J Am Chem Soc, 1971
The photolysis in benzene of endo-5-benzoylbicyclo[2.1 .l]hexane (5) has been found to afford A3-cyclopentenylacetophenone (7) and 2-pheny1tricyclo[3.2.0.03~7]heptan-2-ol (8). Tricyclic alcohol 8 was found to rearrange thermally to A3-cyclopentenylacetophenone. In the presence of 90 x acetic acid, tricyclic alcohol 8 rearranged to give 2-phenyl-2-norbornen-exo-6-01 (ll), 2-phenyl-6-exo-acetoxy-2-norbornene (12), 2-phenyltricyclo-[2.2.1 .02 ?6]heptan-3-01 (13), and 2-phenyl-3-acetoxytricyclo[2.2.1 .0*t6]heptane (14). The photochemical transformations encountered in this work appear to be best described by a transannular hydrogen abstraction followed by subsequent reactions of the diradical thus formed. The photoreactions were shown to proceed by way of a triplet n-a* state. In striking contrast to the extraordinarily slow cyclobutylphenyl ketone system, both exo-and endo-5-benzoylbicyclo[2.1 .l]hexanes were found to rearrange at a faster rate than valerophenone. The inefficiency of these reactions (CP exo = 0.06, CP endo = 0.20) can be attributed to an unusually rapid triplet degradation. n the preceding paper, it was shown that the irradia-
The Journal of Organic Chemistry, 2019
Irradiation of a series of p-substituted aryl benzoates under N 2 atmosphere in homogeneous and micellar media was investigated by means of steady-state condition and of time-resolved spectroscopy. A notable selectivity in favor of the 2-hydroxybenzophenone derivatives was observed in micellar media. The benzophenone derivatives were the main photoproduct. On the other hand, in homogeneous media (cyclohexane, acetonitrile, and methanol) the observed product distribution was entirely different, viz. substituted 2hydroxybenzophenones, p-substituted phenols, benzyl and benzoic acid were found. The binding constants in the surfactant were also measured and NOESY experiments showed that the aryl benzoates were located in the hydrophobic core of the micelle. Laser flash photolysis experiments led to the characterization of both p-substituted phenoxy radical and substituted 2-benzoylcyclohexadienone transients in homogeneous and micellar environment. 50 lifetime in the restricted hydrophobic core of the micelle. For 51 example, geminate radical pairs that are produced photochemi-52 cally within the micellar core, have their rotational and 53 translational mobility constrained inside the micelles. 2 Indeed, 54 the mobility restricted within the hydrophobic cores of radicals, 55 radical cations, or other reactive intermediates limits unwanted 56 reactions (e.g., radical−radical self-quenching reactions) and the 57 access of adventitious reagents (e.g., water and oxygen) that 58 would cause their collapse in solution. Therefore, micellar 59 solution can induce a product distribution and a relative 60 chemical yield that can be significantly different when compared 61 with homogeneous conditions. 1,2 62 There have been many studies on the control of the reactivity 63 of radical species generated within the hydrophobic core of the 64 micelle, and some physical parameters (e.g., electrostatic, 65 polarity, hydrophobic interactions, viscosity, as well as hydro-66 gen-bonding solvation) may be involved in determining their 67 reactivities. 3 In addition, several studies directed to analyze and 68 quantify the reactivity, selectivity, and efficiency of micellar cage 69 on photochemical reactions in water have been carried out. 70 Among the vast number of photochemical transformations, a 71 particular example is represented by the photo-Fries rearrange-72 ment. Anderson and Reese 4 have discovered the photoreaction 73 where a homolytic fragmentation of a carbon−heteroatom bond
Journal of the American Chemical Society, 2008
J.Wirz@unibas.ch p-Hydroxyphenacyl is an effective photoremovable protecting group, not least due to the fast release of its substrates, accompanied by a photo-Favorskii rearrangement of compounds 1 to p-hydroxyphenylacetic acid (2) that is transparent down to 300 nm. First used for the release of ATP from 1 (X ) ATP) a decade ago, 1 the reaction has been employed in a variety of fields as diverse as neurobiology, 2 enzyme catalysis, 3 and biochemistry. 4 The nature and timing of the bond-making and bond-breaking events have not been fully elucidated despite extensive experimental and theoretical efforts by our group 5 and others. 6,7 We now report observation of the primary photoproduct, the triplet biradical 3 3, and of a new side product, p-hydroxybenzyl alcohol (6), that is formed by decarbonylation of the putative spirodione intermediate 4 at moderate water concentrations (Scheme 1). Solvent kinetic isotope effect (SKIE) studies by nanosecond laser flash photolysis (LFP) provide significant information on the role of water in the photo-Favorskii rearrangement of p-hydroxyphenacyl diethyl phosphate 1a to p-hydroxyphenylacetic acid (2).
