Cyclohexadienes anthracene

Only one activating group on the alkyne is necessary for the cycloaddition to occur, and the monophosphorylated acetylene reacts as readily as the diphosphorylated one. Dienes such as isoprene, 2,3-dimethyl-l,3-butadiene, cyclopentadiene, l,3-cyclohexadiene, " anthracene, 9-methylanthracene, ° d-methyl-S-propoxyoxazole, l-phenyl-3,4-dimethylphosphole (Scheme 1.25), and a-pyronc have been employed. 

Other dienes, such as cyclohexadiene, anthracene and cyclopentadiene have also been reacted with a-oxo sulfines. The cycloaddition of a-oxo sulfines with 2-trimethylsilyloxy-1,3-butadienes afford thiacyclohexane-3-one S-oxides after hydrolysis . ... 

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 type97. More recently, naphthalenes98, 2-pyridones" and 2-aminopyridinium salts100 have all been shown to undergo analogous head-to-tail [4 + 4]-photodimerization. Moreover, crossed [4+4]-photocycloaddition products can be obtained in some cases101. Acyclic 1,3-dienes, cyclohexadienes and furan can form [4 + 4]-cycloadducts 211-214 with a variety of aromatic partners (Scheme 48). 

Endo and coworkers98 were able to catalyze the Diels-Alder reaction between acrolein and 1,3-cyclohexadiene by using a novel organic network material built up of anthracene-bisresorcinol derivatives which were held together by intermolecular hydrogen bonds. The suggested catalytic cycle was composed of sorption of the reactants in the cavities of the material, a pre-organized intracavity reaction, and desorption of the adduct. 

Cyclopentadienes, 1,3-cyclohexadienes, 1,3-cycloheptadienes, as well as furan and aklyl-substituted furans, have been investigated as substrates of photosensitized oxygenation reactions, while aromatic compounds such as anthracenes and tetracenes as well as aryl-substituted carbo-and heterocyclic pentadienes were studied in direct and indirect (photosensitized) photooxygenation reactions. 

Early examples of electron transfer processes are shown in equations (2), (12), and (13). Birch in 1944 followed up the findings of Wooster, and demonstrated that Na metal and ethanol in ammonia reduce benzene, anisole, and other aromatics to 1,4-cyclohexadienes. Birch speculated about the mechanism of this reaction, but did not explicitly describe a radical pathway involving 55 (equation 87) until later, as described in his autobiography. Electron transfer from arenes was found by Weiss in 1941, who obtained crystalline salts of Ci4H]o from oxidation of anthracene. ... 

Photolysis, in the presence of oxygen, of alkenes containing an ally lie hydrogen atom leads to the formation of hydroperoxides. The sensitized process is more efficient, and often yields photoproducts different in structure from those obtained by nonsensitized photooxidation. Cyclohexadiene and related dienes on photolysis in the presence of oxygen yield the transannular peroxides. Thus, on photosensitized oxidation, a-terpinene (410) is converted into ascaridole (411).435 The equivalent process is not, in general, observed in acyclic dienes. Certain polynuclear aromatic hydrocarbons, such as anthracene and naphthacene and including the heterocycles 5,10-diphenyl-1-... 

Photocycloadditions of more condensed aromatic hydrocarbons such as benz[fl]anthracene, naphthacene, di ben z a, / an(hracene, dibenz[aj]anthracene, dibenz[a,cjanthracene, with 1,3-cyclohexadiene, gave (4 + 4), (4 + 2), and (2 + 2) cycloadducts [176,177,221,222] (Scheme 47). 

Thus, cycloaddition of 63 with cyclopentadiene afforded a mixture of exo- and tro/o-stereoisomers in 1 15 ratio. In contrast, cycloaddition of 63 with 1,3-cyclohexadiene afforded a single tro/o-stereoisomer. The reaction of 63 with anthracene afforded the expected cycloadduct in excellent yield. When the diene is acyclic, for example, 2,3-dimethylbutadiene, a single cycloadduct was formed in 67% yield (Equation 16). In contrast, 2,4-hexadiene yielded a mixture of two stereoisomers in 2.9 1 ratio, respectively (Table 17). 

Numerous photodimerization studies of 1,3-cyclohexadiene 36 have been reported (Sch. 9). Thermal cycloaddition yields a 4 1 mixture of endo/ exo [4+2] adducts 37 and 38 in modest yield. Irradiation of the diene in cyclohexane near its 2max of 254 nm yields very little dimer, but irradiation at 313 nm leads to a mixture of dimers, favoring the [2+2] adducts 39 [37]. The use of y-radiation produces similar mixtures [38,39]. A triplet sensitizer leads to largely the [2+2] adducts plus exo 38 and little of the endo [4+2] isomer 37 [40]. When the photochemistry is conducted in the presence of the electron acceptors anthracene 41, LiC104-42 or pyrylium 43, only [4+2]... 

