Subject photocyclization

This type of one-pot reaction represents a simple method for the synthesis of a large variety of cyclic OPV oligomers of different sizes and composed of different arylene building blocks, such as phenylene, biphenyl-diyl and naphthylene. The compounds are suitable subjects for the study of photoinduced Z/ -isome-risation and photocyclization. 

The photocyclization of enamides has been the subject of detailed study and provides a valuable approach to the synthesis of alkaloids. A comprehensive review has been published.31 A variety of reaction types has been reported. The N-benzoylenamine 33, for example, is converted on irradiation to the trans-lactam 34 by a process involving conrotatory photocyclization followed by a thermally allowed [l,5]-suprafacial hydrogen migration.32 The influence of substituents on this transformation has been studied.33 The enacylamine 35 undergoes an analogous cyclization to give a mixture of cis- and trans-lactams 36, the ratio of which is solvent... 

N-Chloroacetylbenzylamines (43) were subjected to photocyclization by Japanese researchers (Scheme 10). In these examples, the aromatic ring has one or more hydroxy substituents (74TL1181 77H251, 77T489 81CPB128). Some chloroacetyl derivatives could be cyclized in the presence of ZnCfe (87S637). 

Baylis-Hillman adducts such as 55 and 56 derived from 2-nitrobenzaldehydes were shown to function as useful precursors to functionalized (1H)-quinol-2-ones and quinolines. Treatment of 55 and 56 with iron and acetic acid at 110 °C afforded 57 and 58, respectively <02T3693>. A variety of other cyclization reactions utilized in the preparation of the quinoline scaffold were also reported. An iridium-catalyzed oxidative cyclization of 3-(2-aminophenyl)propanols afforded 1,2,3,4-tetrahydroquinolines <02OL2691>. The intramolecular cyclization of aryl radicals to prepare pyrrolo[3,2-c]quinolines was studied <02T1453>. Additionally, photocyclization reactions of /rans-o-aminocinnamoyl derivatives were reported to provide 2-quinolones and quinolines <02JHC61>. Enolizable quinone and mono- and diimide intermediates were shown to provide quinolines via a thermal 6jt-electrocyclization <02OL4265>. Quinoline derivatives were also prepared from nitrogen-tethered 2-methoxyphenols. The corresponding 2-methoxyphenols were subjected to a iodine(III)-mediated acetoxylation which was followed by an intramolecular Michael addition to afford the quinoline OAc O... 

The most widely utilized photoreaction of enamine derivatives is undoubtedly the photocyclization of enamides. Since this subject has already been extensively reviewed3 only a brief discussion is presented here. 

Miscellaiieoiis Additions.—Aoyama and his co-workershave reported the synthesis of p-lactams (115) by photocyclization of the methacrylamides (116). Photocyclization of the azetidinones (117) affording the penicillin derivatives (118) has been the subject of a patent application. ... 

The photocyclization reaction of 2-allylanilines, depending on the degree of alkylation at the N atom, has long been a subject of interest. When iV,iV-dialkylanilines 60a-62a were irradiated in methanol, the corresponding 2-cyclopropylanilines 60b-62b were formed in 73, 60 and 47% yield, respectively (equation 17)163. This reaction proceeds in the triplet state via a clean aromatic di-jr -methane rearrangement. However, no reaction occurs when 2-allyl-l-(Ai,Ai-dimethylamino)naphthalene is irradiated in methanol. Thus, this photochemical cyclopropanization of allylated anilines appears to have only a limited scope as preparative method, because it is successful only for a few substrates. 

As can be seen from the foregoing, phthalimide photocyclizations have provided useful synthetic routes to a variety of heterocyclic products. Machida et al. have used the reaction to yield the spiro compounds (325) from the irradiation (in methanol) of the phthalimide derivatives (326). The products are presumed to be formed via bond formation in the biradical produced by the addition of methanol to the radical cation/r ulical anion pair. The indoles (327) undergo photochemical (2-f-2)-addition with A methyl phthalimide to afford the oxetan adducts (328). This work has also been the subject of a patent application. " ... 

Photochromism including 1,2-diarylethenes is a quite interesting subject and so many reviews and original papers have appeared in these two years. The intramolecular photocyclization of 1,2-diaryethenes is the most typical photochromic system. A variety of 1,2-diarylethenes were synthesized and characterized based on the photochemical and physical, thermochemical, and electrochemical properties. Their fluorescence behaviors were also characterized. Irie et al. have developed the photochromism of crystalline states having blue, yellow, and red color depending on substituents. ... 

The photochemical mechanism of the BP-containing PI was discussed, but it is not still well understood. Scaiano et al. [175] were the earliest to study the photochemical mechanisms of a model compound in solution using conventional and laser time-resolved techniques. In particular, it is important to learn whether the benzophenonediimide behaves as BP or as N-arylphthalimides. They used a model prepared from BTDA and 2-isopropylaniline. This model compound might be subjected to intramolecular photocyclization at the imide carbonyls as reported in the literature [162]. But no... 

The intramolecular addition reactions of aminoalkylstyrenes have proven to be a particularly fruitful subject of investigation. Photocyclization reactions of the N,N-diethyl a-aminoaUcylstyrenes 9 and 10 yield the pyrrolidine 9a and piperidine 10a, respectively (Scheme 10), as mixtures of diastereoisomers. > ° Similarly, the cyclic amines 11 and 12 yield the bicyclic adducts 11a and 12a, respectively (presumably as mixtures of diastereoisomers), in good preparative yield. These reactions are assumed to occur via... 

The aminocyclopentene products of these pyridinium salt photoreactions were shown to arise by acid-catalyzed methanolytic aziridine ring opening of bicycHc aziridine intermediates. Accordingly, treatment of the bicyclic aziridines 24 and 25, produced by irradiation of basic MeOH solutions of the salts 20 and 21, with catalytic quantities of HCIO4 in MeOH led to smooth formation of the respective aminocydo-pentenes 22 and 23. Thus, when base is not included in pyridinium salt photoreaction mixtures, the initially formed photocyclization products are N-protonated bicycHc aziridines, which are subject to nucleophile-induced cleavage at their allylic aziridine centers. 

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