Photoaddition of maleic anhydride

Photoaddition of acetylene, 349 Photoaddition of allene, 349 Photoaddition of dichloroethylene, 349 Photoaddition of ethylene, 348 Photoaddition of hexafluoroacetone, 345 Photoaddition of maleic anhydride, 348 Photochemical addition of ethylenes and acetylenes to steroidal enones and dienones, 343... 

As in the photoaddition of maleic anhydride to norbomene, the endo product (93) may arise from a charge-transfer complex. 

The stereospecificity of the photoaddition of maleic anhydride to cyclohexene can be conveniently rationalized as follows ... 

The photoadditions of maleic anhydride to some other compounds are as follows(38a 105 108) ... 

Schenck has shown that the photodimerizations of various substituted maleic anhydrides proceed via triplet states.259 The photoaddition of maleic anhydride to benzene439 is now known to involve excited states of maleic anhydride-benzene complexes.440 The preferred mechanism for the reaction in the presence of high-energy sensitizers is shown at the top of page 125. 

Bryce Smith, D., Deshpande, R. R., Gilbert, A., Mechanism of Photoaddition of Maleic Anhydride to Benzene, Tetrahedron Lett. 1975, 1627 1630. 

A new route to pleiadienes involves photoaddition of maleic anhydride derivatives to acenaphthene, oxidative removal of the anhydride groups, and ring-opening of the resulting cyclobutenes (Scheme 18). Schmidt has reported further details of the synthesis of optically active tricarbonyl(cyclobutadiene)iron complexes, the first step involving [2 + 2] addition of 1,2-dichloroethylene to dichloromaleic anhydride. 

The initial adduct (356) of photoaddition of maleic anhydride to benzene cannot be isolated because of the reactivity of the diene function, although it may be trapped by a variety of dienophiles. Further evidence has now been provided for its formation, especially by an independent synthesis and examination of its photochemical be-... 

Table 6.3. Relative Rates of 2 1 Photoaddition of Maleic Anhydride to Some Aromatic Compounds at 30°C, Unsensitized, and Sensitized by Benzophenone"...

The prototype of the present surface photografting is the surface photoreaction of maleic anhydride(MAH) onto poly(butadiene) film(15). Although fair improvement of surface wettability was achieved, photoaddition of MAH cannot be applied to other polymers having no ethylenic double bonds. The present process is applicable to almost all polymers except for poly(tetrafluoroethy-lene) and its analogues. 

An example of the equivalent (photoaddition) reaction following hetero-molecular photoassociation is provided by the photochemical addition of maleic anhydride to anthracene." Livingston and coworkers100 have shown that the anthracene triplet state is not involved in this reaction and that, in terms of Eq. (47) in the appropriate form, q%. = 0.03. However, if the excited complex XMQ formed directly by light absorption in the charge-transfer band is the reactive intermediate, this produces the adduct with a computed efficiency of 347 . 

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)... 

Bryce-Smith and Gilbert have shown that toluene, t-butylbenzene, chlorobenzene, o- andp-xylene, and biphenyl all undergo photoaddition to maleic anhydride, yielding 1 2 adducts [33], All the substituents decrease the rate of formation of adducts. Benzonitrile, nitrobenzene, phenol, methyl benzoate, durene, hexamethylbenzene, naphthalene, and biphenylene fail to undergo the addition of these, benzonitrile, nitrobenzene, methyl benzoate, and biphenylene do not form charge-transfer complexes. Bradshaw [34] found that various alkylben-zenes give 1 2 adducts with maleic anhydride upon photosensitization with acetophenone. 

The present widespread interest in photoaddition reactions of aromatic compounds originates from observations made over 25 years ago that irradiation of maleic anhydride solutions in benzene produced the 2 1 adduct (33). Numerous accounts concerning the mechanism and scope of the reaction have since appeared and a kinetic model for the process has been proposed. "" The rate of reaction was found to be dependent on the concentrations of benzene, sensitizer, and oxygen but was essentially independent of temperature change in this last parameter does, however, have a pronounced effect on the distribution of 2 1 photoadduct isomers produced from maleic anhydride and methylbenzenes. Subsequent to the early findings on the maleic anhydride system several maleimides were also shown to form 2 1 adducts analogous to (33) with benzene. It is therefore most interesting that the 2 1 adduct (34) of... 

