Photocycloaddition anhydrides

Similar products have been isolated from the photocycloaddition of dimethyl-maleic anhydride to isoprene.(97>... 

Photocycloadditions of maleic anhydride and dimethylmaleic anhydride to various other substituted cyclohexadienes and to cycloheptatriene have also been reported/58,97 98 ... 

The photocycloaddition of maleic anhydride to cyclohexene has been found to occur through ground state complexes of charge-transfer type<99> ... 

The photocycloaddition of dimethyl maleate to norbomene yields cyclobutanes (91) and (92), while the photocycloaddition of maleic anhydride to this olefin yields (92) and (93) (after hydrolysis)<100> ... 

The photocycloaddition of maleic anhydride to acenaphthylene has been studied by Hartmann and Heine.(107a> Irradiation of acenaphthylene in the presence of maleic anhydride in light-atom solvents (dioxane, acetone, or acetonitrile) yields only dimers or copolymers of acenaphthylene. In heavy-atom solvents (dichloromethane, dibromomethane, or iodomethane), however, dimerization is suppressed and cycloaddition with maleic anhydride predominates ... 

The thermal Diels-Alder reactions of anthracene with electron-poor olefinic acceptors such as tetracyanoethylene, maleic anhydride, maleimides, etc. have been studied extensively. It is noteworthy that these reactions are often accelerated in the presence of light. Since photoinduced [4 + 2] cycloadditions are symmetry-forbidden according to the Woodward-Hoffman rules, an electron-transfer mechanism has been suggested to reconcile experiment and theory.212 For example, photocycloaddition of anthracene to maleic anhydride and various maleimides occurs in high yield (> 90%) under conditions in which the thermal reaction is completely suppressed (equation 75). 

Acetone-sensitized [2+2]-photocycloaddition of 2(3//)-oxazolones 247a to maleic anhydride and dimethylmaleic anhydride gives the corresponding anti-cyclobutane cycloadducts 253 as the major products. Similar photoreaction of 2(37/)-oxazolones with 1,6-anhydro-4-(9-benzyl-2,3-dideoxy- 3-D-e 7t/ira-2-hex-enopyranose 254 results in the exclusive formation of the anh-cyclobutane-type adduct 255 (Fig. 5.61). ... 

Dialkyl ketones can undergo radiative deactivation (fluorescence) from the singlet in solution. For example, the quantum yield of fluorescence of acetone at 25°C is 0.01.30 However, the addition of maleic anhydride quenches this fluorescence, and the photocycloaddition product is obtained. Thus, it appears that, in this case, the photocycloaddition reaction can compete with fluorescence for the n,n singlet.32 Such is not the case with ordinary olefins. For example, the fluorescence of acetone was completely unaffected by the addition of 2-pentene,30 and the photocycloaddition reaction is inefficient.32... 

The ,ir singlet may not be quenched to the same extent as the triplet. For some carbonyl compounds, as with acetone with maleic anhydride, where the rate of photocycloaddition is fast enough to compete with intersystem crossing, this state may play an important... 

Other five-membered heterocyclic enones used in [2 + 2] photocycloadditions are 1//-pyrrole-2,3-diones86-88 and derivatives of maleic anhydride. Some cycloadducts of dimethylmaleic anhydride and unsaturated acid esters have been used as monomers for condensation polymers.89... 

Thiophene on irradiation in presence of dihalogenomaleimides leads to low yields of the 2-substituted products (Scheme 89) (78TL125). When benzo[6]thiophene is irradiated in the presence of dibromomaleic anhydride, both photosubstitution and photocycloaddition are observed (Scheme 90) (77BCJ1797). The ratio of photosubstitution relative to cycloaddition increases with the temperature and polarity of the solvent. A common triplet exciplex has been suggested for both processes. 

The photocycloaddition of aliphatic ketones to the electron-deficient double bonds of frans-l,2-dicyanoethylene282,283 and maleic anhydride 282 [Eq. (72)] is believed to proceed by an alternative mechanism involving nucleophilic attack on the double bond by the n, ir singlet state of the carbonyl,... 

New examples of [n2 +, 2] photocycloaddition of maleic anhydride (318) to alkenes have been reported.262 The major product of addition to ketene (319), for example, is the spiro cyclobutane (320).263 The stereoselective addition of dichlorovinylene carbonate to phenanthrene has been described,264 and the photoaddition of this carbonate (321) to the alkene (322)... 

