Photocycloaddition naphthalene

Naphthalene undergoes photocycloaddition with diphenylacetylene to produce (63) and (64), with the latter thought to result through light absorption by product (63)<78) ... 

Aromatic compounds can participate in both [2+2] and [4+2] photocycloaddition reactions with uracil derivatives to give either benzocyclobutane or ethenoquinazoline (barrelene) derivatives, which can then undergo a number of subsequent photochemical reactions. The products obtained are dependent upon the reaction conditions, and thus the photocycloaddition reaction between naphthalenes 470 and l,3-dimethyl-5-fluorouracil 471 in cyclohexane gave 4a-fluoro-5,10-ethenobenzo[/]quinazolines 472 as products as a result of a [4+2] photocycloaddition (photo-Diels-Alder) reaction <2002TL3113, 2003H(61)377>. 

Table II must apply to both reactions. This has been verified by quenching the photocycloaddition of benzophenone to 2-methyl-2-butene with ferric dipivaloylmethane25 and that of benzaldehyde to cyclohexene with naphthalene.37...

The irradiation of benzaldehyde in cyclohexene solution gives rise to products of both the photocycloaddition and photoreduction reactions. Naphthalene was added to this reaction mixture in an effort to change the ratio of products, since, if the two reactions result from different excited states, that reaction involving the triplet would be quenched. The rate of product formation was slowed while the ratio of products remained unchanged therefore the photocycloaddition and photoreduction reactions involve the triplet state.37... 

Table IV summarizes the pertinent characteristics of some of the naphthyl carbonyl compounds. All of these compounds emit from a it,7T triplet very similar to that of naphthalene. Those that have been studied are resistant to photoreduction in isopropyl alcohol and photocycloaddition with 2-methyl-2-butene25 and isobutylene.17 Significant oxetane formation was, however, observed with the aldehydes, albeit with only moderate efficiency (quantum yield approximately one-tenth that of benzaldehyde).25...

Photocycloadditions of naphthalene derivatives to alkcnes have been recently reviewed.60 Examples of such reactions are the photocycloaddition of naphthalene to 2,3-dihy-drofuran,61 of 4-methoxy-l-naphthonitrile to acrylonitrile62 and of 2-trimethylsiloxynaph-thalene to methyl acrylate.63 2-Naphthols undergo cycloaddition with ethene in the presence of aluminum trihalides only.64 Other bicyclic aromatic compounds, e.g. A-acylindoles65-67 and /V-methylphenanthrene-9,10-dicarboximide,68 have also been studied in detail. Irradiation of 5/f-dibenzo[u,i7]cyclohepten-5-one (21) and dimethyl 2-methylfumarate (22) in dioxane gives the cyclobutane adduct 23 in 73% yield.69... 

The (1,4) substituted naphthalenophanes undergo [4 + 4] photocycloaddition when irradiated at X > 280 nm, in addition to fluorescence. This photoreaction is competitive with fluorescence, and requires a conformational change that can be suppressed at low temperature 93). The few reports of the lifetime or quantum yield of naphthalenophane fluorescence indicate the effects of photocycloaddition. For the anti-[2.2](1,4) isomer, kpu/ku = 0.021 in cyclohexane 93) the lifetime of syn-[3.3](l,4) naphthalenophane fluorescence was given as 15.3 ns107). Both values are low relative to the naphthalene solution excimer (kpu/kjj 0.2 xD 80 ns 71)), and this may be due in part to the photoreaction of the (1,4) naphthalenophanes. 

The N=N double bon d does take part in a few photocycloaddition reactions to give cyclic compounds with two adjacent nitrogen atoms in the ring. Intermolecular (2 + 2 cycloadditions are not known, but some intramolecular examples of this reaction are reported for quite complex compounds 15.27 in which the reacting groups are held fairly rigidly in an orientation suitable for reaction. A (4 + 2) cycloaddition takes place when naphthalene is irradiated with an electron-deficient cvdrc azo-compound (5.28). 

The photocycloaddition of cyclic and acyclic 1,3-alkadienes or furans to aromatic rings has been shown in some cases. Not only symmetrically allowed (4 + 4) photocycloaddition but also (4 + 2) photocycloaddition to benzene, naphthalene, and anthracene rings have been reported. These results are also shown in the following subsections. 

Photocycloaddition of a variety of unsaturated compounds to unsubstituted naphthalene ring has been well investigated in 1960s and 1970s the (2 + 2) cycload-... 

