Pyridine-lV-oxides

The preferential N-nitration of pyridine would seem to indicate that direct electrophilic C-nitration is difficult to achieve expect in sterically crowded systems and when the nonbonded nitrogen electron pair is occupied such as is the case in pyridine-lV-oxides which are readily nitrated in the 4 position. Pyridinium salts have deactivated rings and are nitrated only with difficulty in the 3 position. 

V-Nitroamino)pyridine IV-oxide (lV-Nitro-4-pyridinamine 1-oxide)... 

IV.N.lV. -tetramethyl-, compd. with tantalum sulfide (TaS2). 30 164 ]34340-8I-3). 4,4 -Bipyridine, compd. with tantalum sulfide (TaS2). 30 164 [34340-84-6], Pyridine. 1-oxide, compd. with tantalum sulfide (TaS2). 30 164 [34340-85-7], Cesium hydroxide (Cs(OH)), compd. with tantalum sulfide (TaSi). 30 164... 

Chloro-2-(lV-methylhydrazino)quinoxaline 4-oxide (295) gave ethyl 7-chloro-1 -methyl-17/-[ 1,3,4Joxudiuzino 5,6- >Jquinoxuline-3-carboxylate (296) (Et02-CCOC1, pyridine, CHCI3, 5°C —> reflux, 2 h 81% mechanism discussed).500... 

You are hardly likely to understand the rationale behind this reaction from that diagram so let s explore tire details. The product of tire reaction is actually the dilrydropyridine, which has to be oxidized to the pyridine by a reagent such as HNO3, Ce(lV), or a quinone. 

From Stemmadenia donnell-smithii, besides iboga alkaloids and voac-amine, the indole (+ )-quebrachamine (L), mp 147°—149°, [a]D +111° (CHCI3), and the indole stemmadenine (LIV, a— x or a— y bond), mp 199°-200° (dec.), [ ]D + 324° (pyridine), were isolated (11). The latter alkaloid also occurs in Diplorrhynchus condylocarpon (43) along with condylocarpine, shown (43a), to be LV (rather than LVI), and into which it was converted by potassium permanganate oxidation (44). Stem-... 

The reaction of N,lV-dimethyIaniline with pyridine (equation 55) should also be considered in this category. Enamines usually attack acylated N- oxides at position 2 unless it is blocked, as in 2-methylquinoline 1-oxide, when attack takes place at C-4. Methyl /3-aminocrotonate attacks quinoline and isoquinoline TV-oxides at the position a to the N- oxide function in the presence of tosyl chloride (78JHC1425). However, pyridine and 2-methylpyridine 1-oxides react at the 4-position (equation 142). A low yield of by-product (242) is formed in each case, probably as a result of self-condensation of methyl /3-aminocrotonate. 4-Hydroxyquinoline 1-oxide is exceptional in that it reacts with an enamine in the presence of tosyl chloride at the /3-position (Scheme 170) (B-71MI20500). 5-Amino-3-methylisoxazole reacts with quinoline 1-oxide at the a-position, and the product can be degraded, to afford ultimately 2-methylquinoline (Scheme 171) (78CPB2759). 

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