2-Methylpyridine N-oxide

Epoxides such as cyclohexene epoxide are converted by MesSiSiMes 857/12 or TMS 14/NaI, via O-silylated-2-iodocyclohexanol 1777 [26], into cyclohexene [27, 28] (cf also Ref. [33]). Pyridine-N-oxides such as 2-, 3-, or 4-methylpyridine-N-oxides 1778 are reduced by Me3SiI 17/Zn in acetonitrile, probably via 2-iodopyridines 1779, to picolines in 80-92% yield [29] (Scheme 12.8). 

Conductivity studies have been carried out for the salt of (NPCl2)3 and 4-methylpyridine N-oxide, i.e. (NPC s NPCl(0-NC5H4Me-4)] Cl," and for the hexa(azophenol) derivatives of cyclotriphosphazene. 

Reaction of pyridine N-oxide 860 with excess allyltrimethylsilane 82 affords, via 947, 2-propenylpyridine 948 in 53% yield as the only reaction product which can be isolated. Ehmination of trimethylsilanol 4 from 947 is apparently followed by fluoride-catalyzed isomerization of 2-allylpyridine into 2-propenylpyridine 948. 3-Methylpyridine-N-oxide 867 a is converted into 2-propenyl-3-methylpyridine in 69% yield. Likewise, fluoride-catalyzed addition of excess benzyltrimethylsilane 83 to 860 furnishes, via 949, 2-benzylpyridine 950 in 70% yield. The generated leaving group trimethylsilanol 4 reacts with excess allyltrimethylsilane 82 or benzyltrimethylsilane 83 in the presence of fluoride to give hexamethyldisiloxane (HMDSO) 7 and propylene or toluene, respectively [60] (Scheme 7.16). 

Winkler S, Ockels W, Budzikiewicz H, Korth H, Pulverer G (1986) 2-Hydroxy-4-methoxy-5-methylpyridin-N-oxid, ein Al -bindender Metabolit von Pseudomonas cepacia. Z Naturforsch 41c 807... 

Salts of [ZnLe]2+ (L = pyridine N-oxide) have recently been shown to undergo facile solid state reactions with alkali metal halides, an observation to be taken into account when recording the IR spectra of these and related compounds.706 A crystal structure of the complex [ZnL6] [C104]2 (L = 4-methylpyridine A-oxide) has been reported.707 The metal is in a near-octahedral 06 environment, with an average Zn—O distance of 2.114 A. 

L = Dihexylsulfoxides trimethylamine l,eu-diaminoalkane(n = 2-4) l,2-bis-(dimethylamino)ethane. tet a lethylpiperid ne pyridine, 4-methyIpyridine 2-methylpyridinc, pyridine 1-oxide 2-, 3-. and 4-methylpyridine 1-oxides triphenylphosphane triphenylphosphane oxide, sulfide, and selenidc " tributylphosphane selenide , tris[4-methoxyphenyl]phosphane selenide, 1,2-bis(diphenylphosphano)ethane f -diselenide, thiourea, letramethylthiourea, dithioxamide dimethylacetamide ... 

There are numerous investigations of the reactivity of di- and polyhalo-pyridazines, particularly polyfluoropyridazines. Aminolysis of l-phenyl-4,5-dichloropyridazin-6-one has been studied in detail. In this and other reactions with nucleophiles, the halogen atom at position 4 is substituted preferentially, although a mixture of 4-amino and 5-amino derivatives is formed in the reaction between 4,5-dihalopyridazin-6-ones and ammonia or amines. It has been now firmly established that displacement reactions on 3,6-dichloropyridazine 1-oxide with sulfur nucleophiles take place at position 6 in contrast to nitrogen or oxygen nucleophiles, where the 3-chlorine atom is replaced preferentially. In connection with the previously observed self-condensation of 3-chloro-6-methylpyridazine to a tricyclic product, the reaction between 3,6-dichloropyridazine and pyridine N-oxides was investigated. 3,6-Dichloropyridazine with 2-methylpyridine N-oxide at 100°-110°C affords three compounds (171, 172, and 173). With 2,6-dimethylpyridine N-oxide, an ether (174) is also formed. The isolation of... 

Cyanation of 3-methoxymethyl-2-methylpyridine N-oxide (674) gave the 4-cyano derivative 675 in 20% yield which, with methylmagnesium... 

X-oxocarboxylic acids. Both aryl and alkyl a-oxocarboxylic acids reacted under these conditions. The pyridine N-oxides could have a number of substituents at C-4 including Cl, Me, CN, and OMe. Additionally, quinoline N-oxides reacted under these conditions. 2-Methylpyridine N-oxide and 3-iodopyridine N-oxide were acylated at both C-4 and C-2 in nearly equal amounts. This indicates that the mechanism may not occur by straightforward C-H activation (14RSC Advances31685). 

C7HsNOa, Pyridine-2,3-dicarboxylic acid, 39B, 175 40B, 222 C7H5NO5, 2,6-Dicarboxypyridine N-oxide, 43B, 293 C7H7CI2NO, 3,5-Dichloro-2,6-dimethyl-4-pyridinol, 38B, 260 C7H7NO3, 2-Carboxy-6-methylpyridine N-oxide, 41B, 277 C7H7NO5, Dipicolinic acid monohydrate, 39B, 176 C7H8CINO, 2-Acetylpyridine hydrochloride, 31B, 123... 

KOH dissolved in a mixture of n-propylmercaptan and dimethylformamide, added dropwise during 1 hr. to a vigorously stirred suspension of 4-nilro.-2-methylpyridine N-oxide in dimethylformamide, heated 1 hr. on a water bath, the crude product dissolved in glacial acetic acid, and treated with Fe-powder -> 4-n-propylthio-2-methylpyridine. Y 81%. Also via chlorides s. E. Profft and W.Rolle, J. pr. 11, 22 (I960). 

For Negishi reactions in which the pyridines are nucleophiles, the pyridylzinc reagents are usually prepared from the corresponding halopyridines [6, 20, 21]. An excess of 2-chlorozincpyridine /V-oxide (26), arising from 2-bromopyridine N-oxide hydrochloride (25), was coupled with vinyl triflate 27 in the presence of Pd(Ph3p)4 to furnish adduct 28 [20]. Recently, an efficient Pd-catalyzed cyanation of 2-amino-5-bromo-6-methylpyridine (29) using zinc cyanide has been reported to afford pyridyl nitrile 30 [22]. 

The reaction of N,N- dimethylaniline 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 AT-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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