Carboxylic esters halogenation

The Reforrnatsku reaction of a-halogenated carboxylic esters with silylated cyanohydrins combined with an intramolecular acylation reaction gives fluorinated derivatives of tetronic acid [28] (equation 17) It is noteworthy to mention that this particular reaction sequence only proceeds with ultrasonic irradiation A very... 

With acyl halides, the corresponding acyl phosphonates are obtained. Furthermore allylic and acetylenic halides, as well as a-halogenated carboxylic esters and dihalides, can be used as starting materials. If substituents R and R are different, a mixture of products may be obtained, because the reaction product RX 5 can further react with phosphite 1 that is still present ... 

Darzens reactions between the chiral imine 52 and a-halo enolates 53 for the preparation of nonracemic aziridine-2-carboxylic esters 54 (Scheme 3.17) were studied by Fujisawa and co-workers [61], It is interesting to note that the lithium enolate afforded (2K,3S)-aziridirie (2i ,3S)-54 as the sole product, whereas the zinc enolate give rise to the isomer (2S,3i )-54. The a-halogen did not seem to affect the stereoselectivity. 

The alkylation of activated halogen compounds is one of several reactions of trialkylboranes developed by Brown (see also 15-16,15-25,18-31-18-40, etc.). These compounds are extremely versatile and can be used for the preparation of many types of compounds. In this reaction, for example, an alkene (through the BR3 prepared from it) can be coupled to a ketone, a nitrile, a carboxylic ester, or a sulfonyl derivative. Note that this is still another indirect way to alkylate a ketone (see 10-105) or a carboxylic acid (see 10-106), and provides an additional alternative to the malonic ester and acetoacetic ester syntheses (10-104). 

A number of other methods exist for the a halogenation of carboxylic acids or their derivatives. Acyl halides can be a brominated or chlorinated by use of NBS or NCS and HBr or HCl. The latter is an ionic, not a free-radical halogenation (see 14-2). Direct iodination of carboxylic acids has been achieved with I2—Cu acetate in HOAc. " ° Acyl chlorides can be a iodinated with I2 and a trace of HI. Carboxylic esters can be a halogenated by conversion to their enolate ions with lithium A-isopropylcyclohexylamide in THF and treatment of this solution at -78°C with... 

Solvents can be classified into three categories according to their polarity namely, polar protic, dipolar aprotic and non-polar. Most of the common solvents fall under one of following chemical classes Aliphatic hydrocarbons, aromatic hydrocarbons, alcohols, phenols, ethers, aldehydes, ketones, carboxylic acids, esters, halogen-substituted hydrocarbons, amines, nitriles, nitro-derivatives, amides and sulfur-containing solvents (Marcus, 1998). In certain cases a mixture of two or more solvents would perform better than a single solvent. 

The presence of bis[2-(A,A-dimethylamino)ethyl]ether allows a selective halogen-magnesium exchange of iodo- and bromoaromatics at ambient temperature using iso-propylmagnesium chloride. Sensitive carboxylic ester and cyano groups are well tolerated (equations 29 and 30). ... 

Alkylation of Ketones, Nitriles, and Carboxylic Esters a-Acylalkyl-de-halogenation, etc. 

Tables II to X give the melting points and, where applicable, the optical rotations of the inositols, inososes, inosamines, and quercitols, and of all of their known O-substituted derivatives. Anhydroinositols, although not substitution products in the strict sense, are included, as are the carbonyl-functional derivatives of the inososes. Halogen- and nitro-substituted cyclitols, and the C-methyl-inositols and their derivatives, are not included most of these compounds are referred to in the text. The derivatives are arranged in the following order salts (inosamines) or functional derivatives (inososes), carboxylic esters, borates, nitrates, sulfonic esters, phosphates, glycosides, acetals (and Schiff bases), ethers (and IV-alkyl derivatives), and anhydrides.

Z = electron-withdrawing substituent, e.g. halogen, carboxylic ester or perhaloalkyl... 

Halogenated dicarboxylic acids, (I) and (n), prepared by the author (2,3), respectively, and carboxylic ester diacids (HI) prepared by Alonso-Alija (4) were also effective in stimulating cGMP formation and used in the treatment of cardiovascular diseases. 

I he method is. superior to the usual procedure of refluxing the carboxylic ester with halogen and phosphorus trichloride. ... 

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