Phosphorus pentachloride reaction with ketones

After having determined the nature of the side reaction it became clear that in order to obtain the desired ethynylpyrazole 11 the reaction between the ketone and PCI5 would have to be performed at low temperature. Indeed, the reaction was carried out in CH2CI2 at room temperature and a mixture of chlorides 7 and 8 was obtained. Dehydrochlorination of this mixture gave 66% of 3,5-dimethyl-4-ethynylpyrazole (11). Thus, by varying the conditions it is possible to carry out the reaction of the ketone with phosphorus pentachloride selectively in any of the above-mentioned directions. 

Ketones can be converted to gem-dichloride through their reaction with phosphorus pentachloride which can be used to synthesize alkynes. 

Cyclic 1,3-diketones have been converted into / -halogeno-ketones (118) by tri-phenylphosphine dihalides in benzene or acetonitrile,100 although this paper adds little to previous work101 in this field. The reactions of phosphorus pentachloride with acetals have been extended to mixed acetals, such as (119).102 Only one product... 

Acylation of the keto acid (637) leads to the isobenzopyrylium salt (638) (77CHE1183). However, the isobenzopyrylium salt (639), a potential intermediate for the synthesis of analogues of berberine alkaloids, results from the formylation of the substituted ketone or the isochromanone (640) using dichloromethyl butyl ether (Scheme 251) (81CHE221). A second product, the 5-oxoniachrysene (641), is formed and this compound may also be obtained by reaction of the isobenzopyrylium salt with phosphorus pentachloride and then with triethylamine. The intermediacy of a cyclic vinyl ether is proposed. 

Exercise 30-6 Reduction of the ketone group of (—)-menthone, which has its alkyl groups trans to one another, gives two products, known as (—(-menthol and (+)-neomenthol. These two substances differ considerably in their reactions. (+)-Neomenthol undergoes dehydration either in methanoic acid or when treated with phosphorus pentachloride, whereas (—(-menthol gives a methanoate ester with methanoic acid and a chloride with phosphorus pentachloride. What is the relationship between neomenthol and menthol, and why do they behave differently with methanoic acid and phosphorus pentachloride What is the likely structure of the menthene from dehydration of neomenthol (Review Sections 8-8D, 12-3D, and 12-5.)... 

A simple method for introducing a triple bond into an organic compound is to treat an appropriate dihalide with a strong base. Since vicinal dihalides (usually the bromide) are readily formed by reaction of bromine with an alkene, and geminal dihalides from aldehydes or ketones with phosphorus pentachloride, the method is a useful general procedure for the preparation of terminal and non-terminal alkynes from readily available starting materials. 

The reaction of phosphorus pentachloride with aliphatic aldehydes or ketones has been used to prepare gew-dihalides. These compounds are important intermediates in the synthesis of acetylenes (method 43). 

Often, a large quantity of hydrogen chloride is evolved with the formation of monochloroSlefins, RC(Cl) = CHR however, the resulting mixture is suitable for the acetylene synthesis. Small amounts of dichloro compounds of the type RCHCICHCIR are also formed. These side reactions ate limited by adding the ketone to the phosphorus pentachloride at 0° C... 

Treatment of cyclopropyl ketones with phosphorus pentachloride afforded (1,1-dichloroal-kyl)cyclopropane derivatives in variable yield. ss-iass jjjg reaction can be hampered by ring opening if the reaction is performed above room temperature. Thus, treatment of phenyl 1 -phenylcyclopropyl ketone with phosphorus pentachloride in carbon tetrachloride gave l-[dichloro(phenyl)methyl]-l-phenylcyclopropaneas the sole product at ambient temperature, whereas a second product, l,4-dichloro-l,2-diphenylbut-l-ene, was formed in addition at reflux temperature. ... 

The reaction of sulfur tetrafluoride with ketones is very similar to that of phosphorus pentachloride. Sulfur tetrafluoride will lose a fluoride ion to form the more... 

Tetrachloropyrimidine is formed in quantitative yield by the cyclization (with FeCla, at 200 °C) of perchloro-l-cyano-3-azabutadiene (Cl2C=N—CC1=CC1CN), itself formed by successive treatment of cyanoethyl)formamide with phosphorus pentachloride and chlorine. j8-Iminoyl-enamines (222), prepared by the reaction of the appropriate anils with nitriles, condense with ethyl chloroformate and carbon disulphide to give excellent yields of 2-oxo- and 2-thioxo-pyrimidines (223 X = O or S). Aldehydes, acetals, and ketals (but not ketones) also react with these enamines (222) to give 1,2-dihydropyrimidines (224) (70—93%). In similar fashion, malondiamidines condense with a large variety of aromatic aldehydes to give 2-aryl-5-arylmethyl-4,6-diaminopyrimidines. °... 

When W-acetyltetrahydrojervine (LXIV) is reacted with phosphorus pentachloride a desoxychloro derivative (LXXXIV) is formed which on ring scission with sulfuric acid in acetic anhydride-acetic acid gives rise to the 0,iV-diacetyl compound LXXXV. This on partial hydrolysis with alkali affords an W-acetyl compound (LXXXVI) which on reacetylation yields an isomeric diacetyl derivative (LXXXVII) in analogy with similar reactions of tetrahydrojervine. The AT-acetyl derivative (LXXXVI) on chromic acid oxidation formed a ketone (LXXXVIII) with a reactive carbonyl (66). 

A geminal dihalide (abbreviated gem-diAiaAiAf has two halogen atoms bonded to the same carbon geminus, Latin twins). Ketones can be converted to m-dichlorides by reaction with phosphorus pentachloride, and the jf wj-dichlorides can be used to synthesize alkynes. 

Fresenius, passing his pharmacy examination in 1877. He then joined Kolbe, and his assistant, Ernst von Meyer, and started work on the oxidation of dialkyl sulfides. For this research Beckmann received his PhD in July 1878. Beckmann tried to apply an already-known reaction to discriminate between aldehydes and ketones. This reaction involved the use of hydroxylamine to convert benzophenone into an oxime. Treating this oxime with phosphorus pentachloride he converted it into a substance already characterized by Wallach. This reaction is now known as the Beckmann rearrangement. 

Alkynes can be prepared by elimination reactions under conditions similar to those used to form alkenes. Because an alkyne has two n bonds, two molar equivalents of HX must be eliminated from the starting material. One such suitable reactant is a vicinal dihahde, a compound with halogen atoms on adjacent carbon atoms. We recall that such compounds result from the addition of a halogen to the double bond of an alkene (Section 6.5). A geminal dihahde, which has both halogens on the same carbon atom, can also be used to synthesize alkynes. Geminal dichlorides can be made by reaction of phosphorus pentachloride with an aldehyde or ketone. 

The oxygen of ketone and aldehyde groups is readily replaced by halogen under the influence of phosphorus trichloride or pentachloride the reaction may be carried out with or without a solvent solvents commonly employed are chloroform, benzene, petroleum ether, acetyl chloride and phosphorus oxychloride. 

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