Photochemical decarboxylation

Another major route to fluorinated organomercury compounds is thermal or photochemical decarboxylation offluonne-conlaining mercury carboxylates [/-Si, 169, 170,171, 172], as shown for example in equation 125 [153, 169] Via similar methodology, C6HjHgCF3 (60-75%) [171], (CF3)2Hg (92%) [/i59T, (02NCFCl)2Hg (58%) [172], and [(CF3)3C]2Hg (80%) [157] were synthesized, and several of these mercurials have been used as fluorocarbene precursors [166],... 

It has been reported that 1 l//-dibenzo[h,< ][ ,4]dioxepin-l 1-one (dep-sidone) (243) undergoes photochemical decarboxylation and yields dibenzo-furan (59%) on irradiation with a high-pressure mercury lamp. The authors do not report whether the irradiation was conducted through silica or borosilicate glass. 

Poupko R, Rosenthal I, Elad D (1973) Photochemical decarboxylation of amino acids in the presence of metal ions. Photochem Photobiol 17 395-402... 

Griesbeck, A.G., Henz, A., Kramer, W., Lex, J., Nerowski, F., and Oelgemoller, M. (1997) Synthesis of medium- and large-ring compounds initiated by photochemical decarboxylation of W-phthalimidoalkanoates. Helvetica Chimica Acta, 80, 912-933. 

Bridgehead carboxylic acids, e.g. adamantane-1-carboxylic acid, are transformed into acyl hypoiodites, followed by photochemical decarboxylation to yield the corresponding bridgehead iodides1091. 

Photochemical decarboxylation results in the formation of 2,3-dihydrothiazol-2-ylidene which reverts back to its thermodynamically stable isomer thiazol either under prolonged radiation at 250 20 nm or upon warming. 

Efficient preparative sequences involving radical decarboxylation followed by carbon-nitrogen bond formation are rare. Acyl nitrates decompose at elevated temperatures to give nitroalkanes (equation 46), but are unfortunately explosive and have to be prepared in situ and stored in solution. A noteworthy exception is found in the thermal or photochemical decarboxylation of tetrahydro-l,2-oxazine-3,6-diones leading to -lactams (equation 47). Doubtless a key factor in this reaction, considered to proceed via a radical cage mechanism, is the intramolecular nature of the carbon-nitrogen bond formation. 

Decarbonylation and Decarboxylation - The photochemical reactions between carboxylic acids such as formic and trifluoroacetic acid and silica surfaces have been studied. The irradiation of diphenylacetic acid in acetonitrile with acridine results in the decarboxylation and the formation of the adduct (102). When the two achiral compounds, acridine and diphenylacetic acid, are cocrystallized a chiral two component molecular crystal is obtained in which the components are present in a 1 1 ratio. Both (—)- and (+)- crystals can be obtained. This crystalline material is photochemically reactive and irradiation brings about decarboxylation and formation of the adduct (102) with an ee of 35%. This compound is accompanied by a low yield of (103) which is formed exclusively on irradiation of the reactants in acetonitrile solution.Photochemical decarboxylation can be brought about by the irradiation of benzilate (104)/ methyl viologen pairs. ... 

Decarboxylation of (175) occurs on its irradiation in an argon matrix at 10 K using 254 nm light. Spectroscopic analysis of the resulting matrix indicates the presence of a complex between carbon dioxide and the carbene (176). Tiaprofenic acid (177) undergoes facile photochemical decarboxylation, and this is reported to take place from an upper triplet excited state." A study of the transient photochemistry of 5-(p-toluyl)-l-methyl-2-pyrrolylacetic acid has been reported. Decarboxylation results in the formation of a carbanion in its triplet state. A laser-flash study using irradiation at 266 nm of the xanthene-9-carboxylate (178) has shown that the radical (179) is formed. This study used NaY zeolites and studied the oxidation of the radical within the cage structure. Calculations have indicated that decarboxylation of (180) and (181) and deprotonation of cycloheptatriene and cyclopentadiene affords the same anions (182) and (183), respectively. ... 

Two pathways can be considered to explain the formation of the [3]rotane derivative either addition of the carbene to methyl acrylate to give a y-lactone which subsequently undergoes thermal or photochemical decarboxylation, or initial decarboxylation of the dispiro-y-lac-tonylidene to a dispiro[2,0.2.1]hept-7-ylidene which is then trapped by methyl acrylate to give the product. 

However, Baeyer-Villiger oxidation of trispiro[2.0.2,0.2.1]cyclodecan-7-one (7) gave the corresponding y-lactone 8 which did not undergo the expected thermal or photochemical decarboxylation. ... 

The benzoxazinone (107) deceu-bonylates to yield (108) on irradiation. Photodecarboxylation of (109) provides a route to exaltolide The photochemical decarboxylation of the lactones (110) provides a convenient method for the synthesis of 1-azabicyclobutemes (ill). The reaction is, however, restricted to those compounds with two aryl groups on C-2. The norbornadienone (112) has been produced in a matrix by the irradiation of the azo compound (113). These authors point out that the outcome of the irradiation is dependent to a large extent on the material of which the matrix is composed. ... 

A further use of Barton esters has been described as a path to enol ether radicals. The reaction involves the photochemical decomposition at 355 nm of the derivative (85). As part of an approach to the synthesis of a series of Kopsia alkaloids, the reductive decarboxylation of the derivative (86) was carried out. This involved irradiation of the Barton ester (86a) in the presence of t-BuSH. This affords the product (86b). The photochemical decomposition of the Barton ester (87) provides a path to the silyl derivatives (88). The nature of the trapping agent X is dependent on the conditions under which the reaction is carried out. Thus a variety of derivatives can be obtained using alcohols to afford ethers, or using ethanesulfonyl azide to give azides. The Barton esters (89) undergo the usual photochemical decarboxylation to afford ethenoyloxy radicals. Cyclization within these, in the presence of tributylstannane yields the lactones (90). ... 

A quantitative study of the photochemical decarboxylation of pyruvic acid (108) has shown that the formation of products, e.g. (109), is more efficient at lower pH. This effect is interpreted... 

The efficiency of the photochemical decarboxylation of arylacetlc acids to give arylmethyl carbanions has been shown to be greatly enhanced if a hydroxyl substituent is present on the... 

Making use of their recently developed photochemical decarboxylation of cis-fused y-lactones (diffuse Strasbourg sunlight), Ourisson et have converted the keto-lactone (316), derived from dihydro-6-epi-santonin, into-epi-maalienone (317). Further irradiation of (317) resulted in the formation of a-cyperene (318) and /J-cyperene (319). 

A route to cyclic peptide mimetics has been developed using the SET-induced photochemical cyclization of the phthalimide derivatives (119). This process affords the cyclized compounds (120) in excellent yields (85-91 %). Hydroxy-phthalimidines are the products formed from the photochemical decarboxylation of a series of alkyl carboxylates in the presence of V-substituted phthalimides. The photochemical addition of a-silyl electron-donor systems, such as Et2NCH2SiMe3, to V-methylthiophthalimide takes plaee in polar solvents such as acetonitrile. 

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