Pyridine 1-oxide mercuration

Zinc enolate 4, prepared from acetylene ether pyridine i-oxide, mercuric chloride, and zinc, adds to aldehydes to form a-chloro-3-hydroxy esters 5 in good yields ( ). Subsequent treatment with base gives trans-epoxyesters, one of which 6 is converted to 2-amino-2-deoxy-D-ribose stereoselectively in good yields (O. 

The preferred position for electrophilic substitution in the pyridine ring is the 3 position. Because of the sluggishness of the reactions of pyridine, these are often carried out at elevated temperatures, where a free radical mechanism may be operative. If these reactions are eliminated from consideration, substitution at the 3 position is found to be general for electrophilic reactions of coordinated pyridine, except for the nitration of pyridine-N-oxide (30, 51). The mercuration of pyridine with mercuric acetate proceeds via the coordination complex and gives the anticipated product with substitution in the 3 position (72). The bromina-tion of pyridine-N-oxide in fuming sulfuric acid goes via a complex with sulfur trioxide and gives 3-bromopyridine-N-oxide as the chief product (80). In this case the coordination presumably deactivates the pyridine nucleus in the 2 and... 

Acid acceptors Lead acetate trihydrate. 2,6-Lutidine. Magnesium oxide. Mercuric oxide. Pyridine. Sodium acetate. 

IODINE (7553-56-2) A powerful oxidizer. Material or vapors react violently with reducing agents, combustible materials, alkali metals, acetylene, acetaldehyde, antimony, boron, bromine pentafluoride, bromine trifluoride, calcium hydride, cesium, cesium oxide, chlorine trifluoride, copper hydride, dipropylmercury, fluoride, francium, lithium, metal acetylides, metal carbides, nickel monoxide, nitryl fluoride, perchloryl perchlorate, polyacetylene, powdered metals, rubidium, phosphorus, sodium, sodium phosphinate, sulfur, sulfur trioxide, tetraamine, trioxygen difluoride. Forms heat- or shock-sensitive compounds with ammonia, silver azide, potassium, sodium, oxygen difluoride. Incompatible with aluminum-titanium alloy, barium acetylide, ethanol, formamide, halogens, mercmic oxide, mercurous chloride, oxygen, pyridine, pyrogallic acid, salicylic acid sodium hydride, sodium salicylate, sulfides, and other materials. 

Electrophilic mercuration of isoxazoles parallels that of pyridine and other azole derivatives. The reaction of 3,5-disubstituted isoxazoles with raercury(II) acetate results in a very high yield of 4-acetoxymercury derivatives which can be converted into 4-broraoisoxazoles. Thus, the reaction of 5-phenylisoxazole (64) with mercury(II) acetate gave mercuriacetate (88) (in 90% yield), which after treatment with potassium bromide and bromine gave 4-bromo-5-phenylisoxazole (89) in 65% yield. The unsubstituted isoxazole, however, is oxidized under the same reaction conditions, giving mercury(I) salts. 

In the case of mercuration (soft electrophile), attack at the 2-position is favoured. These observations accord with predictions based on molecular orbital calculations, that hard electrophiles (nitronium ions) should attack at C-4 and soft electrophiles (e.g. HgS04) at C-2 (68JA223). Furthermore, very hard electrophiles (e.g. S03) are predicted to attack at C-3. This is hard to verify because pyridine 1-oxide reacts at C-3 as its conjugate acid (or... 

Isoquinoline forms a 4-acetoxymercuri derivative. Pyridine 1-oxide is mercurated predominantly in the 2-position, but increasing acidity increases the proportion of 3-mercuri product formed. 

Key A, ethanol B, methanol C, chloroform D, water E, pyridine F, methanol-water (9 1) Key SC, silver carbonate SO, silver oxide MC, mercuric cyanide.e Key AZ, azeotropic distillation M, magnesium sulfate CS, calcium sulfate Key PD, p-dioxane, BZ, benzene CT, carbon tetrachloride DCM, dichloromethane DCE, 1,2-dichloroethane TCE, 1,1,2-trichlorocthanc. 

Lithium aluminium hydride reduction of lucidusculine (35) afforded napelline (34) in quantitative yield. Napelline was hydrogenated with platinum oxide in acetic acid to afford dihydronapelline (286). Treatment of 286 with mercuric acetate in aqueous acetic acid followed by oxidation with chromium trioxide in pyridine afforded 287 in 16.5% yield. Ketalization of 287 yielded 285 in a yield of 71%. On refluxing 285 with methanolic base, a 4 6 equilibrium mixture of 285 and 288 was obtained. These compounds... 

Sulfonation of pyridine A-oxide requires the use of 20% fuming sulfuric acid and a mercuric sulfate catalyst with prolonged heating at 230°. Under these conditions, the main product is the 3-sulfonic acid (40-45%) together with small amounts of the 2- (0.5-1%) and 4-sulfonic acids (2-2.5%).214 2,6-Lutidine V-oxide reacts under similar conditions, substitution taking place at C-3.215... 

Formyl-l,2,3,3-tetramethylindoline (29) was converted to various 5-([3-heterocyclylvinyl) indolines (30) via condensation with heterocyclic quaternary salts and subsequent N-dealkylation by triphenylphosphine. The resultant indolines were oxidized with mercuric acetate to the 5-substituted Fischer s bases (31, R = benzoxazol-2-yl quinolin-2-yl quinolin-4-yl pyridin-4-yl 1,3,3-trimethylindo-len-2-yl). These were used as intermediates for cyanine dyes their conversion to spiropyrans was not recorded. 41... 

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