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

Abstract

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...

An expedient route to heterocycles through α-arylation of ketones and arylamides by microwave induced thermal SRN1 reactions

“…Products 3a-k, 3m, 9a-c, 12, 14, and 15 are known compounds and present spectral data as shown in the literature, in agreement with the proposed structures. 1,2-Diphenylethanone (3a), 29 4-(2-oxo-2phenylethyl)benzonitrile (3b), 30 2-(4-methoxyphenyl)-1-phenylethanone (3c), 31 2-(4-uorophenyl)-1-phenylethanone (3d), 31 2-(4-nitrophenyl)-1-phenylethanone (3e), 32 2-(naphthalen-1-yl)-1-phenylethanone (3f), 33 2-(naphthalen-2-yl)-1-phenylethanone (3h), 34 1-phenyl-2-(pyridin-2-yl)ethanone (3i), 35 1-(4-methylphenyl)-2-phenylethanone (3j), 36 1-(4-aminophenyl)-2-phenylethanone (3k), 37 1-(4-chlorophenyl)-2-phenylethanone (3m), 36 1-(allyloxy)-2-iodobenzene (5), 16 2-(2-iodophenyl)-1-phenylethanone (9a), 21 2-(2-bromophenyl)-1-phenylethanone (9b), 38 2-(4iodophenyl)-1-phenylethanone (9c), 21 2-phenylcyclohexanone (12), 39 1-methyl-3-phenylindolin-2-one ( 14), 28 and 2-phenyl-1Hindole (15). 32 3-(2,3-Dihydrobenzofuran-3-yl)-1-phenylpropan-1-one (6) Following the general procedure, using tBuOK (179 mg, 0.75 mmol), acetophenone (0.75 mmol), and aryl halide 5 (0.25 mmol), microwave irradiation at 60 C for 10 min and then purication by radial chromatography (petroleum/ethyl ether, 8/2) provided 6 as light yellow crystals (18 mg, 29% yield).…”

Oxidative cleavage of 3-phenyllactic acid in presence of molybdenum complexes

“…On the basis of its MS, 1 H NMR and IR spectra, it was found to be 3,4-diphenyl-2,5-dihydrofuran-2-one, shortly denoted as lactone [24]. The isolated compound is in all respects identical to an independently prepared lactone [25,26]. In order to monitor the course of the reaction by 1 H NMR spectroscopy, two reaction mixtures were prepared in acetonitrile d 3 , one in argon and another in oxygen atmosphere.…”

Electrochemical generation of the azo linkage. Synthesis of bicyclic azo compounds, precursors of 1,3-diyls

“…etc. ), and modified prostaglandins,1 we required a route to bicyclic azo compounds (e.g., 2) subject to the following conditions: (1) reactions leading to 2 must be conducted at or below room temperature to avoid or at least minimize thermal decomposition of the product; (2) the reagents, reaction conditions, and byproducts must be compatible with the survival of the C7-C8 system for a variety of different substituents A and B; (3) the sequence should bypass the formation of hydrazo compounds since they are often unstable. Furthermore, the conditions used to effect their conversion to azo compounds are often incompatible with the survival of the product; (4) the sequence must (obviously) be efficient.…”

“…The method, illustrated in eq 1, utilizes a controlled-potential reductive cleavage of a R -CH,CCI, bis(2,2,2-trichloroethyl) dicarbamate followed by oxidation using aqueous potassium ferricyanide at 0 °C. Undoubt- (1) Tricyclopentanoids, see: (a) Little, R. D.; Bukhari, A.; Venegas, M. G. Tetrahedron Lett. 1979, 305-8.…”

“…In light of recent interest in -lactone systems, namely, Padwa's investigation of migratory aptitude in the photochemical rearrangement of 2(5H)-furanone1 and Tidwell's work on cyclization by radical displacement on es4er groups and conversion of acetals to lactones,2 we wish to report the radical rearrangement of the lactone, 5-(tertbutylperoxy)-3,4,5-triphenyl-2(5H)-furanone (1). In the course of seeking a route to /3-aroylvinyl radicals,3 we presumed that the decomposition of 1 under nitrogen in bromobenzene would lead to the oxy-2(5H)-furanone radical 2.…”