Deoxygenation reactions

Nucleophilic substitution occurs in positions a and y to the N-oxide group. In nearly all these reactions deoxygenation occurs giving the substituted heterocychc amine. 

In a reaction related to azide carbonylation, aromatic nitroso compounds also give isocyanates (equation 94). [Rh2Cl2(CO)4] (96), [RhCl(CO)2py], [RhCl(CO)(PPh3)2] (71) and [RhCl(CO)-(P(OPh)3 2] all catalyzed the reaction. Deoxygenation of the nitrosobenzene derivative was the rate determining step.448 Nitrosomethane can be similarly carbonylated.449-451... 

The reactivity of substituents attached to ring nitrogens was only briefly discussed in CHEC-I because it was considered in most cases to be similar to that of carbon linked substituents <84CHEC-i(3B)i>. The most important reaction, deoxygenation of V-oxides, was summarized many methods are successful but the reagent must be selected to minimize side reactions, such as reductive dehalogenation. 

It may be noted that pyrolysis of isoindoline (V-oxides may also furnish isoindoles,32 although in general this is a less useful preparative route since other reactions (deoxygenation, Cope elimination of the 2-substituent) may intervene,6 as shown for the 2-(/J-phenylethyl) derivative in Scheme 2. 

Reductive carbonylation of nitro compounds is catalyzed by various Pd catalysts. Phenyl isocyanate (93) is produced by the PdCl2-catalyzed reductive carbonylation (deoxygenation) of nitrobenzene with CO, probably via nitrene formation. Extensive studies have been carried out to develop the phosgene-free commercial process for phenyl isocyanate production from nitroben-zene[76]. Effects of various additives such as phenanthroline have been stu-died[77-79]. The co-catalysts of montmorillonite-bipyridylpalladium acetate and Ru3(CO) 2 are used for the reductive carbonylation oLnitroarenes[80,81]. Extensive studies on the reaction in alcohol to form the A -phenylurethane 94 have also been carried out[82-87]. Reaction of nitrobenzene with CO in the presence of aniline affords diphenylurea (95)[88]. 

As another example of nitrene formation, the reaction of o-nitrostilbene (96) with CO in the presence of SnCU affords 2-phenylindole (97). The reaction is explained by nitrene formation by deoxygenation of the nitro group with CO, followed by the addition of the nitrene to alkene. Similarly, the 2//-indazole derivative 99 was prepared by reductive cyclization of the A-(2-nitrobenzyli-dene)amine 98[89]. 

Iron hahdes react with haHde salts to afford anionic haHde complexes. Because kon(III) is a hard acid, the complexes that it forms are most stable with F and decrease ki both coordination number and stabiHty with heavier haHdes. No stable F complexes are known. [FeF (H20)] is the predominant kon fluoride species ki aqueous solution. The [FeF ] ion can be prepared ki fused salts. Whereas six-coordinate [FeCy is known, four-coordinate complexes are favored for chloride. Salts of tetrahedral [FeCfy] can be isolated if large cations such as tetraphenfyarsonium or tetra alkylammonium are used. [FeBrJ is known but is thermally unstable and disproportionates to kon(II) and bromine. Complex anions of kon(II) hahdes are less common. [FeCfy] has been obtained from FeCfy by reaction with alkaH metal chlorides ki the melt or with tetraethyl ammonium chloride ki deoxygenated ethanol. 

In the pyrolysis of pure amine oxides, temperature has a significant effect on the ratio of products obtained (22). The principal reaction during thermal decomposition of /V,/V-dimetby11 amyl amine oxide [1643-20-5] at 80—100°C is deoxygenation to /V,/V-dimetby11 amyl amine [112-18-5] (lauryl = dodecyl). 

Reduction. Just as aromatic amine oxides are resistant to the foregoing decomposition reactions, they are more resistant than ahphatic amine oxides to reduction. Ahphatic amine oxides are readily reduced to tertiary amines by sulfurous acid at room temperature in contrast, few aromatic amine oxides can be reduced under these conditions. The ahphatic amine oxides can also be reduced by catalytic hydrogenation (27), with 2inc in acid, or with staimous chloride (28). For the aromatic amine oxides, catalytic hydrogenation with Raney nickel is a fairly general means of deoxygenation (29). Iron in acetic acid (30), phosphoms trichloride (31), and titanium trichloride (32) are also widely used systems for deoxygenation of aromatic amine oxides. 

