Studies on Quinoxaline N-Oxides. I

Hayashi, Eisaku; Iijima, Chihoko

doi:10.1248/yakushi1947.82.8_1093

Cited by 32 publications

(10 citation statements)

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“…A variety of methods involving metals have been developed for the N -oxide to amine conversion. 2–21 There are fewer methods that do not rely on the use of metals, such as processes involving sulfurous acid, 22 SO 2 , 23 sulfur monoxide, 24 trimethyl(ethyl)amine–SO 2 complex, 25 PCl 3 , 26 PPh 3 at high temperatures, 27 di- n -propyl sulfoxylate, 28 CS 2 , 29 bakers’ yeast, 30 and alcohols and a base. 31 …”

Section: Introductionmentioning

confidence: 99%

Reduction of Amine N-Oxides by Diboron Reagents

et al. 2011

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Facile reduction of alkylamino-, anilino-, and pyridyl-N-oxides can be achieved via the use of diboron reagents, predominantly bis(pinacolato)- and in some cases bis(catecholato)diboron [(pinB)2 and (catB)2, respectively]. Reductions occur upon simply mixing the amine N-oxide and the diboron reagent in a suitable solvent, at a suitable temperature. Extremely fast reductions of alkylamino- and anilino-N-oxides occur, whereas pyridyl-N-oxides undergo slower reduction. The reaction is tolerant of a variety of functionalities such as hydroxyl, thiol, and cyano groups, as well as halogens. Notably, a sensitive nucleoside N-oxide has also been reduced efficiently. The different rates with which alkylamino- and pyridyl-N-oxides are reduced has been used to perform stepwise reduction of the N,N’-dioxide of (S)-(–)-nicotine. Because it was observed that (pinB)2 was unaffected by the water of hydration in amine oxides, the feasibility of using water as solvent was evaluated. These reactions also proceeded exceptionally well, giving high product yields. In constrast to the reactions with (pinB)2, triethylborane reduced alkylamino-N-oxides, but pyridine N-oxide did not undergo efficient reduction even at elevated temperature. Finally, the mechanism of the reductive process by (pinB)2 has been probed by 1H and 11B NMR.

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Section: Introductionmentioning

confidence: 99%

Reduction of Amine N-Oxides by Diboron Reagents

et al. 2011

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“…12 2,3-Dimethylquinoxaline can be oxidized with peracetic acid in acetic acid to a mono-or di-N-oxide by appropriate choice of reaction condit i o n~.~~ 1,4-Dioxides have also been prepared with this reagent from other 2,3-dialkylquinoxalines, but similar treatment of 2-isopropyl-3-methylquinoxaline gives a considerable proportion of the 4-oxide, and 2,3-diisopropylquinoxaline is unchanged by hot peracetic or performic acids.13 2,3-Diphenylquinoxaline is converted by peracetic acid into a mixture of the 1-oxide and 1,4-dioxide; however with excess of aqueous hydrogen peroxide in acetic acid, in addition to the 1,4-dioxide, N,N'dibenzoyl-o-phenylenediamine is also formed.14 The results of oxidizing other 2,3-disubstituted quinoxalines are broadly predictable from what is known about the oxidation of the monosubstituted compounds. 12 2,3-Dimethylquinoxaline can be oxidized with peracetic acid in acetic acid to a mono-or di-N-oxide by appropriate choice of reaction condit i o n~.~~ 1,4-Dioxides have also been prepared with this reagent from other 2,3-dialkylquinoxalines, but similar treatment of 2-isopropyl-3-methylquinoxaline gives a considerable proportion of the 4-oxide, and 2,3-diisopropylquinoxaline is unchanged by hot peracetic or performic acids.13 2,3-Diphenylquinoxaline is converted by peracetic acid into a mixture of the 1-oxide and 1,4-dioxide; however with excess of aqueous hydrogen peroxide in acetic acid, in addition to the 1,4-dioxide, N,N'dibenzoyl-o-phenylenediamine is also formed.14 The results of oxidizing other 2,3-disubstituted quinoxalines are broadly predictable from what is known about the oxidation of the monosubstituted compounds.…”

Section: N-oxidation Of Quinoxalinesmentioning

confidence: 99%

Quinoxaline Mono‐ and Di‐ N ‐Oxides

1979

Chemistry of Heterocyclic Compounds: A Series of Monographs

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“…The reagent combination employed for this transformation is polymethylhydrosiloxane (PMHS) in the presence of either tetrakis (triphenylphosphine) palladium (0) [Pd(PPh 3 ) 4 ], titanium (IV) isopropoxide [Ti(i-PrO) 4 ] or palladium on carbon (Pd/C).Amine N-oxides have attracted the attention of synthetic organic chemists due to their differential chemical behavior as compared to their parent amines. It is well documented that hetero aromatic amine N-oxides behave differently in regioselectivity.…”

