Naphthalene 4 + 3 cycloaddition reactions

Since dihydroarylethenes are more reactive than the corresponding fully aromatic compounds, their use in the cycloaddition reactions is preferred in order to carry out the reactions under mild conditions with higher yields. Some reactions of 3,4-dihydro-1-vinylnaphthalene (103) [33], 3,4-dihydro-2-vinyl-naphthalene (104) [34], and l,2-dihydro-4-vinylphenanthrene (105) [35] with 4-acetoxy-2-cyclopentenone (98) and 2-inden-l-one (106) are summarized in Schemes 5.11-5.13. 

The study of the cycloaddition behavior of l,l-dichloro-2-neopentylsilene, C Si =CHCH2Bu (2) [3], reveals the high polarity of the Si=C bond and a strong electrophilicity. The [4+2] cycloaddition reactions with anthracene (3), cyclopentadiene (4) and fulvenes (5) proceed as expected surprising, however, the Diels-Alder reactions with dienes are of lower activity, like naphthalene (6) and furans (7). 

Diarylmethylenecyclopropa[6]naphthalenes 14, unlike their benzene parent counterparts which give cycloaddition reactions at the cyclopropene bridge bond [10a], react on the exo double bond in Diels-Alder cycloadditions (see Sect. 2.1.1) [10b]. The reactions of 14 with the highly electron-deficient acetylenic(phenyl)iodonium triflate 584 give products 586a and 587, which are believed to derive from unstable primary [2 + 2] cycloadducts 585 (Scheme 82) [10b],... 

The growth step procedures for the cycloaddition reaction are very simple. Combination of an ethynyl-substituted dendrimer and an excess of the cyclo-pentadienone in a refluxing solvent such as o-xylene, diphenylether, or methyl-naphthalene (with b.p. higher than 130 °C) typically results in quantitative conversion within 24 h. The refluxing of the solvent is necessary to accelerate the elimination of the carbon monoxide in the cycloaddition. The purity of the resulting compounds was checked by MALDI-TOF mass spectrometry which showed quantitative reaction, facilitating work-up. By repeated precipitation in methanol, the pure product can be isolated as white amorphous powders in yields higher than 90%. 

Derivatives of the naphthalen-l,4 -imine ring system (2) have become available only since the discovery of cycloaddition reactions of benzyne, on the one hand, and the recent rapid development of isoindole chemistry on the other. 

H-stacking interactions have also been exploited to orientate olefinic moieties in a geometry suitable for photochemical cycloaddition reactions, and have been invoked by Coates et al. to explain the photodimerization and photopolymerization of mono- and diolefins carrying phenyl and perfiuorophenyl groups [43]. Matsumoto et al. reported the photodimerization of 2-pyridone in co-crystals with naphthalene-substituted monocarboxyhc acids, where the stacking of the naphthalene rings provides carbon-carbon distances appropriate for [4+4] cycloaddition [44]. 

By far the most important property of benzo[c] furans is their capacity to act as 471-components in cycloaddition reactions. Whereas the reactions described before 1969 were almost always of the Diels-Alder type, more recent investigations have shown that they can also participate in [7 4 + 714]-and [714 + TCgj-addition (Section IV,C). In this chapter Diels-Alder reactions will be discussed. Benzo[c]furans have been used for two main purposes. First, Diels-Alder adducts with olefinic compounds can conveniently be dehydrated to naphthalene derivatives or higher condensed hydrocarbons not easily accessible by other methods second, benzo[c]furans are excellent... 

Heterocyclic systems with one heteroatom. Condensed heteroaromatic cations are reactive in [2 + 4] cycloaddition reactions with inverse electron demand. For instance, 2-benzopyrylium salts 403 react with vinyl ethyl ether to afford naphthalene derivatives 405 in good yields via initial adducts 404 <1990KGS315>. Similar transformations (Bradsher reaction) are also known for isoquinolinium salts <1984CC761>. 

Cycloaddition reactions with anthracene [3], cyclopentadiene [3] and dienes of lower activity, such as naphthalene [4] and furans [6], are well known. In this contribution, we describe the competitive formation of [4+2] and [2+2] cycloaddition compounds resulting from Cl2Si=CHCH2tBu (3) and 6,6-dimethylpentafulvene. 

The 1,2-cycloaddition reaction can take place in an intramolecular manner (equation 63), although in this example the initial excitation involves the aromatic group . A reaction of a different type is thought to be involved in the first stage of the formation of azulene or naphthalene photodimers from diphenylacetylene (equation 64), though here it is claimed that an intermediate benzocyclobutadiene species has been detected . The intermediate isomer of diphenylacetylene is formed via the triplet state and is relatively long-lived at — 10 °C. The major dimers formed are 1,2,3-triphenylazulene and 1,2,3-triphenylnaphthalene hexaphenylbenzene and octaphenylcubane are also produced . 

