O-phenylene

Formation of a Quinoxaline. Heat together for 5 minutes under reflux 0 2 g. of phenanthraquinone dissolved in i ml. of glacial acetic acid and 0-2 g. of O -phenylene diamine also dissolved in i ml, of glacial acetic acid. The yellow substituted quinoxaline (p. 305) separates rapidly. Cool, filter and recrystallise from benzene m.p. 225 . 

Although this experiment is written as a dry-lab, it can be adapted to the laboratory. Details are given for the determination of the equilibrium constant for the binding of the Lewis base 1-methylimidazole to the Lewis acid cobalt(II)4-trifluoromethyl-o-phenylene-4,6-methoxysalicylideniminate in toluene. The equilibrium constant is found by a linear regression analysis of the absorbance data to a theoretical equilibrium model. 

It appears that all RHgX and HgR2 compounds are made up of linear R-Hg-X or R-Hg-R units, which could arise from sp hybridization of the metal. In some cases polymerization is necessary to achieve this linearity. Thus, for instance, o-phenylene-mercury, which could conceivably be formulated as... 

Diketones, like diacetyl and related synthons, react readily with o-phenylene-diamines or related reduced substrates to afford quinoxalines. Only when both synthon and substrate are unsymmetric are two isomers formed, and this simation has been largely avoided in recent literature. The following classified examples illustrate many of the possibilities available from such syntheses. 

Benzimidazoles have been prepared by direct condensation of o-phenylene-diamine 190 with a carboxyhc acid at 110 °C in water and under microwave irradiation (Scheme 69) [124]. Differently functionahzed benzimidazoles 192 were obtained with this method especially regarding the nature of the substituent on the imidazole ring. 

Reaction of commercially available 3-chlorotetronic acid 762, obtained by pyrolysis of methyl 2,4-dichloroacetoacetate at 140 °C in vacuo [235], with o-phenylene-diamine affords, after cyclization-oxidation with AgOAc, the quinoxaline lactone 763 in 69% yield [234] (Scheme 5.83). 

Concentration of the filtrate yields a second crop of impure product, which is recrystallized from toluene and then melts at 119-120°. The combined yield of pure white o-phenylene carbonate from the first and second crops is 107-116 g. (79-86%). 

We have also attempted to study the reactions of the tetrafluoro-o-phenylene di-radical (32) with benzene, by carrying out the photolysis of 1,2-di-iodotetrafluorobenzene in the presence of benzene. It is known that 1,2-di-iodoarenes give arynes on photolysis 70-72>. The only product derived immediately from o-dehydrotetrafluorobenzene was the 1,4-cyclo-adduct (24) which was, as expected, partially photoisomerised to (27) and a trace of (26) 73>. The photolysis resulted in the appearance of (24) and (27) before (26) was detected and hence we conclude that (26) was not a primary product. 

It is unlikely that the compound (27) is derived directly from the reaction of an excited benzene with tetrafluorobenzyne even though the compound (27) is formally analogous to the photo-adducts formed by the irradiation of olefins in benzene 74,75) A number of other products derived from the o-iodotetrafluorophenyl radical were also obtained 73>. These results suggest either that the tetrafluoro-o-phenylene di-radical (32) is identical with tetrafluorobenzyne or that if it is produced at a higher energy level it returns rapidly to the groundstate before it reacts with benzene. An alternative and perhaps more likely explanation is that the tetrafluorobenzyne formed arises by the concerted loss of both iodine atoms. 

Azolo[1,6]naphthyridines. Benzimidazonaphthyridines can be prepared from a one-pot reaction of o-phenylene-diamine, acrolein, and the cyclic keto ester 235 in the presence of molecular sieves and air (Equation 63) <2006SC1671>. 

Bi- and poly-thioethers with aliphatic backbones are produced by attack of RS on the appropriate haloalkane. This is the method of choice for RS(CH2)raSR (R = Me or Ph),26 MeC(CH2SR)3,27,28 MeS(CH2)raS(CH2)raSMe (n = 2 or 3) and MeS(CH2)raS(CH2) S(CH2) SMe.28,29 [Caution Some of these syntheses involve sulfur mustard derivatives as intermediates - these are very powerful vesicants and should be handled only with extreme care.] The other tridentates RS(CH2)3S(CH2)3SR (R = Et, Pr or Ph) may be obtained from nucleophilic attack by RS on the ditosylate TsO(CH2)3S(CH2)3OTs.30 Tetra-dentate thioethers involving o-phenylene interdonor linkages are also known.31 More recently the preparation and coordination chemistry of the silicon-apex derivative MeSi(CH2SMe)3 has been described.32... 

---