Amines, photoaddition reactions

Since it has been observed that the hydrogen atoms attached to nitrogen in amines were not easily abstractable in free radical reactions (6, 74), it may be assumed that the aldehydic part of the formamide molecule will be more reactive in the photoaddition reactions than the amino function, thus leading to the following addition reaction with terminal olefins,... 

Lewis and his coworkers reported the intramolecular photoaddition of aliphatic secondary amines to arylalkenes to give 5- and 6- membered cyclic amines (Scheme 17) [66-67]. Ohashi reported that the other type of photoaddition reaction takes place when 1,4-dicyanobenzene and triethylamine are used as substrates. This photoreaction can be explained in terms of the deamination of the initially produced diethylaminoethylated compound (Scheme 18) [68]. 

The synthetic and mechanistic aspects of photoaddition reactions of amines with excited states of arenes and aryl olefins have been extensively investigated [10-12, 277],... 

Intramolecular photoaddition reactions of secondary amines linked to styrenes can result in the formation of C-N bonds at the a- or / -carbon (Scheme 54) [288-290], The product yields and the ratio of the two products are shown in Table 11. 

Intramolecular photoaddition reactions of amines for the construction of A -heterocycles has also been successfully explored by Sugimoto and coworkers (Scheme 57) [296-302]. 

Topics of relevance to the content of this chapter which have been reviewed during the year include photoactive [2]rotaxanes and [2]catenanes, photochemical synthesis of macrocycles, phototransformations of phthalimido amino acids, photoaddition reactions of amines with aryl alkenes and arenes, photoreactions between arenenitriles and benzylic donors, photostability of drugs, polycyclic heterocycles from aryl- and heteroaryl-2-propenoic acids, photoreactions of pyrroles, photoamination reactions in heterocyclic synthesis, switching of chirality by light, photochromic diarylethenes for molecular photoionics and solid state bimolecular photoreactions. 

The initial report of intramolecular benzene-tertiary amine addition by Bryce-Smith et al. might have been expected to trigger a flurry of research activity similar to that generated by intramolecular benzene-olefin photoaddition reactions. However. a detailed account of the formation of adducts 3 and 4, including isolated yields and complete structural characterization, never appeared. Neither have additional examples of arene-tertiary amine addition reactions been reported. 

PHOTOADDITION REACTIONS OF AMINES WITH ARYL OLEFINS AND ARENES Frederick D. Lewis... 

The second one is the synthesis of a lactoside glycodendron where the photoaddition is combined with a reductive amination. This latter occurs between an amine and an aldehyde to form an imine that is reduced into the corresponding open chain amine. This reaction has the great advantage to not require extensive use of protecting groups (Scheme 9). 

Kim KM, Park HJ, Kim JN, Yoo HJ, Yoon UC (2013) Photoaddition reactions of fullerene C60 with alpha-silyl tert-amines leading to new fullerene derivatives. In ref [18], 523... 

Investigations of phthalimide photochemistry in the authors laboratories have concentrated on SET-induced excited-state reactions with a-trialkylsilyl substituted ethers, thioethers, and amines. These efforts have uncovered several interesting photochemical reactions. For example, in an early effort simple, a-silyl-substituted ethers, thioethers, and amines were observed to undergo efficient photoaddition reactions with phthalimide and its N-methyl derivative (Scheme 5.4) [20]. In these processes, thermodynamically/kinetically driven SET from the a-silyl donors 13 to excited phthalimide leads to formation of ion radical pairs 16 (Scheme 5.5). Solvent (MeOH) promoted desilylation of the cation radicals 16 and protonation of the phthalimide anion radicals 15 then provides radical pairs 17, the direct precursor of adduct 14. 

Lewis, F.D., Photoaddition reactions of amines with aryl olefins and arenes, in Advances in Electron Transfer Chemistry, Vol. 5, Mariano, P.S., Ed., JAl Press Inc., Greenwich, CT, 1996, p. 1. 

Kanaoka, Y, Sakai, K., Murata, R., and Hatanaka, Y, Photoaddition reactions of N-methylphthal-imide with toluenes and amines. Heterocycles, 3, 719, 1975. 

Ohmiya, S., Noguchi, M., Chen, C.Y., Murakoshi, 1., and Otomasu, H., Intermolecular photoaddition reaction of ahphatic tert-amines to N-alkyl-2-pyridones, Chem. Pharm. Bull, 37,2516-2518, 1989. 

Primary and secondary amines can add to Cjq as nucleophiles (Section 3.3). Tertiary amines can not form similar addition products, rather an electron transfer imder formation of zwitterions is often observed (Section 3.3). However, a photochemical reaction of tertiary amines with Cjq is possible and leads to complex mixtures of addition products [52-62]. The product distribution strongly depends on conditions such as temperature and the presence of either light or oxygen. If oxygen is thoroughly excluded, 9 is the major product (Figrue 6.8) in the photoaddition of triethylamine [56, 59]. It can be isolated in low yields. 

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. 

Photoadditions that arise by initial excitation of the aromatic compound are not common. Benzvalenes are readily attacked by hydroxylic compounds, and so irradiation of benzene in aqueous solutions of acetic acid, for example, results in the formation of a bicydic product (and an isomer derived from it by subsequent photoisomerizationl as a result of addition to the initially formed valence isomer (3.38). A different kind of photoaddition occurs when benzenes react photochemically with amines cyclohexa-T, 4-dienes are the major products (3.39), accompanied by cyclohexa-1.3-dienes, and unlike many of the photochemical reactions of benzene this does not suffer loss of efficiency in scaling-up. 

For the reactions described so far in this section, the ketone substrates have lowest excited states that are (n.ii ) in character aliphatic ketones may react by way of the singlet or the triplet state, and aryl ketones normally through the triplet because intersystem crossing is very efficient. The efficiency of photochemical hydrogen abstraction from compounds such as alcohols or ethers is very much lower if the ketone has a lowest (Ji,n triplet state, as does I - or 2-acetylnaphthalene (CmH-COMe). However, all aryl ketones, regardless of whether their lowest triplet state is fn,Jt l or (Jt.Ji ), react photochemically with amines to give photoreduction or photoaddition products. A different mechanism operates (4.38), that begins... 

A study of the photoaddition of formamide to olefins was undertaken with the aim of finding a new process for converting olefins to higher amides and possibly further to amines by reduction or by the use of the Hofmann rearrangement. Since hydrolysis of the amides to the corresponding carboxylic acids can be effected by standard procedures, this reaction provides a new process for carboxylation of olefins under mild conditions at room temperature. A similar reaction has been shown to take place in a thermal process, using peroxides as initiators (60). 

Since alcohols are less effective as hydrogen donors than amines, a PET photoaddition can occur only when the oxidized component of the reaction is the alkene. Furthermore, if the photosensitizer is chiral, the polar addition would occur in an enantiodifferentiating manner to some degree. Thus, the photoaddition of 2-propanol to 1,1-diphenylpropene, when sensitized by chiral naphthalene(di)carbox-ylates, formed the anti-Markovnikov photoadduct with enantiomeric excesses of up to 58% [53]. Unfortunately, the reaction is far from attracting synthetic interest as the yields are still too low. 

Hasegawa, E., Xu, W., Mariano, P.S., Yoon, U.-C., and Kim, J.-U. (1988) Electron-transfer-induced photoadditions of the silyl amine EtjNCHjTMS to a,p-unsaturated cyclohexenones. Dual reaction pathways based on ion-pair-selective cation-radical chemistry. Journal of the American Chemical Society, 110, 8099-8111. 

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