Arene oxides deoxygenation

Transition-metal complexes such as [Rh(CO)2Cl]2,204 Rh(butadiene)2Cl,205 or Cr(CO)3(NH3)312 have also been used for the deoxygenation of oxepins to give 312,204 205 and benzoxepins to give 4.12,204 Occasionally, substantial amounts of phenolic compounds have been isolated due to the competing NIH shift of the arene oxide.204 1-Benzoxepin and 3-benzoxepin resist oxygen extrusion under these conditions probably due to their inability to form arene oxi-des.133,204... 

The deoxygenation of arene oxides have also been achieved by using chromium carbonyl complexes. The aromatic hydrocarbons produced are partially converted to chromium complexes. Formation of 246 in methanol suggests Rh-catalyzed solvolysis, resulting in nucleophilic addition of meth-... 

Arene oxides show the characteristic reactions of epoxides (isomerization to ketones, reductions to alcohols, nucleophilic additions, deoxygenations) and olefins or conjugated dienes (catalytic hydrogenation, photochemical isomerization, cycloaddition, epoxidation, metal complexation). Where a spontaneous, rapid equilibration between the arene oxide and oxepin forms exists, reactivity typical of a conjugated triene is also found. 

Pyridine is also capable of deoxygenating arene oxides 110 and 112. The deoxygenation of benzene oxides in the presence of iron, chromium, and rhodium catalysts has been studied, and a mechanism for the reduction process has been proposed. Deoxygenation of K-region arene oxides is also catalyzed... 

Deoxygenation of the readily available oxanorbornadienes (106 R = COjMe, = H, Me) with [Rh(CO)2Cl]2 yields the benzazepines (107) in modest yields <82CB2I25>. Light-induced valence tautomerization of (106) followed by thermal rearrangement affords the arene oxide (108), which leads to the benzazepine (109) on deoxygenation, a process which may be regarded as a 1-3 transposition of the nitrogen atom (Scheme 18). 

Well-defined arene complexes of Group 4 metals in various oxidation states have been isolated. The air- and moisture-sensitive complexes Ti(r -arene)2 (56) have a sandwich structure similar to that of the related chromium compounds [176-178]. They have been used for deoxygenation of propylene oxide and coupling reaction of organic carbonyl compounds [179]. The first synthesis of 56 was cocondensation of metal vapor with arene matrix [176]. Two more convenient methods are reduction of TiCl4 with K[BEt3H] in arene solvent [180] and reaction of TiCl4(THF)2 with arene anions followed by treatment with iodine [170,176]. The latter method involves the formation of an anionic titanate complex, [Ti(ri -arene)2] (57), which can also be formed from KH and 56 [181]. 

In analogy to the fullerene oxidation, the arene radical cations were generated in deoxygenated DCM solutions containing ca. 2 x 10 M of the respective arenes. As a convenient means to probe the formation and the lifetime of the generated (arene)" the respective absorptions in the UV-VIS region were monitored. 

To study the electron transfer from [60]fiillerene to the arene radical cation, deoxygenated DCM solutions of, for example, m-terphenyl were irradiated in the presence of variable [60]fullerene concentrations (0.7 - 6.0) x 10 M. The short life-time of some of the (arene)", in combination with the unfavorably high ionization potential of [60]fiillerene limited the ability to measure the electron transfer process to, however, only a few (arene) . Formation of the electron transfer product, namely, was confirmed spectroscopically by measuring the NIR fingerprint at > max= 980 nm, which resembles that found upon direct oxidation of [60]fullerene. 

Photolysis of pyridine-N-oxide in the gas-phase results in deoxygenation to pyridine via a triplet excited state. On photolysis in benzene solution or in the presence of naphthalene, the N-oxide oxygen is transferred to an arene molecule, thus undergoing either C-H insertion (to give phenol) or addition to a double bond (to give an areneoxide 119) ... 

Sml2 and other lanthanoid halides are often used as stoichiometric reagents in the deoxygenation of organoheteroatom oxides [88, 97], the tandem radical cyclization [140], the transformation of carbohydrates to carbocycles [140], the alkylation and arylation of perfluorinated arenes [101]. CeCl3 is used in the aldol condensation [95] ... 

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