Formation by a concerted cycloaddition reaction A phenantlirene tnolecuie would be formed in two ways as below tlie [4 + 2] cycloaddition of biphenyl with two benzene molecules followed by a retro Diels-Alder reaction and by dehydrogenation the 14 + 2] cycloaddition of naphthalene witli benzene followed by the retro Diels-Alder reaction and dehydrogenation. An anthracene molecule would be formed by the [4 + 2] cycloaddition of naphtlialene with benzene followed by retro Diels-Alder reaction and by dehydrogenation. In these cases, tlie yield relation would be phenanthrene anthracene, because biphenyl is produced more abundantly than is naphtlialene during shock reaction. This statistical consideration fits the experimental results. 

Acetylenes can undergo a number of thermal and transition metal promoted cycloaddition reactions. Besides the [2 + 2 + 2] cycloaddition (see Sect. 5) the reaction of acetylenes with late transition metal (so-called Fischer ) carbenes is noteworthy for the synthesis of highly and regioselectively functionalized naphthalene derivatives (Dotz reaction), while the co-cycloaddition of acetylenes with alkenes and carbon monoxide gives cyclopentenones (Pauson-Khand reaction) [159,160]. 

K. In addition, it was found that the irradiation of 22 in benzene in the presence of both cis- and rans-pentenes (0.05 to 3 M) produces a mixtiu-e of aziridines, which is typical of the presence of both singlet and triplet nitrene cycloaddition reactions. The triplet-triplet absorption spectrum of azide 22 was detected, and it was found that naphthalene inhibits the photoreaction of 22 by quenching of its triplet state. It was concluded, therefore, that the ground state of nitrene 23 is a triplet and that it is formed exclusively upon sensitized photolysis of azide 22 through the triplet state of 22. 21 Nq isocyanate was detected in the photolysis products of 22. 

Inter molecular Additions to Cyclohexenones and Related Systems. Calculations have been reported that deal with a transition state analysis of the regioselectivity encountered in triplet-state (2 + 2)-cycloaddition reactions of cyclohex-2-enone. Diastereoselective (2 + 2)-cycloaddition of ethene to cyclohexenone carboxylates in the presence of chiral auxiliaries has been described. Yields of bicyclo[4.2.0]octanone derivatives can be obtained with de as high as 81%. The enone (16) can be tethered to a polymer substrate via the tether group R. Irradiation of this material in toluene with ethene at —78°C gives a 68% yield of the adduct (17). The de of the product is reasonable at 72%. Addition of 1,1-diethoxyethene to the cyclohexenone (18, R = Ph) results in the formation of the two stereoisomeric head-to-tail regioisomers (19) and (20). The outcome of the reaction is dependent on the rate of formation of 1,4-biradical intermediates. This can be seen in the dependence of the cisjtrans ratio on the solvent and on the temperature at which the reaction is carried out. Thus with enone (18, R = Ph) in acetone at 3°C, a cjt ratio of 4.4 is obtained, and this changes to 2.1 at —40°C. In acetonitrile the cjt ratio is only 1.9 at the same temperature. With the other derivative of (18), the cjt ratio is 1.3 in acetone and 0.8 in acetonitrile. Photoaddition of ethene to the enone carboxylate [21, R = (-)-8-(2-naphthyl)menthyl] results in the formation of the diastereoisomers (22) and (23) with a de of 56% at —78°C. The diastereo-selectivity can be enhanced by the addition of naphthalene derivatives to the solution. Thus with naphthalene, a de of 71% is obtained, and this can be increased to 83% with 1-phenylnaphthalene. ... 

The [4 + 2]cycloaddition reactions of benzo[c]thiophenes have been further exploited. 4,5,6,7-Tetrafluorobenzo[c]thiophene undergoes cycloaddition to DMAD and tetrafluorobenzyne this is followed by sulfur extrusion, yielding a naphthalene and an anthracene, respectively <90JCS(P1)1919>. The Diels-Alder reaction of l,3-bis(4-methoxyphenyl)benzo[c]thiophene, with iV-phenylmaleimide proceeds normally. However, with a sterically hindered substrate like l,3-bismesitylbenzo[c]-... 

Arynes, such as benzyne (1,2-dehydrobenzene), also undergo Diels-Alder cycloaddition reactions. Benzyne, CelTj, is a highly reactive species and can be prepared by elimination of a suitably substituted benzene derivative. It reacts in situ with various dienes such as furan, cyclopentadiene, cyclohexadiene and even benzene and naphthalene to give bicyclic or polycyclic cycloadducts (3.15). Analogous addition reactions are shown by dehydroaromatics in the pyridine and thiophene series. 

Scheme 77 Asymmetric cycloaddition reaction on o-(l-dimethylaminoethyl)-naphthalene palladium template 235...

Electrophilic substitution and other reactions of naphthalenes (alkylation, acylation, condensation and migration in acidic ionic liquids have been reported. Anthracene undergoes photochemical [4+4] cycloaddition reactions - in acidic chloroaluminate(III) ionic liquids. One interesting study ineluded a one-pot synthesis of anthraquinone from benzene giving a 94% yield. In general a much wider range of redox products are formed than occur in conventional solvents the strong Bronsted acidity of die ionic liquid induces protonation of anthracene, by residual traces of HCl, to form an anthracenium species which couples readily via photochemically driven electron transfer mechanisms. 

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