Additions to Aromatic Hydrocarbons. A variety of photochemical additions to aromatic hydrocarbons have been reported. Benzene and its derivatives add to maleic anhydride74-76 as well as to simple olefins,77-80 isoprene,81 acetylene derivatives,79,82 and alcohols.83 The mechanism of the maleic anhydride-benzene reaction is discussed in Section IV. A.4. Naphthalene forms a photoadduct with dimethyl acetylenedicarboxylate62 and with acrylonitrile8211 while anthracene behaves similarly with maleic anhydride84 and with 1,2-benzanthracene.85 The photoaddition of several aromatic amines to anthracene has been reported to proceed via a charge transfer complex86,87 in fact, the majority of these addition reactions may proceed in this manner. 

The cycloaddition of a variety of sulfur heterocycles to alkenes has also been reported. Dibromomaleic anhydride undergoes [ 2 + 2] cycloaddition to thiophen295 and to benzo[b]thiophen.296 The photoaddition of benzo-[(>]thiophen 1,1-dioxides to alkenes also affords cyclobutane derivatives.297 Of particular interest is the addition of 3-acetoxybenzo[6]thiophen (350) to cyclohexene to give the adduct (351), which on treatment with base, undergoes a retro-aldol ring opening to benzo[6]thiepinone (352).298 A mixture of stereoisomeric cyclobutane derivatives were obtained on irradiation of 2,6-diphenyl-4//-thiopyran-4-one 1,1-dioxide in cyclohexene.299 The [ 2 + 2] cycloaddition of sulfolen to maleic anhydride and to maleimide has been reported.300... 

Irradiation of mixtures of benzene and maleic anhydride in the presence of trifluoroacetic acid has shed more light on the mechanism of the photoaddition [36], Under these circumstances, formation of the 1 2 adduct is completely suppressed and a new 1 1 adduct, phenylsuccinic anhydride, is obtained. It was concluded from these experiments that excitation of the ground-state complex between benzene and maleic anhydride leads to a zwitterionic intermediate that can be intercepted by protonation (Scheme 5). 

Bryce-Smith et al. [41] therefore proposed the mechanism shown in Scheme 7 for the photoaddition of benzene to maleic anhydride. 

Scheme 7 Mechanism of the direct and the sensitized photoaddition of benzene and maleic anhydride.

Bradshaw [74] reported in 1966 that maleimide undergoes sensitized photochemical addition to benzene, producing the imide analog of the corresponding maleic anhydride photoadduct. The author observed that the reaction probably proceeds by the addition of electronically excited maleimide to benzene. The photoaddition proved successful also with toluene, /-butylbenzene, and ethylbenzene. Simultaneously, Bryce-Smith and Hems [75] reported that 2 1 photoadducts are formed from maleimide, iV-n-butyl-,. V-benzyl-, iV-o-tolyl-, and iV-2,6-xylylmaleimide with benzene.. V-Phenyl, N-p-tolyl-, and A-p-methoxyphenylmaleimide did not form photoadducts. Trifluoroacetic acid was found to be virtually without effect on the photoaddition of N-n - bulyI maleimide No phenyl-A- -butylsuccinimide was detected [36], It was concluded that a dipolar intermediate is not involved. When N-n-bulylmalcimide and benzene were irradiated in the presence of tetra-cyanoethylene, a 1 1 1 adduct was formed [37],... 

Olefinic dienophiles such as maleic anhydride and maleimide add to 4,6-dimethyl-2-pyrone to afford mono Diels-Alder adducts. These on irradiation afford, by a photo-decarboxylation, a diene which can be trapped by a dienophile to afford the products (311). - - Acetone-sensitized photoaddition of the oxazolones (312) to maleic and dimethyl maleic anhydride yields the adducts (313). - ... 

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... 

In an attempt to trap fulvene 2 by the Diels-Alder reaction with maleic anhydride, another new photoreaction was discovered/ A cycloadduct was obtained which was suggested to be formed by direct addition to the excited state of benzene. Since then, photoadditions of alkenes to benzene and substituted benzenes have been studied extensively and become a powerful tool for synthetic approaches to complex polycycHc compounds. - ... 

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