Pyridine, reactions with—continued methanol

In the course of the continuing study [9a,b] on the enantioselective addition of dialkylzincs to aldehydes by using chiral amino alcohols such as diphenyl(l-methyl-2-pyrrolidinyl)methanol (45) (DPMPM) [48] A. A -dibutylnorephedrine 46 (DBNE) [49], and 2-pyrrolidinyl-l-phenyl-1-propanol (47) [50] as chiral catalysts, Soai et al. reacted pyridine-3-carbaldehyde (48) with dialkylzincs using (lS,2/ )-DBNE 46, which gave the corresponding chiral pyridyl alkanols 49 with 74-86% ee (Scheme 9.24) [51]. The reaction with aldehyde 48 proceeded more rapidly (1 h) than that with benzaldehyde (16 h), which indicates that the product (zinc alkoxide of pyridyl alkanol) also catalyzes the reaction to produce itself. This observation led them to search for an asymmetric autocatalysis by using chiral pyridyl alkanol. 

Fohlisch reported in 1971 the use of enaminones derived from the reaction of dimethyIformamide acetal with the methyl group of acetophenones in a convenient synthesis of chromanones (12). It was found that upon refluxing o-hydroxyacetophenone in the presence of dimethylformamide acetal and xylene, with continuous removal of the methanol formed in the reaction, an 80% yield of the intermediate enaminone 12 was obtained. Treatment of 12 with dilute acid then gave the desired chromanone 13 in 71% yield. Thus, to utilize this reaction in our synthesis of dihydropyrano[2,3-b]pyridines, the acetyl-pyridone 15 was chosen as our starting compound. 

Polyiphenylene sulfide). A 200 mL, three-neck, round-bottom flask equipped with a magnetic stirring bar, reflux condenser, thermometer, and N2 gas in inlet charged with PPST (1 g, 2.6 nunol) and pyridine (10 mL). The reaction mixture was stirred at room temperature and after a few minutes, the reaction mixture turned into a white suspension. The reaction was continued for 1 h at room temperature and then the temperature was slowly raised to reflux. The reaction was continued for 20 h at reflux temperature. The reaction was quenched by cooling it to room temperature and pouring into methanol (2(X) mL, 10% HCI). The precipitate was washed with methanol and chloroform. The polymer was purified by continuous extraction in a Sorhlet apparatus with methanol for 5 h and was dried in vacuo at 60 <>C for 20 h. The resulting polymer was isolated as a white powder. Yield 0.56g, 99%. IR(KBr,cm-i) ... 

Jacobsen (1999) has carried out carbomethoxylation of asymmetric epoxides. Thus, the carbomethoxylation of (R)-propylene oxide with CO and methanol yields 92% of (3R)-hydroxybutanoic acid in greater than 99% ee. Similarly, the reaction of (/ )-epichlorohydrin gives 96% of 4-chloro-(3R)-hydroxybutanoic acid in greater than 99% ee. The catalyst consists of dicobalt octacarbonyl and 3-hydroxy pyridine. A continuous process for making enantiomeric 1-chloro-2-propanol has been suggested. With a suitable catalyst propylene reacts with O2, water, cupric and lithium chloride to give 78% of (S)-l-chloro-2-propanol in 94% ee. 

A mixture of 30.6 parts of cis-2-(2,4-dichlorophenyl)-2-(lH-l,2,4-triazol-l-ylmethyl)-l,3-dioxolane-4-methanol and 75 parts of pyridine is stirred at room temperature and there are added dropwise 17.2 parts of methanesulfonyl chloride. Upon completion, stirring is continued overnight at room temperature. The reaction mixture is poured onto ice-water and the product is extracted twice with dichloromethane. The combined extracts are washed... 

Phenyl terminated polybutadiene (M 1300 daltons, 45% vinyl) was reacted with trichlorosilane and chloroplatinic acid and then mixed with a slurry of 105 p particle size silica gel having a 250 A average pore diameter in dry toluene for 24 hours. The quantity of trichlorosilane used was 2 mol per mole of polybutadiene. Pyridine was added to remove HCl, and the slurry was gently shaken for 18 hours at ambient temperature. The surface of the silica was blocked by addition of 1,2-bis(trichlor-osilyl)ethane, and the mixture was treated with pyridine. After three hours of shaking the reaction was worked up by vacuum filtration in a sintered glass funnel and washed with toluene and methanol. The modified silica gel was dried in the filter funnel by continued application of vacuum to the filter funnel. 

To a stirred pyridine solution (30 mL) of benzenetetracarbonyl tetrachloride (5.5 g, 17 mmol), prepared from benzenetetracarboxylic anhydride and phosphorous penta-chloride, was added portionwise (-)-bomeol (10.3 g, 67 mmol) at 0 °C, and stirring was continued for 18 h under a nitrogen atmosphere. The reaction mixture was then poured into a mixture of 6% aqueous hydrogen chloride (150 mL) at 5 °C (ice bath) and extracted with three portions of ether (200 mL). The combined organic extracts were washed with saturated aqueous sodium bicarbonate and brine, dried over magnesium sulfate, and then evaporated to dryness under a reduced pressure. The crude product obtained was purified by repeated recrystallization from methanol and then twice from hexane to yield pure (-)-tetrabornyl 1,2,4,5-benzenetetracarboxylate (8.0 g, 60%), mp 239.5 - 241.0 °C, [a]p = -59.5° (0.9, benzene). 

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