Acetone as sensitizer

Figure 4. (a) High-field part of an ESR spectrum obtained after H-abstraction from 3-chlorotetrahydrofuran, 0.1 m, in aqueous solution, at pH 4, upon UV irradiation in a flow system at 276 K, 3 mM K2S2O8, and 0.3 M acetone as sensitizer (b) and (c) are simulated spectra calculated with a line width of 0.005 mT, centers marked by triangles [84]. 

The u.v.-induced addition of propan-2-ol to acetylene has been studied with and without acetone as sensitizer.168 The acetylene (241) undergoes photoaddition of isopropylamine and isopropyl ether to yield (242) and (243a) respectively.16 The same acetylene also reacts with ethyl 2-methylpropionate giving /rans-(243b) and the cyclic product (244). 

A mixture of adenine, 2-propanol, and acetone as sensitizer exposed 19 hrs. to y-rays from a Co-source 8-(2-hydroxy-2-propyl)adenine. Y 81%. F.e. and reactions, also with UV-irradiation, and nucleosides, s. H. Steinmaus, I. Rosenthal, and D. Elad, J. Org. Chem. 36, 3594 (1971). 

Benzophenone imide UV-irradiated 2 hrs. in isopropyl alcohol as H-donor -> benzhydrylamine. Y 81% as the hydrochloride. Also sec. amines from azo-methines, and addition of acetone as sensitizer, s. M. Fischer, B. 100, 3599 (1967). 

A mixture of tcirahydrofuran, diethyl maleate, and acetophenone exposed to UV-light or a few days to sunlight crude diethyl a-tetrahydrofurylsuccinale. Y 80%. F. e., also with benzophenone or acetone as sensitizers in lower yield, s. I. Rosenthal and D. Elad, Tetrahedron 23, 3193 (1967) addition of f. O-hetero-cyclics cf. J. Org. Ghem. 33, 805 (1968). 

Acetic anhydride, with 2-hep-tanone to give 3-n-butyl-2, 4-pentanedione, 51, 90 ACETIC FORMIC ANHYDRIDE, 50, 1 Acetone azine, 50, 2 ACETONE HYDRAZONE, 50, 2, 28 Acetophenone, 54, 93 as sensitizer for irradiation of bicyclo[2.2.1]hepta-2,5-diene to give quadricyclane,... 

It has been found that the rhodium catalyst is not nearly as sensitive to poisoning as platinum or palladium catalyst. The metal inlet tube to the reaction bottle was merely rinsed with acetone, followed by ethanol, and the rubber stopper was soaked in 30-40% sodium hydroxide solution overnight. 

Data on the influence of solvents as sensitizers in the vapor phase were collected for water, benzene, carbon tetrachloride, methanol, ethanol, formaldehyde, acetone, acetic add, acetic anhydride and methyl propionate (157). 

Nonconjugated dienes and polyenes have triplet photochemistry which may be considered to arise from intramolecular interaction of one excited double bond with an isolated ground-state double bond. For example, the photocyclization of enrfo-dicyclopentadiene can be effected using acetone as a sensitizer.286 Other more flexible 1,5-dienes, when sensitized to triplet states, cross couple to yield bicyclo[2.1.1]-hexane structures. For instance, triplet mercury atoms convert both 1,5-hexadiene and 1,5-cyclooctadiene to such structures.267 Irradiation of the cyclooctadiene in the presence of cuprous chloride produces the tricyclo derivative in good yield266 but recent evidence again indicates that this latter reaction may proceed via free-radical intermediates.269... 

In all cases but one, irradiation at 313 nm of solutions in acetone produced the same products as obtained from irradiation at 254 nm of solutions in acetonitrile. The exception is the para-cyano compound with n = I. Direct as well as sensitized irradiation produces the cyclooctatriene derivative via the ortho adduct. In acetone, however, the cyclooctatriene undergoes sensitized ring closure to give the angular tricyclic product. Direct irradiation gives the linear compound, as had been reported earlier by Gilbert and co-workers [104], The compound with Z = COOEt and n = 1 was also irradiated, but proved to be unreactive, as had also been found by Gilbert et al. [105] for the methyl ester. The compounds with four-atom tethers (n = 2) react much slower than those with three-atom tethers, but the initial [2 + 2] cycloaddition nevertheless proceeds efficiently. 