Other 2,3-Diphosphoglycerate Pocket Cross-Linkers. The reactivity of the valine NAl(l)a and lysine EF6(82)p residues in the 2,3-DPG pocket shown by NFPLP and (bis-PL)P4 has stimulated the search for other reagents that react similarly but have potential for greater efficiency and ease of scaleup. The systematic study of four different dicarboxyhc acid derivatives, cross-linked in both oxygenated and deoxygenated conditions, has been reported (92). Each of these derivatives presents problems in purification, and proof of the sites of reaction is tedious. 

The standard reduction potential of Cr " (Table 2) shows that this ion is a strong reducing agent, and Cr(II) compounds have been used as reagents in analytical chemistry procedures (26). The reduction potential also explains why Cr(II) compounds are unstable in aqueous solutions. In the presence of air, the oxidation to Cr(III) occurs by reaction with oxygen. However, Cr(II) also reacts with water in deoxygenated solutions, depending on acidity and the anion present, to produce H2 and Cr(III) (27,28). 

Oxepin, 4-ethoxycarbonyl-2,3,6,7-tetrahydro-synthesis, 7, 578 Oxepin, 2-methyl-enthalpy of isomerization, 7, 555 Oxepin, 2,3,4,5-tetrahydro-reduction, 7, 563 synthesis, 7, 578 Oxepin, 2,3,4,7-tetrahydro-synthesis, 7, 578 Oxepin, 2,3,6,7-tetrahydro-oxidation, 7, 563 reduction, 7, 563 Oxepin-2,6-dicarboxylic acid stability, 7, 565 Oxepinium ions synthesis, 7, 559 Oxepins, 7, 547-592 antiaromaticity, 4, 535 applications, 7, 590-591 aromatization, 7, 566 bond lengths and angles, 7, 550, 551 cycloaddition reactions, 7, 27, 569 deoxygenation, 7, 570 dipole moment, 7, 553 disubstituted synthesis, 7, 584... 

N-alkylation, 4, 236 Pyrrole, 2-formyl-3,4-diiodo-synthesis, 4, 216 Pyrrole, 2-formyl-1-methyl-conformation, 4, 193 Pyrrole, 2-formyl-5-nitro-conformation, 4, 193 Pyrrole, furyl-rotamers, 4, 546 Pyrrole, 2-(2-furyl)-conformation, 4, 32 Pyrrole, 2-halo-reactions, 4, 78 Pyrrole, 3-halo-reactions, 4, 78 Pyrrole, 2-halomethyl-nucleophilic substitution, 4, 274 reactions, 4, 275 Pyrrole, hydroxy-synthesis, 4, 97 Pyrrole, 1-hydroxy-cycloaddition reactions, 4, 303 deoxygenation, 4, 304 synthesis, 4, 126, 363 tautomerism, 4, 35, 197 Pyrrole, 2-hydroxy-reactions, 4, 76 tautomerism, 4, 36, 198... 

The synthetic procedure described is based on that reported earlier for the synthesis on a smaller scale of anthracene, benz[a]anthracene, chrysene, dibenz[a,c]anthracene, and phenanthrene in excellent yields from the corresponding quinones. Although reduction of quinones with HI and phosphorus was described in the older literature, relatively drastic conditions were employed and mixtures of polyhydrogenated derivatives were the principal products. The relatively milder experimental procedure employed herein appears generally applicable to the reduction of both ortho- and para-quinones directly to the fully aromatic polycyclic arenes. The method is apparently inapplicable to quinones having an olefinic bond, such as o-naphthoquinone, since an analogous reaction of the latter provides a product of undetermined structure (unpublished result). As shown previously, phenols and hydro-quinones, implicated as intermediates in the reduction of quinones by HI, can also be smoothly deoxygenated to fully aromatic polycyclic arenes under conditions similar to those described herein. 

The duration of these reactions appears to be extremely important as longer reaction times resulted in deoxygenation of the thiophene derivative. 

---