Dibenzo diazocine ring

Proton and C nuclear magnetic resonance (NMR) analyses of a variety of 1,4-diazocine derivative have been reported, in the context of both detailed conformational analysis and assessment of potential aromaticity as well as routine structural characterization. Fully unsaturated 1,4-diazocines appear to be represented only as their dibenzo[A/] and dibenzo[e, ] derivatives. A variety of NMR analyses have confirmed or demonstrated the nonplanarity of the diazocine ring in (12 X = NMe,... 

Dibenzo[c,g][l, 2]diazocine (3) can be reduced with zinc in ethanol to the dihydro derivative 9.22 which formally exhibits a lOre-electron conjugation (see also ref 28). The UV and H NMR spectra of 9 indicate some resonance stabilization of the eight-membered ring. 

Benzodiazocine and dibenzo[Z>,/][ 1,4]diazocine-diones (220) and (218) are obtained by condensation of diethyl succinate and phthalate, respectively, with o-phenylenediamine (69JOC2138). Contrary to an early report, the use of phthaloyl chloride leads to other products and not the tricyclic diazocine. The dibenzo derivative is also formed in the oxidation of diazabiphenylene (219) (78T495). Ring contraction of (218) occurs readily on heating or on treatment with PCI5 or with base. 

The tetrahydrodibenzo[6,/][l,4]diazocines (458) and the tetrahydrodibenzo[6,/]-[l,5]diazocines (459), which have two nitrogens in the heterocyclic ring, as well as their sulfur analogs (460) and (461) show conformational properties similar to those of the monoaza compound (456). Typical data are included in Table 3. The assignments of conformations and transition states for these dibenzo derivatives are supported by force-field calculations and by detailed dynamic NMR measurements <73JCS(Pl)205>. 

The enantiomerization of 6,7-dihydro-dibenzo[///][l,2]diazocine-5,8-dione 2 was investigated using quantum-mechanical methods. At the density functional theory (DFT) B3LYP/6-31G(d,p) level, two enantiomeric -symmetric transition states (TSs) and two enantiomeric pathways were found with a calculated barrier of 155.6 kj mol-1. The pathways can be divided into two steps one involving primarily inversion of the amidic bridge and the other movement of the aromatic rings <2004TA537>. 

Saunders and Sprake cyclized the amino ester and acid 14 and obtained the dibenzo[h,/]-l,4-diazocine 15. Dehydrosulfonation of 15 (R = alkyl) afforded ring-contracted products (see Section IV,C)(72JCS(P1)1964). Cycli-zation of the diamino acid 16 using DCC and triethylamine resulted in formation of 1,4-diazocinone 17. This compound was also prepared by a ring-expansion route (see Section II,B,4) (74JOC1710). 

A number of 1,4-diazocines have reacted to form imidazoles and fused-ring analogs. Beckmann rearrangement of the dioxime 171 yielded isoindolo-benzimidazole 172 (R = Cl, R = H) or 172 (R = H, R = Cl), most likely via rearrangement of an initially formed dichloro- 57 (57JCS1900). Dibenzo-diazocinedione 57, when heated with phosphorus pentachloride, afforded an... 

The 1,2-dioxocin ring system has received a rather surprising amount of attention, at least in relation to the other compounds discussed in this chapter (with the exception of the 1,2-diazocines). The vast majority of these reports deal with essentially two compounds, namely the 5,8-dialkoxy-5,8-dihydro-dibenzo[fi /][l,2]dioxocins (50) obtained from the ozonolysis of phenanthrene, and the corresponding 5,8-dione (51) ( diphenoyl peroxide ), but a substantial number of other derivatives have also appeared since the publication of CHEC-I in which only a single derivative was reported. 

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