McCullough and co-workers first reported the photocycloaddition of acrylonitrile (33a) to naphthalene in 1970 [94,95], They systematically investigated the photocycloaddition of 33a to mono- and di-methylnaphthalenes however, the yields and selectivity were not high and usually a complex mixture was produced [128] (Scheme 18). 

Al-Jalal reported that the photocycloaddition of l-cyano-4-methoxynaph-thalene with alkenes commonly occurs at the 1,2 bonds of the naphthalene ring [126,131], However, when 2-cyano-6-methoxynaphthalene (52) was treated with 2-chloroacrylonitrile, ( )-ethoxyacrylonitrile, or ( )-cinnamonitrile, the (2 + 2) cycloadducts showed a different regiochemistry [132,133] (Scheme 21). Irradiation of 52 in the presence of ethyl vinyl ether or ( )-dichloroethene did not give a cross-adduct, but gave a photodimer of 52. 

Previously, a variety of (2 + 2) photocycloaddition of alkenes to naphthalene rings have been reported as discussed in the previous subsections. Very recently, Yokoyama and Mizuno have reported the highly regioselective and stereoselective (2 + 2) photocycloaddition between 4-substituted 1-cyanonapha-thalenes (148) and 1-substituted 3-methyl-2-butenes (149) assisted by hydrogenbonding in the ground states as shown in Scheme 48 [226],... 

Typical intramolecular (2 + 2) photocycloaddition of electron-rich alkenes to the 1-cyanonaphthalene ring via an exciplex has been reported by McCullough and Gilbert, independently. McCullough reported intramolecular photocycloaddition of bichromophoric molecules 255,258, and 259, in which the chromophores are linked by a three-atom ether chain [286,287] (Scheme 71). The fluorescence of the 1-cyanonaphthalene chromophore of 255,258, and 259 is efficiently quenched by alkenes and the typical intramolecular exciplex emissions are observed. Photocycloaddition of these 1-cyanonaphthalenes in benzene occurs at 1,2-, 3,4-, or 5,6-positions of the naphthalene ring, respectively. 

Gilbert and his co-workers reported that the photocycloaddition of 1-cyanonaphthalenes (260 and 262) gave 261 and 263, independently [288] (Scheme 72). In addition, they prepared and photoirradiated a variety of compounds that connected naphthalene and alkenes by methylene, ether, and ester tethers at various lengths [289], Among them, the reaction of 264 gave the best result, whereas the 2-substituted derivative (265) did not give any product. 

Wagner and Sakamoto reported the first example of the intramolecular (2 + 2) photocycloaddition of simple alkenes to the excited triplet state of naphthalene [290], Cyclizations of 266 and 267 are entirely triplet-state reactions The formation of cycloadducts is sensitized by Michler s ketone and is quenched by conju-... 

Prinzbach and co-workers studied the photocycloaddition of a rigid compound in which naphthalene and alkene were placed [294], Distances between naphthyl (3-carbons and olefinic carbons of 272 are 2.911 and 2.944 A. Direct or acetone-sensitized photoexcitation induced an efficient meta addition to the naphthalene ring to give 273, the ortho addition did not occur, although it is not clear whether the ortho process occurred (Scheme 76). 

Kohmoto et al. examined the photocyclization of /V-cinnamoyl- l -naph-thamides (274a-f) in benzene solution and in the solid state [295] (Scheme 77). Intramolecular (2tt + 2tt) and (2tt + 4tt) photocycloaddition of styryl group to the naphthalene ring was observed in benzene solution, whereas 275a-c were also obtained in the solid state. 

Mizuno et al. reported the site-selective photocycloaddition of 255 in the presence of Eu(III) salt [296] (Scheme 78). In the photoreaction of 255a in benzene, the cycloadduct 256a at the 1,2-position on the naphthalene ring predomi-... 

Intramolecular photocycloaddition of naphthalene and anthracene has been studied by Chandross and Schiebel [327], At concentrations above 10 3 M, bi-molecular photodimerization of the anthracene occurs in deaerated methylcyclo-hexane solution. In contrast, irradiation of much more dilute ( 2 X 105 M) solutions resulted in the formation of intramolecular adduct 342 (Scheme 94). Bouas-Laurent et al. showed that the CH2—O—CH2 link is more efficient than the (CH2)3 chain in bridging the two chromophores [328], Irradiation of diethyl ether or methylcyclohexane solution of 343 (5 X 10 5 M) with a high-pressure mercury lamp and liquid filter (X > 335 nm) gave a single photoadduct 344, which was isolated quantitatively. The quantum yield of 344 is 10 times higher than that of 342. 