Photochemical & Photobiological Sciences, 2003
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.
J Am Chem Soc, 1977
Although the photochemical behavior of the carbonyl group has received much scrutiny in the past d e~a d e ,~.~ relatively little is known about the photochemistry of the small amount of enol tautomer which exists in equilibrium with the keto In an earlier reportS dealing with the photorearrangement of 4-phenyl-3-chromanone (1) to 4-phenyldihydrocoumarin (2),6 evidence was presented which demonstrated that the enol content can be an overriding factor in determining the quantum efficiency of a photoreaction. As part of our continuing studies dealing with enol photoc h e r n i~t r y ,~~~ we have undertaken an investigation of the excited state behavior of the 4-carbomethoxy-3-chromanone (3) system. W e now report that in extending our studies to this system, we have discovered an unusual solvent effect which controls the product distribution. In addition, we have uncovered a n unprecedented photodecarbonylation reaction which can best be explained by invoking the intermediacy of a transient cyclopropanone.
Photoinduced Rearrangement of Aryl-Substituted Acylcyclohexasilanes
European Journal of Inorganic Chemistry, 2015
In the present study, we examined photochemical transformations of acylcyclohexasilanes (Me 3 Si) 2 Si 6 Me 12 (Me 3 Si)-COR (compounds 1) with aromatic substituents attached to the carbonyl C atom. When photolyzed at wavelengths above 300 nm in hydrocarbon solvents, 1a-c (1a: R = o-Tol; 1b: R = 2,3-Me 2 C 6 H 3 ; 1c: R = 2,4-Me 2 C 6 H 3 ) afforded the previously unknown eight-membered heterocyclopolysilanes 3a-c, which feature endocyclic Si=C double bonds with remarkable selectivity. If two ortho-alkyl groups are present at the aromatic ring (compounds 1d-f), the primary products of type 3 (3d: R = Mes; 3e: R = 1,6-Me 2 C 6 H 3 ; 3f: R = 2,4,6-iPr 3 C 6 H 2 ) are photochemically unstable and undergo intra-
Journal of the American Chemical Society, 1975
On irradiation cyclopentyl phenyl ketone has been found to rearrange principally t o l-phenyl-5-hexen-lone. Further irradiation affords l-phenyl-4-hexen-lone , l-phenyl-l-hydroxy-2-vinylcyclobutane, l-phenyl-3cyclohexen-1-01, a n d acetophenone. The photochemical transformations encountered in this work appear t o be best described by a transannular hydrogen abstraction followed by subsequent reactions of the diradical thus formed. T h e photorearrangement was shown t o proceed by way of a triplet n-T* state. In striking contrast to the extraordinarily slow a n d inefficient reaction in the cyclobutyl system, cyclopentyl phenyl ketone was found t o rearrange with high quantum efficiency and of the order of three powers of ten faster. pounds. XX.
Journal of the American Chemical Society, 1971
Mechanistic studies on the photorearrangements of benzobicyclo[2.2.2]octadienone (1) and bicyclo-[2.2.2]octenone (5) are reported. The limiting quantum yields for the singlet reaction of 1 are: &is = 0.50; @nsphthslene = 0.45; ~4,5-benLobie,c~o[l.l.0100ta-2,1-dion.8~0~~ = 0.10. The limiting quantum yields for the acetophenonesensitized reaction are: adis = 0.14; anaphthslene = 0.01 ; ~b e n r o t r i o y e l o [ 3 . 3 . 0 , 0 2~8~~~t e n~3 . 0 n e = 0.12. A deuterium labeling experiment established the 1,2-acyl migration mechanism for the photosensitized rearrangement of 1. Finally, it was shown that the triplet reaction proceeded by a concerted, symmetry-allowed process by comparison with the photoisomerization of lactone 12.
Canadian Journal of Chemistry, 2011
A broadly based investigation of the effects of a diverse array of substituents on the photochemical rearrangement of p-hydroxyphenacyl esters has demonstrated that common substituents such as F, MeO, CN, CO 2 R, CONH 2 , and CH 3 have little effect on the rate and quantum efficiencies for the photo-Favorskii rearrangement and the release of the acid leaving group or on the lifetimes of the reactive triplet state. A decrease in the quantum yields across all substituents was observed for the release and rearrangement when the photolyses were carried out in buffered aqueous media at pHs that exceeded the ground-state pKa of the chromophore where the conjugate base is the predominant form. Otherwise, substituents have only a very modest effect on the photoreaction of these robust chromophores.