Anthracene reaction with benzyne

Reactions with Benzyne. A-Methylimidazole reacts with benzyne to generate either Al-methyl-Al-arylimidazolium salts or aryl amines containing anthracene. The product generated depends on the reaction stoichiometry using a 3 1 ratio of NMI to aryne gives aryl amines, whereas a 1 3 ratio produces salts (eqs 11 and 12). 

The formation of anthracene in reactions of 185 and 186 with benzyne, which was unexplained by Wittig et aZ., possibly is due to an alternative reaction of the intermediate zwitterion (202) with another molecule of benzjme or with a benzyne precursor. Benzyne reacted with the isoindole (206) to give the tetramethyltriptycene (208) and, in a separate run using excess of the benzyne precursor, W-benzylcarbazole. The latter product would appear to be made up of the iV-benzyl group from an intermediate anthracen-9,10-imine (207) and two molecules of benzyne. Mass spectral evidence also implicated the adduct 207, and the formation of 208 was attributed to benzyne-induced deamination of 207 to 1,4,9,10-tetramethylanthracene, which was trapped by further addition of benzyne across the 9- and 10-positions. 

Aromatic compounds can also behave as dienes.858 Benzene is very unreactive toward dienophiles very few dienophiles (one of them is benzyne) have been reported to give Diels-Alder adducts with it.859 Naphthalene and phenanthrene are also quite resistant, though naphthalene has given Diels-Alder addition at high pressures.860 However, anthracene and other compounds with at least three linear benzene rings give Diels-Alder reactions readily. The interesting compound triptycene can be prepared by a Diels-Alder reaction between benzyne and anthracene 861... 

Triptycene is the Diels-Alder cycloaddition product from the reaction of benzyne with anthracene (compound A). Although anthracene is aromatic, it is able to undergo cycloaddition at the center ring with a dienophile because the adduct retains the stabilization energy of two benzene rings. 

As benzothiophene was a product of both the reaction of benzyne with thiophene and the pyrolysis of thiophene alone (Fields and Meyerson, 1966d), we investigated the reaction of benzyne with benzothiophene. Pyrolysis of a mixture of phthalic anhydride and benzothiophene gave the products shown in Table 11. Anthracene and dibenzothiophene probably arose via 1,2-, and phenanthrene via 1,4-addition to the thiophene ring ... 

The reaction of anthracene with benzyne gives a product, C2oH 4, that shows only four peaks in its l3C-NMR spectrum. Show the structure of this product and explain its formation. 

In Chapter 48 diphenyliodonium-o-carboxylate is utilized as a benzyne precursor in the synthesis of 1,2,3,4-tetraphenylnaphthalene. For reasons unknown, the reaction of anthracene with benzyne generated in this way proceeds very poorly and gives only a trace of triptycene. What about the... 

Thus, 1,2,3,4-tetramethyl Dewar naphthalene is formed by reaction of benzyne with tetramethylcyclobutadiene (25)26>. Unsubstituted Dewar anthracene is obtained by a stepwise reaction (26)27). This compound violently isomerizes at 73 °C to anthracene. This shows that a terf-butyl group greatly affects the stability of the above mentioned 9-tert-butyl Dewar anthracene. 

Based on our hypothesis that the acetylene was too flexible for 15/16 to function as a brake, we redesigned the system by deleting the acetylenic unit and connecting the pyridine directly to the triptycene as in 22. Unfortunately, the synthesis of 22 proved unsuccessful, because the reaction of the anthracene of 23 with benzyne then failed (Scheme 4). 

The same authors have also reported the reactions of other arynes with thiophen and the reactions of benzyne with 54.57,58 They present speculative reaction mechanisms to account for the formation of products, which in many cases are imperfectly identified from mass spectra alone. For example, although they acknowledge an inability to distinguish between anthracene and phenanthrene,58 they claim, in the same article, both of these as products of distinct reactions of benzyne with 54. Two minor products are claimed to be 59 and 60, respectively, and to provide evidence for the intervention of 2,3-dehydrobenzo[h] thiophen (58). 

N-phenylation. The further reaction of 87 and 88 with benzyne to give 9-aminoanthracene derivatives 91 (cf. the mechanism outlined in Scheme 12) is blocked by the presence of substituents at the bridgehead positions as in 86. Anthracene (9%) is also produced from the reaction of 87 with benzyne,48 and the formation of the tetramethyltriptycene 93 from benzyne and the isoindole 92 is attributed to a similar deamination of an intermediate anthracen-9,10-imine.68 Deamination of 86 and 87 is more conveniently accomplished by treatment with hydrogen peroxide.72... 

Anthranil (119) and benzyne (from oxidation of 9 with lead tetraacetate) afford acridine (5%)81 depending on the sequence of bond forming and breaking, an oxygen-bridged cycloadduct and/or acridine N-oxide (120) may be intermediates in this reaction (Scheme 15), although 120 is known to react with benzyne in a different sense (Section IX). The addition of benzyne to oxazoles leads, ultimately, to anthracene derivatives in high overall yield.82b... 

Alternatively, reduction of 176 with sodium borohydride (probably to a dihydropyridine, although this intermediate was not characterized) followed by thermolysis in acetic acid or acetic anhydride affords anthracene (93%) and pyridine or hydropyridines. These reaction sequences have been employed for the synthesis of overcrowded anthracene derivatives containing substituents with unfavorable peri interactions100 of particular interest is the conversion of 178 via its 1 2 adduct with benzyne into the pentaphenes 179 and 180. 

Benzynes and substituted benzynes react with isoindoles to give the 9,10-dihydroanthracene-9,10-imines (92).33 A considerable number of substituted compounds of this type have been prepared.27 Triptycene derivatives (i.e., the benzyne adducts of the anthracene system) have been encountered as unexpected products from the reaction of benzyne with 2-benzyl-1,3,4,7-tetramethylisoindole.114... 

The reaction with naphthoselenadiazole 400 took still a different course. Benzyne (from benzenediazonium carboxylate) gave 403 in very low yield (3%). The initial product is thought to be 401 (that is, 400 reacts with benzyne in the same manner as anthracene, to give a heterotriptycene). Although 401 could not be isolated, 400 did give an analogous... 

The high reactivity of benzynes as dienophiles in Diels-Alder reactions has also been observed in reactions with aromatic hydrocarbons, a class of compounds usually considered as inert as dienes. In a two-step synthesis of triptycene di- and tetracarboxylic acids, arynes generated in situ from anthranUic adds 158 cydized with anthracenes 159 affording di- or tetramethyltriptycenes 160 in 41-69% yields (Scheme 12.47) [85], Acids 161 were obtained after subsequent oxidation of the cycloadducts 160 with potassium permanganate. 

A simple one-pot synthesis of anthracenes uses the reaction of the enolate of acetaldehyde with bromozene. The enolate, generated by the decomposition of THF with a strong base, reacts with benzyne to give a benzocyclobutene (593) which reacts with a second benzyne, via its valence isomer (594), to give the dihydroanthracenol. 

Three rotameric forms of (26) have been isolated at room temperature. In fact Diels Alder addition of dimethylacetylene dicarboxylate to 2,3-dichloro-9-(l,l-dimethyl-2-phenylethyl)anthracene produces only the ap-rotamer (26). The other rotamers can be isolated by thermal equilibrium at 150 °C and subsequent chromatographic separation. Reaction of benzyne with the above anthracene yields only the d,/-triptycene derivative, and 4,5-dichlorobenzyne addition to 9-(l,l-dimethyl-2-phenylethyl)-... 

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