Photocyclization intramolecular

Corchnoy, S.B. et al.. Intramolecular proton transfers and structural changes during the photocycle of the LOV2 domain of phototropin, J. Biol. Chem., 278, 724, 2003. 

The photocyclization reaction is in contrast to the photodimerization of 58 in 59. In the case of 61, the photodimerization of 58 is probably prevented by steric hindrance. It is almost certain that one optical conformer of 58 is included in 61, but a real proof of this fact requires an X-ray structural study in the future. However, the formation of the optically active 62 is valuable, because photoreaction of 58 in solution does not give any intramolecular photocyclization product34). 

Full details of the [3 + 2] photoaddition of nitrobenzene (296) to cyclohexene (297) to give the 1,3,2-dioxazole (298), stable at -70°C, have now been published.244 An analogous intramolecular cycloaddition has been proposed to account for the novel photocyclization of the nitrouracil 299 to the triazole 300 and the pathway is outlined in Scheme 9.245 A 2-azaallyt radical has been shown to be an intermediate in the photoaddition of benzo-... 

Norrish Type II photocyclizations have been employed in many instances in the synthesis of nitrogen heterocycles. Type II cyclizations are the result of an intramolecular hydrogen abstraction by an excited carbonyl group followed by cyclization of the resulting biradical. Hydrogen abstraction from the y-carbon atom is normally preferred. The introduction of a nitrogen atom... 

The intramolecular photoelimination of HC1 from JV-chloroacetyl derivatives of suitable amines is a useful and versatile approach to the synthesis of azaheterocycles. The iV-chloroacetyl derivative 357 has been converted in this way to 7-oxodesethylcatharanthine (358) in 55% yield.300 Investigations in this area have been particularly concerned with the A-chloroacetyl derivatives of benzylamines and phenethylamines the N-chloroacetyl-benzylamine 359 on irradiation affords the two 3-oxo-l,2,3,4-tetrahydroiso-quinolines 360 and 361.301 Competing photocyclizations have been observed in the case of l-[3-(chloroacetylamino)propyl]-3-methylindole (362) which is converted into three photoproducts, 363, 364, and 365.302... 

Intramolecular amine addition to benzene has been reported in the phenyl-alkylamines 368 to give the meta adducts 369 in low yield,306 whereas the [co-(anilino)alkoxy]nitrobenzenes 370 undergo photocyclization in acetonitrile to give heterocycles 371.307... 

Nitro compounds have also been reported to undergo photocyclizations. The intermediacy of an isoxazoline in the photorearrangement of o-nitro-benzaldehyde to o-nitrosobenzoic acid is now in doubt,318 but intramolecular hydrogen abstraction by an excited nitro group in nitrobenzene derivatives can result in the formation of heterocycles. 4-tm-Butyl-3-methoxy-2,6-dinitrotoluene (384) on irradiation in methanolic sodium hydroxide solution... 

Another interesting example of a photochemi-cally induced domino process is the combination of the photocyclization of aryl vinyl sulfides with an intramolecular addition as described by Dittami et al. [901 as intermediate a thiocarbonyl ylide can be assumed. The domino-Norrish I-Knoevenagel-allyl-silane cyclization developed by us allows the efficient stereoselective formation of 1,2-trans-subsituted five- and six-membered carbocycles.1911 A photochemical cycloaddition of enamino-aldehydes and enamino-ketones with the intermediate formation of an iminium salt followed by addition to allylsilanes gives access to novel bicyclic heterocy-des. New examples of photochemically induced... 

The light-induced yellowing of musk ambrette 48 is simulated41 by photolysis of 48 in 0.1 N methanolic sodium hydroxide solution to give the azobenzene 50 (through the intermediacy of azoxybenzene) and by-products 51 and 52, by intramolecular photocyclization (equation 36). 

The direct photocyclization of another interesting acceptor-donor pair, the amine-enone system, has been reported by Mariano [224-226]. Direct irradiation of -(aminoethyl)cyclohexenones 281 leads to the excitation of the conjugated cyclohexenone chromophore. Intramolecular single-electron transfer from the amine donor to the cyclohexenone excited state results in the formation... 

Further research on intramolecular photocyclization of amino enones and amino ketones based on electron transfer has been made by Kraus and Chen [228]. In analogy to the earlier results of Roth and El Raie [229], Kraus and Chen obtain the cyclopropanol derivative 286 as single stereoisomer by direct irradiation of 285. Photolysis of the amino enone 287 does not lead to a three-membered ring product, but only to pyrrolidine 288. The irradiation of the unsaturated keto ester 289 results in the even more unexpected formation of a nine-membered ring product 290. Such remote photocyclizations have rarely been described so far. 