Ortho photocycloaddition was first reported in a U.S. patent [1] dated September 3, 1957. Irradiation of benzonitrile in the presence of various alkenes resulted in the formation of derivatives of l-cyanobicyclo[4.2.0]octa-2,4-diene. The first ortho photocycloaddition to benzene was reported in 1959 by Angus and Bryce-Smith [2], who discovered that benzene and maleic anhydride react to form a stable adduct at 60°C under the influence of ultraviolet radiation. This 1 2 adduct was formed from one molecule of benzene and two molecules of maleic anhydride. Two years later, Bryce-Smith and Lodge [3] found that acetylenes could also be photoadded to benzene. The isolated products were cyclooctatetraenes, formed by ring opening of the primarily formed bicyclo[4.2.0]octa-2,4,7-trienes. Since those early years, hundreds of examples of ortho photocycloadditions of alkenes to the benzene ring and many mechanistic investigations have been reported and they will be discussed in this chapter. 

Ortho photocycloadditions proceeding via excitation of a ground-state charge-transfer complex have been reported for the combination of benzene and alkyl-benzenes with maleic anhydride. The reaction was discovered by Angus and... 

From the stereochemical structure of the adduct it can be inferred that the initial ortho photocycloaddition occurs with exo stereochemistry, whereas the subsequent Diels-Alder reaction of the ortho adduct with a second molecule of maleic anhydride proceeds with endo stereochemistry. 

Ortho photocycloadditions of benzene derivatives to maleic anhydride have been tabulated in Table 1. Only the structures of the primary ortho adducts are given, but these are not the isolated adducts They always undergo endo [2 + 4] cycloaddition with maleic anhydride, yielding 1 2 adducts. An interesting feature to be seen from Table 1 is that substituents on the benzene (alkyl, phenyl, or halogen) always turn up at the position most remote from the site of addition. In view of the different nature of these substituents, it seems that steric rather than electronic factors are responsible for this regioselectivity. 

Table 1 Ortho Photocycloaddition of Arenes to Maleic Anhydrides...

Askani, and Owsley and Bloomfield" have previously reported that the anhydride (261) undergoes photocycloaddition to afford [2 + 2] adducts with but-2-yne and ethene. Niniry et a/. " have now shown that (261) also dimerizes on irradiation in acetone or chloroform to give (262). The dimeriza-... 

Dimethylmaleic anhydride undergoes benzophenone-sensitized photocycloaddition to benzo[b]selenophene in benzene solution to give (70), and under comparable conditions the selenophthenes (71) and (72) give 1 1 and 2 1 [e.g., (73) and (74)] adducts.Neckers and co-workers have contributed many... 

The sensitized photocycloaddition of maleic anhydride derivatives to thiophenes to give the exo adducts (76) has been known for... 

The photocycloaddition mechanism, and consequently the reaction selectivity, may vary considerably depending on the structure of the initial material and reaction conditions. In general, an excited arene and a ground-state alkene may react with initial polarization to form an exciplex.802 In [2 + 2] photocycloaddition reactions, biradical intermediates are often involved (Scheme 6.80a), although excitation of a ground-state charge-transfer (CT) complex (Section 2.2.3) has also been discussed in some cases, such as the [2 + 2] photocycloaddition of benzene with maleic anhydride (Scheme 6.80b).817 Here a zwitterion intermediate 194 collapses to the adduct 195 only in the absence of an acid. 

Die Photocycloaddition von Maleinsaure-anhydrid mit Halogen-olefinen ermoglicht nachtriigliche Einfuhrung von Doppelbindungen zu Cyclobuten-dicarbonsauren. So wird dui oh Umsetzung mit 2-Chlor-propen 3-Chlor-3-me.thyl-cyclobutan-l,2-dicarbonsaure-anhydrid (29% d.Th. F 81,5-83°) und hieraus mit Kaliumhydroxid l-Methyl-2,3-di-carboxy-cyclobuten (F 189-191°) zuganglich4. 

The photoaddition of diketene to the anhydrides (366) yields the [2 + 2] adducts (367) and (368). A study of the photocycloaddition of cyclohexene to maleic anhydride sensitized by an insoluble benzoylated polystyrene has shown that the technique is nearly as efficient as the use of free benzophenone. The cycloadducts (369) and (370) are obtained from the acetone-sensitized addition of 3,3-dimethylbut-l-yne to the anhydride (371). The product (372) is also found in the reaction mixture. This material is light sensitive and is converted by... 

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