Photochemical (2 + 2) and (4 + 4) photocycloaddition is well investigated and recent advances in this field easily predict the patterning of the photoreactivity. The intermolecular and intramolecular photocycloaddition of alkenes to benzene ring also has a citizenship in this field. On the other hand, most people believe the photocycloaddition of unsaturated compounds to naphthalene ring takes place at... 

However, Kubo et al. found the unusual (3 + 2) intermolecular photocycloaddition of alkenes to the naphthalene ring at the 1,8-position. The same group also reported the (3 + 2) photocycloaddition of alkenes to phenanthrene ring at the 8,9-position. 

An intriguing intramolecular (3 + 2) photocycloaddition of alkenyl methyl 1,4-naphthalenedicarboxylates has been developed by Kubo et al. [300], Intramolecular (3 + 2) photocycloaddition of alkenyl methyl 1,4-naphthalene di-carboxylates, which contain remote alkene moieties proceeded largely dependent on the chain lengths. On irradiation of benzene or acetonitrile solutions of 406a-c, no reaction was observed despite its chain length. On the other hand, in the photoreactions of 407a-e, intramolecular (3 + 2) photocycloadditions proceeded... 

Intramolecular Photocycloaddition of N—P4—A. Although the photocycloaddition of anthracene [85-100] and that of naphthalene [65-67,80-82] have been extensively studied, until recently relatively little has been reported on the cross-photocycloaddition between an anthracene and a naphthalene moiety [101-110], The main reason for this is the large difference in the quantum yields between the photocycloaddition of anthracene and the cross-photocycloaddition of anthracene and naphthalene. Thus, bichromophoric molecules with anthryl as one chromophore and naphthyl as the other generally undergo intermolecular an-thryl-anthryl cycloaddition rather than intramolecular cross-cycloaddition when irradiated. 

Mukae, H., Maeda, H., and Mizuno, K. (2006) One-step synthesis of benzotetra-and benzopentacyclic compounds through intramolecular [2 + 3] photocycloaddition of alkenes to naphthalene. Angewandte Chemie, International Edition, 45 (39), 6558-6560. 

Tsutsumi, K., Nakano, H., Furutani, A., Endou, K., Merpuge, A., Shintani, T., Morimoto, T., and Kakiuchi, K. (2004) Novel enhancement of diastereoselectivity of [2 + 2] photocycloaddition of chiral cyclohexenones to ethylene by adding naphthalenes. Journal of Organic Chemistry, 69, 785-789. 

Only few reports deal with a para photocycloaddition as the major reaction path. Recently, however, several cinnamide derivatives like 21 were efficiently transformed into the corresponding para adducts 22 (Sch. 6) [37]. Yields higher than 90% could be achieved. The para photocycloaddition is also observed with naphthalene derivatives like 1-acetylnaphthalene 23 and captodative enamino nitriles as 24 [38]. Other captodative substituted alkenes [39] as well as the fluorinated uracil derivative 26 [40] are transformed in the same way. Especially in the cases of 21 and 23, the... 

Naphthalenes also undergo 1,2-photocycloaddition with diphenylacetylene, although the products isolated are not benzocyclo-octatetraenes, but rather adducts... 

The literature of mechanistic aromatic photochemistry has produced a number of examples of [4 + 4]-photocycloadditions. The photodimerization of anthracene and its derivatives is one of the earliest known photochemical reactions of any type. More recently, naphthalenes, 2-pyridones and 2-aminopyridinium saltshave all been shown to undergo analogous head-to-tail [4 + 4]-photodimerization. Moreover, crossed [4+ 4]-photocycloaddition products can be obtained in some cases . Acyclic 1,3-dienes, cyclohexadienes and furan can form [4 + 4]-cycloadducts 211-214 with a variety of aromatic partners (Scheme 48). 

Few examples of photocycloaddition of the nitrogen-nitrogen double bond to alkenes are known and these are usually restricted to molecules in which the double bonds are held in close proximity to each other. A hitherto unknown [6 + 2] intramolecular addition to a benzene ring has been reported in the azoalkane (141) which is converted on irradiation into the 1, 2-diazetidine (142). Irradiation of 4-phenyl-4H-1,2,4-triazole-3,5-dione (143) in the presence of naphthalene, however, affords the [4 + 2] photoadduct... 

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