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Relevant academic research and scientific papers

Metal-free deoxygenation and reductive disilylation of nitroarenes by organosilicon reducing reagents

A metal-free deoxygenation and reductive disilylation of nitroarenes was achieved using N,N’-bis(trime-thylsilyl)-4,4’-bipyridinylidene (1) under mild and neutral reaction conditions, and a broad functional group tolerance was possible in this reaction. Mono-deoxygenation, giving a synthetically valuable N,O-bis(trimethylsilyl)phe-nylhydroxylamine (7a) as a readily available and safe phenylnitrene source from nitrobenzene, and double-deoxy-genation, giving N,N-bis(trimethylsilyl)anilines 8, were easily controlled by varying the amounts of 1 and reaction temperature as well as adding dibenzothiophene (DBTP). Reaction of 2-arylnitrobenzenes with 1 resulted in the formation of the corresponding carbazoles 14 via in situ-gen-erated phenylnitrene species derived by thermolysis of N,O-bis(trimethylsilyl)phenylhydroxylamines 7, followed by their subsequent intramolecular C H insertion. In addition, the intramolecular N N coupling reaction proceeded in the reduction of 2,2’-dinitrobiphenyl derivatives by 1, giving the corresponding benzo[c]cinnolines.

Investigations of a novel process to the framework of benzo[c]cinnoline

A novel synthetic process leading to the framework of benzo[c]cinnoline has been discovered and investigated. The process is composed of two separate reactions, the first of which is a partial reduction of the nitro groups of the 2,2′-dinitrobiphenyl, a process that we believe proceeds via a SET mechanism to yield the hydroxyamino and nitroso groups. In the following step the cyclization takes place under formation of the -N=N- bond. We believe that this process take place via a radical mechanism through the nitroso radical anion. The novel process affords either benzo[c]cinnoline or benzo[c]cinnoline N-oxide, both in high yields, 93% and 91%, respectively. To obtain benzo[c]cinnoline, the reaction is conducted with an alcohol as solvent and an alkoxide as the base, while for benzo[c]cinnoline N-oxide, water is used as solvent with sodium hydroxide as the base. To establish the latter procedure, statistical experimental design and multivariate modeling were utilized to reveal the response surface for the reaction and to determine the optimal conditions for the reaction. A proposal for the complex reaction mechanism is given. During the corroboration of the mechanism, a new deoxygenation reaction for converting benzo[c]cinnoline N-oxide into benzo[c]cinnoline was discovered. The reaction is conducted by treating the N-oxide with sodium ethoxide at elevated temperature to achieve near-quantitative conversion into benzo[c]cinnoline in a yield of 96%.

The role of ate complexes in the lithium-sulfur, lithium-selenium and lithium-tellurium exchange reactions

Hypervalent ate complexes are presumptive intermediates in the metal-halogen, metal-tellurium, and related exchange reactions. The effect of o,o′-biphenyldiyl vs. diphenyl substitution on formation of tellurium ate complexes was studied by a kinetic technique and by NMR spectroscopy. Only a modest increase in the association constant (Kate) was measured. When Li/M exchanges of o,o′-biphenyldiyl sulfides and selenides were made intramolecular by means of a m-terphenyl framework (12-S, 12-Se, 21), enormous increases (> 109) in the rate of Li/S and Li/Se exchange were observed compared to acyclic models. Apparently, these systems are ideally preorganized to favor the T-shaped geometry of the hypervalent intermediates. For the selenium systems, ate complex intermediates (20-Se, 26) were detected spectroscopically in THF- or THF/HMPA-containing solutions. A DNMR study showed that Li/Se exchange was substantially faster than exchange of the lithium reagents with the ate complex. Therefore, these ate complexes are not on the actual Li/Se exchange pathway.

Radical Cations and Anions of Benzocinnolines: An Electron Spin Resonance Study

The radical cations of benzocinnoline and its four symmetrical dimethyl derivatives have been prepared by exposure of the parent compounds as dilute solutions in CFCl3 to 60Co γ-rays at 77 K.The e.s.r. spectra were all characterised by large hyperfine coupling to two equivalent nitrogen atoms.Analysis of the data gave ca. 9percent 2s and 44percent 2p character on each nitrogen, thereby establishing a ?-structure.Clear deviation from axial symmetry shows that the orbital axes are tilted with respect to each other, an estimate of the angle between the two principle directions being ca. 40 deg.This accords reasonably well with that derived from the p:s ratio of 4.9.The estimated total spin-density on nitrogen is 1.06, showing that the SOMO is strongly localised.Similar treatment of the 2,9- and 3,8-dimethoxy derivatives gave a broad unresolved singlet.This establishes that the SOMO has switched from the ?-(N)-orbital to a ?-orbital.Clearly this has very low spin-density on the two nitrogen atoms.We were not able to detect any of the radical cations in the liquid phase.Exposure of dilute solutions of all six compounds as dilute solutions in CD3OD gave parallel features characteristic of two equivalent 14N nuclei.The perpendicular splittings were close to zero, thus confirming that the SOMO is ?, the estimated spin-density on the two nitrogen atoms being ca. 34percent each.These anions were also prepared in liquid dimethoxyethane and hexamethylphosphoric triamide, and their e.s.r. and ENDOR spectra were recorded.Relative signs of the 1H coupling constants were obtained using general triple resonance.This has led to full assignments in all cases.Our assignment for the anion of the parent compound differs from that previously proposed.