Английская Википедия:1,3-Diphenylisobenzofuran
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1,3-Diphenylisobenzofuran is a highly reactive diene that can scavenge unstable and short-lived dienophiles in a Diels-Alder reaction. It is furthermore used as a standard reagent[1] for the determination of singlet oxygen,[2] even in biological systems.[3] Cycloadditions with 1,3-diphenylisobenzofuran and subsequent oxygen cleavage provide access to a variety of polyaromatics.
Preparation
The first synthesis of 1,3-diphenylisobenzofuran was reported in 1905 by A. Guyot and J. Catel.[4][5] Phenylmagnesium bromide was reacted with 3-phenylphthalide (the latter accessible from the methyl ester of 3-hydroxyphthalide with phenylboronic acid in 95% yield[6]) to a lactol, which gives with mineral acids upon elimination of water 1,3-diphenylisobenzofuran with 87% yield.[7]
The patent literature describes the preparation of 1,3-diphenylisobenzofuran by [4+2]cycloaddition of 1,3-butadiene and dibenzoylethylene (1,4-diphenyl-2-butene-1,4-dione, accessible from fumaryl chloride and benzene in the presence of aluminium chloride.[8]).[9] Dibenzoylethylene is predominantly present in the trans configuration[10] but it can be converted into the needed cis configuration by simple heating.[11]
The 4,5-dibenzoylcyclohexene formed previously is cyclized with acetic anhydride to the dihydroisobenzofuran. By bromine addition and hydrogen bromide elimination, 1,2-dibenzoylbenzene is formed and recyclized with zinc acetic acid to the final product 1,3-diphenylisobenzofuran.[12] A publication from 1940 describes high yields for the individual stages of the extensive reaction sequence.[13]
The (much cheaper) phthaloyl chloride gives also access to 1,2-dibenzoylbenzene via Friedel-Crafts acylation with benzene,[14] which is reduced to 1,3-diphenylisobenzofuran in 78% yield using potassium borohydride.[15]
The synthesis of 1,3-diarylisobenzofurans from 2-acylbenzaldehydes and boronic acids is less cumbersome and gives better yields,[16]
just like the synthesis from salicylaldehydes via phenacylhydrazones, which undergo oxidation with lead(IV) acetate to give ortho-diketones,[17] followed by the reaction with an aryl Grignard reagent.[18]
Properties
1,3-Diphenylisobenzofuran is a yellow, light- and air-sensitive, crystalline solid that is soluble in many organic solvents with a maximum absorption around 420 nm (in solution), which generates intense fluorescence.[19] Fluorescence measurements can be performed in DMF and DMSO because of the stability of 1,3-DPBF in those solvents. In chloroform and carbon tetrachloride the dissolved 1,3-diphenylisobenzofuran is rapidly photolyzed by attack of CHCl2 and CCl3 radicals, even in the absence of oxygen.[20] [24 ]
With ethanol, 1,3-diphenylisobenzofuran forms an orange-yellow, fluorescent solution. On irradiation, it forms a colorless photodimer (upon with exclusion of oxygen), upon discolouration of the solution.[21]
The compound's refractive index is 1,6700 at 25 °C and 589 nm.[22]
Use
Reagent for determination of singlet oxygen
In the presence of methylene blue irradiated with red laser light, 1,3-diphenylisobenzofuran reacts with intermediate singlet oxygen 1O2, forming an unstable peroxide that decomposes into (colorless) 1,2-dibenzoylbenzene.[24] The detection of singlet oxygen by 1,3-diphenylisobenzofuran is based on this reaction, even in biological systems. For biological systems, water-soluble derivatives of 1,3-diphenylisobenzofuran were developed.[25] The singlet oxygen generation of photosensitizers were monitored by photolysis of 1,3-diphenylisobenzofuran (DPBF). 1,2-Dibenzoylbenzene absorbs at <300 nm, therefore making DPBF an optimal chemical trap for detecting singlet oxygen, as most photosensitizers absorb <400-600 nm. This allows for an accurate determination of the photodegradation of the molecule.
Dienophile in Diels-Alder reactions
Isobenzofurans like 1,3-diphenylisobenzofuran are among the most reactive Diels-Alder dienes known to date,[26] and are useful for scavenging short-lived and unstable olefins and alkynes. The group led by Georg Wittig made important contributions to this topic.
With the unstable cyclohexyne, 1,3-diphenylisobenzofuran reacts to a tricyclic compound that gives a 9,10-diphenylcyclohexenonaphthalene after hydrogenation and hydrogen abstraction.[27]
1,3-Diphenylisobenzofuran gives similarly with benzyne (dehydrobenzene) an oxygen-bridged anthracene (in 85% yield), which can be reduced with zinc to 9,10-diphenylanthracene (88% yield).[28]
Cyclopropenone (which is unstable above its melting point of -29 °C) reacts quantitatively at room temperature with 1,3-diphenylisobenzofuran to form a Diels-Alder adduct,[29] which is exclusively an exo isomer.[30]
Dimethyl acetylenedicarboxylate reacts with 1,3-diphenylisobenzofuran as dienophile in 84% yield to yield the corresponding adduct.[31]
1,3-Diphenylisobenzofuran reacts also with heterocyclic dienophiles such as 3-sulfolene to the corresponding Diels-Alder adduct.[32]
Molecular building block for polyaromatics
Polyaromatic hydrocarbons (PAHs) are of interest as precursors to graphite but also raise concern as ingredients of pollution. They have persistence and carcinogenicity. 1,3-diphenylisobenzofuran reacts quantitatively with acenaphthylene when heated to 160 °C to give 7,12-diphenylbenzo[k]fluoranthene.[33]
The twice occurring Diels-Alder reaction of 1,3-diphenylisobenzofuran with p-benzoquinone yields almost quantitatively a product that can be reacted further with p-toluenesulfonic acid to give a pentacene derivative in 49% yield.[34]
Literature
References
- ↑ Шаблон:Citation
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- ↑ A. Guyot, J. Catel, Bull. Soc. Chim. France, [3] (35), 1124 (1906)
- ↑ A. Guyot, J. Catel, Compt. Rend. Hebd. Acad. Sci., Ser. C140, 1348 (1905)
- ↑ Шаблон:Citation
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