Anthracene and substituted anthracenes are also known to sensitize the dimerization of 1,3-cyclohexadiene, another triplet state process [E(7,) for 1,3-cyclohexadiene = 53 kcal/mol] [28]. In similar experiments, the 72 state of naphthalene was also shown to undergo energy transfer to quenchers [29]. 

The first direct time-resolved evidence for energy transfer from an upper excited triplet state in solution at room temperature was published in 1987 [50]. This study made use of the two-color technique to photoexcite the 7, state of benzophenone, 70, in benzene solvent. As the extensive (almost quantitative) triplet depletion was not accompanied by any product formation, it was concluded that the excitation energy was transferred to the triplet manifold of the benzene solvent. The energetics of this donor-acceptor system are certainly conductive to this process. The benzophenone 7, and Tn energies (69 kcal/mol and ca. 120 kcal/ mol, respectively—the second photon in the two-color excitation provides roughly 50 additional kcal/mol to the 71 state) bracket the benzene 7j energy (85 kcal/mol) and therefore benzene acts in the same way toward benzophenone as 1,3-cyclohexadiene acts toward anthracene, i.e., as an exclusive upper triplet energy accepter. 

In 1978, Weiler and Brennan [63] reported the use of racemic 4-zso-thiazolin-3-one-l-oxide (54) as a dienophile, the structure of which could be considered to be a cyclic sulfinyl acrylamide. It undergoes facile cycloaddition (temperatures under 60 °C are required) with cyclop entadiene, 2,3-dimethyl-1,3-butadiene and 1,3-cyclohexadiene, to afford only one product in each case (Scheme 28). Reactions with anthracene and hexachloro cyclop entadiene required temperatures above 100°C, and were effectively catalyzed by A1C13. Although the stereochemistry of the obtained adducts was not ascertained, the authors suggest that the major one is the result of an endo-approach, which must be favored on the basis of mechanistic considerations. 

A triplex has been proposed as an intermediate in some photoreactions. Yang and co-workers [54] found that addition of 1,3-dienes to anthracene excimers leads to different products than does its adition to monomeric excited arenes. Lewis and co-workers [55, 56] found that stilbene excimers can be intercepted by dimethyl fumarate to give an oxetane through a presumed triplex. More recently, Schuster and co-workers [57,58] studied the Triplex Diels-Alder reaction of 1,3-dienes with enol, alkene, and acetylenic dienophiles. Take 9,10-dicyanonaphthalene (DCN)/indene (IN)/l,3-cyclohexadiene (CHD) system as an example ... 

In another example, the hexaacetylene 109 - after deprotection with potassium carbonate in methanol - is subjected to typical Bergman trapping conditions, resulting in the formation of the anthracene derivative 110 [61]. As a third, more complex illustration, the aroma-tization of the triacetylene 111 may be considered. Here, the 1,4-diradical intermediate faces another triple bond as an internal trap, and, after hydrogen transfer from 1,4-cyclohexadiene, the tricyclic allylic alcohol 112 is produced [61]. 

Summary New silacyclopropanes were synthesized quantitatively under mild thermal conditions by reaction of olefins with cyclotrisilane (cyclo-(Ar2Si)3, Ar = Me2NCH2QH4) 1, which transfers all of its three silylene subunits to terminal and strained internal olefins. Thermolysis of silacyclopropanes 3a und 3b indicated these compounds to be in a thermal equilibrium with cyclotrisilane 1 and die corresponding olefin. Silaindane 13 was synthesized by reaction of 1 with styrene via initially formed 2-phenyl-1-silacyclopropane 3d. Reaction of 1 with conjugated dienes such as 2,3-dimethyl-l,3-butadiene, 1,3-cyclohexadiene or anthracene resulted in the formation of the expected 1,4-cycloaddition products in high yield. 

When 1 was stirred with three equiv. 2,3-dimethyl-l,3-butadiene at 40 °C for 12 h, silacyclopentene 14 was formed quantitatively [10a]. In a similar manner, 7-silanorbomene 15 [12] and dibenzo-norbomadiene 16 were formed without any side products by reaction of 1 with 1,3-cyclohexadiene or anthracene, respectively. 

A general route to thioaldehydes is the base-induced 1,2-elimination of sulfenate derivatives, described initially by Kirby et al. In this reaction, phthalimide derivatives, e.g. (25), react with Et3N to generate a thioaldehyde, which is subsequently trapped by dimethylbutadiene to yield product 26 [83CC423 85JCS(Pl)1541]. Other dienes used in this study include thebaine, cyclohexadiene and anthracene. 

Mixed photocycloadditions of anthracene and conjugated polyenes yield products that correspond to a concerted reaction path, as well as others that are Woodward-Hoffmann-forbidden and presumably result from noncon-certed reactions. For example, the reaction of singlet-excited anthracene with 1,3-cyclohexadiene yields small quantities of the [ 4 +, 2J product 72 in addition to the allowed 4, +, 4J product 71. 

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