JV-oxidation

JV-Oxidation of phthalazine with monoperoxyphthalic acid produces the corresponding... 

Pyridazino[4,5 -c]isoquinoIine, 6-aryI-synthesis, 3, 244 Pyridazino[3,4-c]isoquinoIines alkylation, 3, 238 JV-oxide, 3, 327 synthesis, 3, 247-248 Pyridazino[4,3-c]isoquinolines synthesis, 3, 247 Pyridazino[4,5-c]isoquinolines alkylation, 3, 238 Pyridazin-3(2H)-one, 6-acryIoxy-polymers, 1, 288... 

Electronic spectral considerations were invoked by Boyer et in favor of the i/i-o-dinitroso- structure and by Mallory and Wood against an oxaziridine formulation for the jV-oxide structure. The spectra of some nitrobenzofuroxans have been reported. 

Ochiai and Ohta have used lead tetraacetate in benzene to convert aromatic iV-oxides (67) to the corresponding acetylated hydroxamic acids (68). Similar oxidation of quinoline and isoquinoline JV-oxides... 

There are no examples of monocyclic azepine JV-oxides however, cyclopent 7>]azcpine is readily oxidized by 3-chloroperoxybenzoic acid at room temperature to give the moderately stable, green, crystalline cyclopent[6]azepine 1-oxide (l).2 6,8-Dibromocyclopcnt[6]azcpinc, under similar conditions, fails to react. 

The benzodiazepine jV-oxide 4 is converted into the cyclic hydroxylamine 9 by the action of lithium aluminum hydride, while catalytic hydrogenation in the presence of platinum gives the tetrahydrobenzodiazepine 10.219... 

Reductions of Heterocyclic JV-Oxides and Aromatic Nitro Croups... 

Klemm and coworkers studied the spectra of several thienopyridine sulfones (72-78) and found that it is possible to distinguish by mass spectrometry between a sulfone function and a combination of two sulfoxide or JV-oxide functions in the same molecule . For instance, compound 77 forms 78 losing the 7V-oxygen atom, since except for the molecular ion their mass spectra are very similar. Compound 78 rearranges prior to fragmentation to the two possible cyclic sulfinates (80 and 81), which then fragment further by losing SO and CNO, respectively. 

On treatment with aerated sodium in liquid ammonia, tetrahydroproto-berberine JV-oxides (35a and 35b) afforded the C-14—N bond cleavage products 36 and 37 (Scheme 8) (37). The same trans IV-oxides also gave the C-14—N cleavage products 38 and 39 on photolysis (33). 

Scheme 73. Synthesis of protopine alkaloids from tetrahydroprotoberberine JV-oxides. Reagents a, K2Cr07 b, Mel.

The enol lactones were synthesized by Hofmann degradation of metho salts of classic phthalideisoquinoline alkaloids. The biogenetically relevant transformations were highly stereospecific. In this way aobamidine (96) was obtained from the methiodide of (erythro) bicuculline (88) (2), and ad-lumidiceine enol lactone (97) was produced from both (threo) isomeric adlumidiceine (89) and capnoidine (90) methiodides (14,15,91-93). (Z)- (98) and ( )-N-methylhydrastine (99) were obtained from / - (91, erythro) and a-N-methylhydrastinium (92, threo) iodides (5,87,91,96-98), respectively, as were (Z)- (101) and (JE)-narceine enol lactones (102) synthesized from a- (94, erythro) and /J-narcotine (95, threo) quaternary N-metho salts (87,90), respectively. In a similar process /J-hydrastine (91) JV-oxide heated in chloroform yielded enol lactone 124 of Z configuration (99) however, a-narcotine (94) N-oxide was transformed to benzoxazocine 125 (99). ... 

The iV-( -nitrophcnyl)pipcrazinc-2-carbonitrilc 251 (Y = NBOC) was reductively cyclized to the tricyclic /V-oxides 252 (Y = NBOC) either by catalytic hydrogenation, or by electrochemical reduction. Electrochemical reduction gave lower yield. Compounds 251 were prepared by electrochemical cyanation of the iV-(o-nitrophenyl)piperazine 250. The jV-oxides 252 were further hydrogenated to the 2,3,4,4 ,5,6-hexahydro-l//-pyrazino[l,2- ]quinoxaline 253 (Y = NBOC) (Scheme 46) <2001EJ0987>. 

Reaction yields and regioselectivity were comparable, or better, than those obtained with more simple nitrile oxides. Examples of the use of an optically active (R)-4-chloro-valeronitrile JV-oxide for the synthesis of non-racemic isoxa-lines 371d and 371e are also reported [93]. 

The formation of quinoxaline heterocyclic systems is a well-known transformation of benzofuroxanes, which occurs in the presence of /3-dicarbonyl compounds <2001RJ0891, 2003BMC2149, 2003EJM791, 2005JME2019>. For example, the synthesis of quinoxaline 1,4-di-jV-oxides was carried out by reaction of the appropriate benzofuroxane 69 with the corresponding /3-ketoester, using triethylamine as the catalyst (Scheme 15) <2005JME2019>. 

The thermal cyclization of 3-pyridazinylaminomethylenemalonate N-oxide (1052) by heating in diphenyl ether at 250°C for 15 min gave pyrido[2,3-c]pyridazine-6-carboxylate jV-oxide (1053) in 70% yield (72JHC351). 

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