Benzynes, also

Benzyne also reacts with carbon disulfide to produce the tetrathiafulvalene derivative (300) (75S38, 74CC166). Dithioacids react with phenylacetylene to form 1,3-dithioles (301) (80TL2247). 

The term benzyne denotes orfho-benzyne, also known as 1,2-dehydro-benzene or in Chemical Abstracts as 1,3-cyclohexadien-5-yne. The last name is misleading, since benzyne lacks two ortho hydrogen atoms of benzene but not the stabilization associated with delocalization of double bonds. It is commonly represented by any of the structures 1-3. There is now a very... 

Benzyne also reacts with compounds containing nucleophilic carbon atoms such as enolates and aryl anions. Intramolecular nucleophilic addition to an aryne by the ortho ring carbon atom of another benzene ring substituted... 

Pacquer et al. also recognized a second series of intensely colored 1 1 adducts, the trithiapentalenes 153, from benzyne and 5-aryl-l,2-dithiole-3-thiones (151).93 Although very little of 153 (Ar = Ph) was obtained (< 1%), p-anisyl, p-tolyl, and p-chlorophenyl compounds were formed in higher yields. Unsuccessful attempts to achieve the conversion 152 - 153 render more likely an independent pathway for the formation of 153, e.g., one involving an initial 1,2-cycloaddition of benzyne to the exocyclic C=S bond of 151. Derivatives of the related l,2,4-dithiazole-3-thione system 160 and benzyne also afford two series of 1 1 adducts 161 and 162 corresponding to 152 and 153, respectively.93... 

Benzyne also reacts with oxiranes and aziridines. ... 

As a reactive dienophile ortbo-benzyne also participates in the ene reaction. Thus, alkenes with allylic hydrogen can undergo concerted reaction to give substituted benzenes. However, the yields are rarely good. Cycloaddition of ortho-benzyne to alkynes should in principle give benzocyclobutadienes. Such intermediates are highly unstable and not surprisingly are not isolated. Instead, the products, formed in low yield, derive from further reaction with another molecule of ortho-benzyne or by dimerization (Scheme 7.32). 

The same group found that a four-membered ring fused to a benzyne also had a powerful regioselective directing effect in the [2+2] cycloadditions of benzyne, presumably through the severe ring strain [97]. In the reaction of ketene silyl acetal... 

Although nucleophilic aromatic substitution by the elimination-addition mecha nism IS most commonly seen with very strong amide bases it also occurs with bases such as hydroxide ion at high temperatures A labeling study revealed that hydroly SIS of chlorobenzene proceeds by way of a benzyne intermediate... 

Benzyne may also be generated by treating o bromofluorobenzene with lithium In this case o fluorophenylhthmm is formed which then loses lithium fluoride to form benzyne... 

Nucleophilic aromatic substitution can also occur by an elimination-addition mechanism This pathway is followed when the nucleophile is an exceptionally strong base such as amide ion m the form of sodium amide (NaNH2) or potassium amide (KNH2) Benzyne and related arynes are intermediates m nucleophilic aromatic substitutions that pro ceed by the elimination-addition mechanism... 

N-Arylation of azoles is achieved either by using arynes, activated halobenzenes (e.g. dinitro) or under Ullmann conditions. Thus benzyne reacts with imidazoles to give N-arylimidazoles (70AHC(12)103), and these compounds have also been prepared under modified Ullmann conditions. 

Oxidation of 1 -aminobenzotriazole also yields benzyne under mild conditions. An oxidized intermediate decomposes with loss of two molecules of nitrogen. ... 

Benzyne can also be generated from o-dihaloaromatics. Reaction of lithium amalgam or magnesium results in formation of a transient organometallic compound that decomposes with elimination of lithium halide. l-Bromo-2-fluorobenzene is the usual starting material in this procedure. 

Benzyne may also be generated by treating o-bromofluorobenzene with lithium. 

Enamines have also been shown to react with benzyne (68) to give benzo-cyclobutenes. 

The addition-elimination mechanism involves two intermediates, a chlorophenyl anion and benzyne. A simple displacement mechanism can be ruled out because reaetion of ort/io-chlorotoluene gives not only ort/io-methylphenol but also meto-methylphenol. 

The aporphinoid alkaloid PO-3 (129) was also prepared by intermolecular benzyne cycloaddition between 1-methylene isoquinolines 148 and arynes derived from 147 (Scheme 53). The alkaloid was finally isolated by means of preparative thin layer chromatography (91JOC2984). 

Benzyne 72, 184ff., see also Aryne Bifunctional catalysts 361 Bilirubin, in azo coupling 323 f. 

The same 1 1 product ratio was found with iodobenzene-l-14C. This result clearly indicates that the same intermediate intervenes with both halides. The most likely candidate is benzyne, as shown, which would easily accommodate the distribution of the label. Also, the intermediate is not likely to contain Cl or I, because its selectivity ratio in the second step would then not be the same. 

It has been found that aryl groups can also be introduced into the a-position of sulphoxides. Corey and Chaykovsky have demonstrated that chlorobenzene reacts at room temperature with an excess of sodium methylsulphinyl carbanion to give methyl benzyl sulphoxide in 41% yield. The authors believe that a benzyne intermediate may be involved in the reaction400,401 (equation 174). 

---