Pyrido pyrazine oxidation

Pyrido[2,3-6]pyrazine, 8-hydroxy-tautomerism, 3, 250 Pyrido[2,3-h]pyrazine, methyl-acylation, 3, 253 Pyrido[2,3-6]pyrazine, 2-oxo-oxidation, 3, 250-251... 

Ring transformation of pyrido[2,3-f]furoxan 676 with 1,3-diketones or /3-keto esters was catalyzed by silica gel, alumina, or molecular sieves to give mainly the corresponding pyrido[2,3- ]pyrazine 1,4-dioxides 677 in addition to pyrido[2,3- ]pyrazine 1-oxides 678 in a low yield (Equation 57) <1997H(45)107>. 

Oxidation of 3-hydroxymethyl-2,3-dihydro-5H-pyrido[l,2,3-cfe][1,4] benzoxazin-5-ones with o-iodoxybenzoic acid in DMSO and with Dess-Martin periodinate in CH2CI2 afforded 3-formyl derivatives (08WOP2008/ 120003). Dehydrogenation of ethyl 10-[2-(ferf-butoxycarbonyl)-l,2,3,4,6,8a-hexahydropyrrolo[l,2-a]pyrazin-7-yl]-9-fluoro-3(S)-methyl-7-oxo-2,3-dihydro-7H-pyrido[l,2,3-de][l,4]oxazine-6-carboxylates in the presence of Pd/C with air in MeOH afforded 10-[2-(ferf-butoxycarbonyl)-l, 2,3,4-tetrahydropyrrolo[l,2-a]pyrazin-7-yl] derivatives, which then were deprotected (09BML4933). 

Hydrogenation of 2-bromopyrido[l,2-n]pyrazin-5-ium bromide and its 2-oxide over Pt02 gave pyrido[l,2-a]pyrazin-5-ium bromide and its 2-oxide [67JCS(C)2391], Reduction of 7-oxo-2-(2-pyrimidinyl)perhydropyrido[l,2-a]pyrazine with 10% NaBH4 on alumina in MeOH afforded 7-hydroxy derivative (96MIP4). 

Hexahydro-l//-pyrido[l,2-a]pyrazin-l-ones were prepared by oxidation of 2-substituted perhydropyrido[l,2-a]pyrazines and perhydro-pyrido[l,2-a]pyrazin-l-one with Hg(OAc)2 in 5% aqueous AcOH (73CPB1248). Oxidation of l,3,4,6,ll,lla-hexahydro-2//-pyrazino[l,2-bjisoquinoline with Hg(OAc)2 in 5% aqueous AcOH gave the 6-oxo derivative [73CPB2039 77IJC(B)70]. l,3,4,6,ll,lla-Hexahydro-2//-... 

Little is known about the chemistry of pyridylfuroxans, but reaction of the [l,2,5]oxadiazolo[3,4-Z>]pyridine oxides (126) and (127) with activated methylene synthons provides pyrido[2,3-6]pyrazine-1,4-dioxides (130) in moderate yields (Beirut reaction) (Table 4, Scheme 21) <80M407, 82AF10). The actual reactive species is presumed to be the bis(nitroso)pyridine isomer (128). Direct oxidation... 

The cyclization of ethyl 4-amino-5-[(cyanophenylrnethyl)amino]-6-[(diphenylmethyl)amino]-2-pyridyl carbamate (13) by methanolic sodium methoxide and subsequent air oxidation gives ethyl 8-amino-4-(diphenylmethyl)-3-imino-2-phenylpyrido[2,3-6]pyruzin-6-yl J-carbarn ate (14), together with ethyl 2-amino-5-[(diphenylmethyl)amino]-3-phenylpyrido[3,4-Z>]pyrazin-7-yl carbamate (cf. pyrido[3,4-6]pyrazines, Section 7.2.3.2.1.1.2.) in low yield.15... 

Partially hydrogenated pyrazine moieties in pyrido[2,3-6]pyrazines are aromatized by permanganate11,67 or iodine.7 Thus, ethyl 8-amino-3,4-dihydro-2-methylpyrido[2,3-6]pyrazine-6-carba-mate (1) with potassium permanganate in acetone yields 84% of the fully aromatic compound 2,11 another example being the oxidation of l,2,3,4-tetrahydro-2,3-dimethylpyrido[2,3-A]pyrazine (3)-67 nh2 nh2... 

Dihydropyrido[2,3-6]pyrazin-2(l//)-one (4) is aromatized by iodine in aqueous potassium iodide solution to give pyrido[2,3-6]pyrazin-2(l//)-one (5), whereas potassium hcxacyanofer-rate(III) will oxidize further to pyrido[2,3-6]pyrazine-2,3(l//,4//)-dione (fry1... 

Pyndo[2,3-()]pyrazines with a partially hydrogenated pyridine moiety have also been aromatized. 7,8-Dihydro-7-methylpyrido 2,3-6]pyrazin-6(5//)-one (7) oxidized by selenium dioxide in acetic acid affords 7-methyl pyrido[2,3-A]pyrazin-6(5//)-one (8),63 and 5,6-dihydro-5-methylpyrido-[2,3-6]pyrazine (9) is oxidized by air to give 5-methylpyrido[2,3-6]pyrazin-6(5//)-one (10).14... 

Oxidation of pyrido[2.3-i]pyrazine (1) by a variety of pcracids (peracetic, monoperoxyphthalic, or 4-nitroperoxybenzoic acid),67 or hydrogen peroxide in sulfuric acid7 results in the formation of pyrido[2,3-%>yrazin-6(5//)-one (2). 

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