Photochemical transformations of small ring carbonyl compounds. 85. Solvent control of migratory aptitudes in the photochemical rearrangement of 2(5H)-furanones

Padwa, Albert; Brookhart, Todd; Dehm, David; West, Gary A.; Wubbels, Gene G.

doi:10.1021/ja00449a059

Cited by 5 publications

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“…Under these conditions the photochemical rearrangement of 1 -* 2 was completely suppressed. Attention was next turned to the photochemical behavior of 3,5,5-triphenyl-2(5//)-furanone (12). Irradiation of a dilute solution of this compound in benzene gave 3,4,5-triphenyl-2(5//)-furanone (13)16 as the initial photoproduct (78%); longer irradiation led to the formation of phenylphenanthro[9,10-c]furanone16 ( 14) in high yield.…”

Section: Resultsmentioning

confidence: 99%

“…We found that this system was perfectly stable to prolonged photolysis in both benzene and methanol. This observation would tend to indicate that the rearrangement of the 3,5,5-triarylfuranone system proceeds via a di-7r-methane mechanism.25 3,5,5-triphenyl (12) benzene 0.37 0.52 0.6 0.36 0.18 3,5-diphenyl-5-/?-anisyl (18) benzene 0.36 0.12 2.75 )/ . d From product ratios.…”

Section: Resultsmentioning

confidence: 99%

“…One additional system which was also studied involved the photochemistry of 3,5,5-triphenyl-4-methyl-2(5//)-furanone (48). This material was conveniently prepared by treating 2(5//)-furanone 12 with diazomethane and thermolyzing the initially produced diazabicyclooctenone 47. Furanone 48 could readily be separated from structure 49 by fractional crystallization.…”

Section: Armentioning

confidence: 99%

“…The relative kr values listed in Table II are based on the assumption that there is either no return of an intermediate to ground state or else that all of the lactones undergo the same fraction of such return. One additional point worth mentioning is that since we are interested in the rate of migration of a single aryl group, for statistical reasons the rate constant for the 3,5,5-triphenyl-2(5//)-furanone system (12) is halved.…”

Section: Armentioning

confidence: 99%

“…Found: C , 76.57; H, 6.42.Extended irradiation of this material in benzene or methanol gave only recovered starting material with no indication of any other photoproduct.Synthesis of 3,5,5-Triphenyl-4-methyl-2(5H)-furanone (48). T o a stirred solution containing 1.56 g of 3.5,5-triphenyI-2(5H)-furanone(12) in 50 mL of ether was added a solution containing I .O g of diazomethane in 100 m L of ether. The solution was allowed to stir at 25 OC for 3 days.…”

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Photochemical transformations of small ring carbonyl compounds. 101. Migratory aptitude studies in the photochemical rearrangement of 2(5H)-furanones

Padwa¹,

Brookhart²,

Dehm³

et al. 1978

J. Am. Chem. Soc.

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Irradiation of 3,5-diphenyl-S-aryl-2(5H)-furanones in benzene results in a novel rearrangement and affords a mixture of 3,4-diphenyI-S-aryl-and 3,S-diphenyl-4-aryl-2( 5H)-furanones. Phosphorescence, sensitization, and quenching studies confirm the involvement of a T-T* triplet state in these reactions. The rate constants of aryl group migration were determined from quenching studies using piperylene as a quencher. These were found to be 0.18 X lolo, 1.3 X 1O'O. and 0.9 X 10'O s-' for migration of phenyl, p-anisyl, and p-cyanophenyl. respectively. Thus, p-An and p -C N P h are more reactive migrating groups than phenyl by factors of 7.2 and 5.0 in benzene. The preferential migration ofp-anisyl over phenyl (16/ 1) and p-cyanophenyl ovcr phenyl (3.5/ I ) suggests that the excited state involved in benzene has significant odd-electron character on the :j carbon of the tuJ-unsaturated lactone moiety. A striking feature of these rearrangements is that a substantial crobsover in migratory aptitude occurs upon changing the solvent from ben7ene to inethanol. A iionniigratingp-anisyl group W;IS found to significant-I! accelerate the rate of phenyl migration in methanol. Whereas the migration ofp-anisyl in preference to phenxl in benzene is attributable to stabilimtion of the radical like free valence by the migrating group, the slight preference for migration of phenyl over p-anisyl in methanol may be attributed to stabilization of the electron deficicncy which develops at C5 by the nonmigrating p-anisql group. The above results serve to emphasize the important role that electron distribution plays in photochemical migratory processcs Light-induced transformations of five-membered enol lactones have been the subject of recent intensive These compounds undergo a facile decarbonylation when subjected to ultraviolet excitation and produce a,@unsaturated ketones as primary photoproducts. Chapman and McIntosh have previously noted that a critical requirement for clean photochemical cleavage of the acyl-oxygen bond is the presence of a double bond adjacent to the ether ~x y g e n .~ Stabilization of the incipient oxy radical was considered to be a determining factor in the photocleavage of this bond. In sharp contrast to the extensive studies concerned with the photochemistry of enol lactones. only scattered reports have appeared concerning the photochemical behavior of the related a,P-unsaturated y-lactone As part of a continuing program dealing with the photochemical transformations of unsaturated lactones,I0 we found that 5,5-diaryl-2( 5H)-furanones undergo aryl group migration when subjected to ultraviolet excitation." During the course of our studies with this system, we uncovered a striking crossover in the competitive migratory aptitudes of aryl groups which arises from a solvent alteration.12 As there are relatively few examples of excited state migratory aptitudes being controlled by solvent variation,I3 we decided to examine the photochemistry of this system in greater detail. We report here the results of this study w...

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%