1.2- dihalobenzene

In contrast, benzenethiolate anions react at the sulfur atom (Scheme 28) [146-149] from 1,2-dihalobenzenes and the 1,2-dithiolate dianion, dithiin is obtained [148]. Analogous substitutions are observed with diarylphosphites and other phosphorus nucleophiles [150-152], as well as with arylarsenides... 

Such dilithium reagents should make available many of the triptycenes suggested in Fig. 1, but the recent withdrawal of (the very expensive) 1,2-diiodotetrafluorobenzene from commercial catalogs is regrettable. Unfortunately, 1,2-dilithiobenzene cannot be prepared from the reaction of 1,2-dihalobenzenes with either lithium or alkyl-lithium reagents due to the exceedingly rapid formation of benzyne ... 

Another way to obtain suitably substituted diphenylamines is the condensation of o-aminophenols with activated 1,2-dihalobenzenes.24 The reaction was performed in nonalkaline medium. It is interesting... 

Reactions of Miscellaneous Haloketones and Acid Chlorides. - The reactivity of anions such as (91) with 1,2-dihalobenzene (a. 1,2-diiodo, b.l-chloro-2-iodo and c. l-bromo-2-iodo) derivatives has been studied. The irradiations are brought about in DMSO as solvent. The reaction affords (92) as the principal product in variable yields (71 % from b, 86% from c and 50% from a), depending on which of the arene derivatives is used. The other product (93,17%) is formed only from reaction with o-diiodobenzene. The irradiation of the acid fluoride CF3CF2C(0)F has been described as an efficient route for the production of the radical, CF3CF2. This radical can recombine with CFO to afford the starting... 

Dihalobenzenes give monomagnesium halide reagents that are often unstable and eliminate Mg halide and form benzyne . In a few cases 1,2-bis-magnesium halide reagents are obtained, e.g., from 3,4-dibromotoluene , 1,2-diiodobenzene and... 

Although the vast majority of stepwise polar additions to ortho-benzyne involve nucleophilic attack on the aryne, electrophilic attack is also possible provided that the aryne is generated by a method that does not involve strongly basic conditions. Few such additions are synthetically useful, with the exception of the formation of 1,2-dihalobenzenes by reactions of ortho-benzynes with halogens, although alternative mechanisms initiated by nucleophilic attack of halide may be envisaged. Radical reactions of ortHo-benzyne, on the other hand, are extremely rare. 

In a transition metal-ffee one-pot regioselective Smiles rearrangement process at ambient temperature, 2-mercaptonicotin(benz)amides 151 reacted with 1,2-dihalobenzenes 152 to afford fused l,4-thiazepin-5(4Jl) ones 153 in good-to-excellent yields (14JOC8040). 

In 2011, Bhanage and co-workers reported a carbon monoxide-free one-step synthesis of phthalimides by using formamides as an amine and CO source. With POCI3 as the activator, various phthalimides were produced in moderate to excellent yields (Scheme 2.2). In addition to 1,2-dihalobenzenes, 2-iodobenzoic acid and methyl 2-iodobenzoate can be applied as substrates for phthalimide preparation with formamides as an amine and CO source as well. This methodology was extended and applied in the synthesis of isobenzofuran-l(3/f)-one (70% yield) by using o-iodoben l alcohol as the substrate. 

The Cu" complexes can be prepared directly from trifluoromethyl substituted 1,2-dihalobenzenes in the course of Rosemund-Braun reaction with copper(I) cyanide (Scheme 25). Thus, reaction of 3-, 4-trifluoromethyl and 3,5-difluoromethyl substituted 1,2-dichlorobenzenes 102a-c with CuCN in quinoline (Qn) leads to Cu" complexes of a- or 3-tetrafluoromethyl- or a,p -octatrifluoromethyl-phthalocyanines 103a-c [71],... 

A plausible mechanism of the reaction involves the formation of compound 406 by the nucleophilic substitution by 405 on 2-halonitroarenes 383, 404 or 1,2-dihalobenzenes (see Sect. 2.7.3) and the formation of carboxamide anion 408. Finally, an intramolecular nucleophilic reaction of 408 with the displacement of the leaving group by carboxamide anion would lead to pyrrolo[l,2-a]quinoxaline 406 (Scheme 2.73). 

Methyl-substituted arylboronic acids underwent cross-coupling/C—H activation cascade with various 1,2-dihalobenzenes, including l-chloro-2-halobenzenes in the presence of PdOAc)2/PCy3 as a catalyst and M2C03/rBuC02H (M = K, Cs) as a base [67], For example, 6,12-dihydroindeno[l,2- ]fluorene 194 was obtained in 73% yield from 191 and 192 (Scheme 22.44). 

Takahashi s group reported an effective copper-promoted method for the coupling of 1,2-dihalobenzenes and 1,2,4,5-tetrahalobenzenes with zirconacyclopentadienes to produce polysubstituted naphthalenes and anthracenes, respectively (X = Y = halogen in Scheme 25.1 see also Chapter 11) [lb,2]. 

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