The deMayo-type photochemistry of 1,3-dioxin-4-ones has been beautifully applied by Winkler et al. to the synthesis of complex natural products. Substrate 133 gave under sensitized irradiation (with acetone as cosolvent) product 134 as single diastereoisomer (Scheme 6.47). The diastereoselectivity results from cyclic stereocontrol exerted by the two stereogenic centers in the spiro-bis-lactone part of the starting material. After installation of the furan, saponification and bond scission in a retro-aldol fashion generated a keto carboxylic add, which produced the natural product ( )-saudin (135) by simultaneous formation of two acetal groups [128]. 

The tricyclic compound shown in the following scheme underwent a 1,2-acyl shift (oxa-di-n-methane rearrangement) to form the tetracyclic compound upon irradiation in a Pyrex immersion well in degassed dry acetone as both a solvent as well as a sensitizer. On the... 

Dihydrogen telluride is an acid in aqueous solution and is comparable in strength with phosphoric acid. Tellurols, especially arenetellurols, are expected to be at least as acidic as dihydrogen telluride. Therefore, tellurols should react easily with alkali metal hydroxides to form alkali metal tellurolates. Because tellurols are difficult to prepare, alkali metal tellurolates are best obtained by methods which avoid the tellurols. Sodium and lithium tellurolates are the most frequently used tellurolates. Although the tellurolates are not as sensitive to oxidation as the tellurols, tellurolates are almost always used in situ and are prepared and stored under nitrogen. Sodium benzenetellurolate was isolated as a moisture-and air-sensitive, grey powder. Its solutions in tetrahydrofuran or acetone were found to be stable for months when kept under nitrogen6. 

Only with compounds (20o-q) are bicyclooctenones found which are unreactive either on direct excitation ( irr = 300 lun) or by triplet sensitization (acetone or acetophenone as sensitizer). On comparison of these exceptional cases with the substrates in Schemes S and 11, it becomes apparent that ODPM reactivity vs. inertness is influenced by very subtle differences in the substitution pattern. For example, shortening of the acetal chain of (20d) to R = Me for (24k>) renders a photoreactive substrate (20d 21d 90% yield) photochemically inert. ... 

Hence, a quick analysis might use LUMO energies from semi-empirical calculations for the analysis of the reduction of 3 (Scheme 3). Because the LUMO energy of acetone as model for site (a) in 3 is the lowest within the three electrophores, one must expect that an electron will be accepted at this site. This is indeed demonstrated in the PET reduction of 3 to a ketyl radical anionic intermediate using tri-ethylamine as sensitizer [8]. 

Phenyl-l,2,4-triazoline-3,5-dione also undergoes addition-abstraction reactions (e.g., with acetone ). As would be expected for such a species, it will oxidize alcohols to the corresponding aldehydes or ketones. This oxidation is especially mild (room temperature in benzene, chlorobenzene or ethyl acetate) and so is a valuable method of oxidizing, or preparing, compounds sensitive to acid, base, or heat. 

Reagents reactive solely toward the methionyl side-chain in native proteins have not been described to date. Selective conversion of the thioether to the sulfoxide derivative by photosensitized oxidation has been reported in a protein devoid of free thiol groups. The selective photosensitized oxidation employed methylene blue or hema-toporphyrin as sensitizers, and aqueous acetic acid (30-90% v/v), or acidic buffers at pH 2-6.5, as solvents (Scoffone et al. 1970). Anaerobic photo-oxidation in 4 M aqueous acetone has been reported to lead to the same result (Gennari and Jori 1970). Methionine can be regenerated from the sulfoxide by incubation with thiols (5 % aqueous j9-mercapto-ethanol at pH 8.0, for 24 hr under Nj Jori et al. 1968). 

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