Maleic photocycloaddition with

Examples of 1,2-photocycloaddition followed by 1,4-cycloaddition are known, the reaction of maleic anhydride with aromatics being the most studied. In the case of benzene the product is... 

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... 

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. 

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. 

A (2 + 2)-photoadduct is formed on irradiation of 2,3-dimethylmaleic anhydride with 3,4-dimethyl-1-phenylphosphole. " The photocycloaddition of maleic anhydride derivatives (124) to the alkene moiety in (125) affords the adducts (126) by a straightforward (2 + 2)-addition. The (2 + 2)-photoadducts (127) are readily produced by the dimerization of the corresponding maleic anhydrides in ethyl acetate solution.The intramolecular photochemical cyclization of the succinimide derivative (128) is a key step in the new synthetic approach to the tetracyclic fragment of neotuberostemonine. ... 

Furanones, maleic anhydride, maleimides, and cyclopentenones behave similarly when irradiated in the presence of alkenes. [2-1-2]-Photocycloaddition reactions of furanones, especially y-substituted furanones with alkenes, can be highly diastereoselective. A detailed analysis of the cycloaddition of ethylene with substituted furanones gave a deep insight into the origin of the diastereoselectivity. Based on product ratio dependence on temperature and the substituents, it was proposed that a pyramidalization of the P-carbon of furanones in their relaxed excited state and a homo-anomeric effect determined the... 

---