The photochemistry of imides, especially of the N-substituted phthalimides, has been studied intensively by several research groups during the last two decades [233-235]. It has been shown that the determining step in inter- and intramolecular photoreactions of phthalimides with various electron donors is the electron transfer process. In terms of a rapid proton transfer from the intermediate radical cation to the phthalimide moieties the photocyclization can also be rationalized via a charge transfer complex in the excited state. 

From the foregoing discussion, it is clear that DPM rearrangements are very general for a variety of 1,4-unsaturated systems, such as, 1,4-dienes, (3,7-unsaturated aldehydes and ketones, and different 1-aza-1,4-diene derivatives. Surprisingly, the literature was devoid of studies describing the photoreactivity of the closely related 2-aza-1,4-diene derivatives. For many years, the only studies in this area were carried out by Mariano and his co-workers [60] on the photochemistry of iminium salts derived from 2-aza-1,4-dienes. The results obtained demonstrated the synthetic utility of the photocyclizations of iminium salts to different heterocycles, in reactions that are initiated by intramolecular single electron transfer [60]. 

Scheme 44 Tandem intramolecular photocyclization of 2-(l-naphthyl)ethyl w-aniU-noaUcanoate.

This minor product has been now isolated and converted into the corresponding pentacyclo[5.3.0.0 .0 .0 ]decanedicarboxylic acid via intramolecular [2 - - 2] photocyclization. The material thereby obtained was converted into the corresponding cage di(p-nitrobenzyl ester) derivative via the method shown in Scheme 12. The structure of the resulting diester was established unequivocally as 40 via application of X-ray crystallographic methods (see Fig. 3.2) [28]. 

Heck reaction, intramolecular, 60, 2 Helicenes, synthesis by photocyclization, 30, 1... 

The earliest pioneering work, due to Georgian and Saltzman began with Robinson annulation of 436 and intramolecular [2+2] photocyclization of the bicyclic enone. 

Hosomi H, Ohba S, Tanaka K, Toda F (2000) The first in situ observation of intramolecular rotation and cyclization of anilide by an X-ray study partial single-crystal to single-crystal photocyclization of A-methyl-A- ( )-methylmethacrolyl anilide in inclusion crystals. J Am Chem Soc 122 1818-1819... 

An intramolecular photocyclization approach has been developed for the synthesis of strained tetrahydrofuran and tetrahydropyrrole derivatives from tetronates (Table 1) <2004EJO4582, 2005JOC9798>. The cycloaddition reaction is not sensitive toward the degree of substitution on either reactive center and produces a single diastereoisomer in all cases (Equation 42). 

An intramolecular photocyclization catalyzed by copper(I) triflate provided a key step in a total synthesis of the ginseng sesquiterpenes a- and /J-panasinsene, (8) and (9). The unsaturated allylic alcohol (6) is cyclized by irradiation at 254 tun in the presence of CuOTf to a mixture of saturated alcohols, which is oxidized to the ketone 7. The ketone is inert to methylenetriphenylphosphorane, but can be converted into a 2 5 mixture of 8 and 9 by addition of mcthyllithium followed by dehydration.2... 

Nonconjugated dienes and polyenes have triplet photochemistry which may be considered to arise from intramolecular interaction of one excited double bond with an isolated ground-state double bond. For example, the photocyclization of enrfo-dicyclopentadiene can be effected using acetone as a sensitizer.286 Other more flexible 1,5-dienes, when sensitized to triplet states, cross couple to yield bicyclo[2.1.1]-hexane structures. For instance, triplet mercury atoms convert both 1,5-hexadiene and 1,5-cyclooctadiene to such structures.267 Irradiation of the cyclooctadiene in the presence of cuprous chloride produces the tricyclo derivative in good yield266 but recent evidence again indicates that this latter reaction may proceed via free-radical intermediates.269... 

The photocyclization of carvone, 36, to carvonecamphor, 37, is a good example of intramolecular cycloaddition of an enone to an isolated double bond422 ... 

If biradical species are intermediates in these intramolecular cyclizations, products which represent radical-radical disproportionation should appear occasionally. The photocyclization of citral423 probably is a fitting example. 

Citral (Formula 210) undergoes an intramolecular photocyclization to (Formula 211) which is not of the type usually encountered (see Sec. IIE)... 

Synthesis of the dibenzofuran (27) by irradiation of grisa-3, 5 -diene-2, 3 -dione (28) is believed to involve electrocyclic ring opening followed by intramolecular cycloaddition to the ketene and elimination of carbon dioxide, as shown in Scheme 2.24 Analogous photocyclizations are responsible for the photochromism exhibited by heterocyclic fulgides such as ( )-a-3-furyl-ethy idene(isopropylidene)succinic anhydride (29), which on irradiation... 

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