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confidence: 99%

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confidence: 99%

“…However the combination was not selective for substrates containing olefin, nitro and other reducible groups. Thus several catalysts were tested for activating PMHS which is otherwise inert and we found titanium (IV) isopropoxide [Ti(i-PrO) 4 ] and tetrakis (triphenylphosphine) palladium (0) [Pd(PPh 3 ) 4 ] are also to be very useful ones. Accordingly, the same pyridine N-oxide 1a was subjected to PMHS in presence of both the catalysts to give pyridine 2a in 85-88% yield.…”

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Efficient and Chemoselective Deoxygenation of Amine N-Oxides Using Polymethylhydrosiloxane

Chandrasekhar¹,

Reddy²,

Rao³

et al. 2002

Synlett

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Deoxygenation of aromatic and aliphatic amine N-oxides to the corresponding amines is achieved under mild conditions. The reagent combination employed for this transformation is polymethylhydrosiloxane (PMHS) in the presence of either tetrakis (triphenylphosphine) palladium (0) [Pd(PPh 3 ) 4 ], titanium (IV) isopropoxide [Ti(i-PrO) 4 ] or palladium on carbon (Pd/C).Amine N-oxides have attracted the attention of synthetic organic chemists due to their differential chemical behavior as compared to their parent amines. It is well documented that hetero aromatic amine N-oxides behave differently in regioselectivity. 2 Thus oxidation of amines to amine N-oxides and reverting back to the parent amine constitutes a useful transformation set (Scheme). This latter transformation is complex for which several reagents have been developed. Aromatic N-oxides are relatively more stable than aliphatic ones and are resistant to deoxygenation, 3 although some of them undergo deoxygenation with sulfurous acid. 4 Traditionally deoxygenation has been carried out with complex hydrides, 5 trivalent phosphorus compounds, 6 various sulfur and selenium compounds, 7 dissolved metals, 8 iron, 9 titanium trichloride in aqueous solution, 10 titanium tetrachloride in the presence of zinc or magnesium 11 or catalytic hydrogenation. 12 These deoxygenations however require relatively drastic reaction conditions. Some of the reagents used for selective deoxygenation include trialkyl amine-sulfur dioxide complexes, 13 aluminium iodide, 14 acetic formic anhydride, 15 ammonium formate-palladium on carbon, 16 sodium hydrogen telluride, 17 chromium(II)chloride, 18 low valent titanium, 19 sodium borohydride 20 and SmI 2 . 21 Recently titanocene methylidene complex derived from Tebbe and Petasis reagent, 22 triphenyl phosphene-oxorhenium (V) catalyst, 23 In/aq. NH 4 Cl, 24 and Zn/aq. NH 4 Cl 25 mediated deoxygenations of amine N-oxides have been reported. Some of these are associated with limitations regarding selectivity and/or incompatibility with other functional groups and are expensive, hazardous and/or sensitive to both air and moisture. We have been exploring the utility of polymethylhydrosiloxane (PMHS) as an efficient reduction reagent 26 besides others. 27 It was expected that the N-oxide class of compounds would also reduce back to parent amines in presence of PMHS based on the literature precedence. 12,16 To make this expectation a reality, the easily accessible pyridine N-oxide 1a (entry 1, Table 1) was subjected to polymethylhydrosiloxane in the presence of Pd/C activator and formation of pyridine 2a was observed in 90% yield. However the combination was not selective for substrates containing olefin, nitro and other reducible groups. Thus several catalysts were tested for activating PMHS which is otherwise inert and we found titanium (IV) isopropoxide [Ti(i-PrO) 4 ] and tetrakis (triphenylphosphine) palladium (0) [Pd(PPh 3 ) 4 ] are also to be very useful ones. Accordingly, the same pyridine N-oxide 1a was subjected to PMHS in presence ...

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Studies on Quinoxaline N-Oxides. I

Cited by 32 publications

References 0 publications

Reduction of Amine N-Oxides by Diboron Reagents

Reduction of Amine N-Oxides by Diboron Reagents

Quinoxaline Mono‐ and Di‐ N ‐Oxides

Efficient and Chemoselective Deoxygenation of Amine N-Oxides Using Polymethylhydrosiloxane

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