Grignard reagents nucleophilic substitution

The reaction involves nucleophilic substitution of for OR and addition of R MgX to the carbonyl group. With 1,4-dimagnesium compounds, esters are converted to cyclopentanols (40). Lactones react with Grignard reagents and give diols as products. 

In some instances a carbon-carbon bond can be formed with C-nucleophiles. For example, 3-carboxamido-6-methylpyridazine is produced from 3-iodo-6-methylpyridazine by treatment with potassium cyanide in aqueous ethanol and l,3-dimethyl-6-oxo-l,6-dihydro-pyridazine-4-carboxylic acid from 4-chloro-l,3-dimethylpyridazin-6-(lH)-one by reaction with a mixture of cuprous chloride and potassium cyanide. Chloro-substituted pyridazines react with Grignard reagents. For example, 3,4,6-trichloropyridazine reacts with f-butyl-magnesium chloride to give 4-t-butyl-3,5,6-trichloro-l,4-dihydropyridazine (120) and 4,5-di-t-butyl-3,6-dichloro-l,4-dihydropyridazine (121) and both are converted into 4-t-butyl-3,6-dichloropyridazine (122 Scheme 38). 

Heterocyclic structures analogous to the intermediate complex result from azinium derivatives and amines, hydroxide or alkoxides, or Grignard reagents from quinazoline and orgahometallics, cyanide, bisulfite, etc. from various heterocycles with amide ion, metal hydrides,or lithium alkyls from A-acylazinium compounds and cyanide ion (Reissert compounds) many other examples are known. Factors favorable to nucleophilic addition rather than substitution reactions have been discussed by Albert, who has studied examples of easy covalent hydration of heterocycles. 

Grignard reagents do react with epoxides 24 by an SN2-mechanism, resulting in a ring-opening reaction. An epoxide carbon bearing no additional substituent—i.e. a methylene group—is more reactive towards nucleophilic attack than a substituted one ... 

Methods of synthesis for carboxylic acids include (1) oxidation of alkyl-benzenes, (2) oxidative cleavage of alkenes, (3) oxidation of primary alcohols or aldehydes, (4) hydrolysis of nitriles, and (5) reaction of Grignard reagents with CO2 (carboxylation). General reactions of carboxylic acids include (1) loss of the acidic proton, (2) nucleophilic acyl substitution at the carbonyl group, (3) substitution on the a carbon, and (4) reduction. 

Acid halides are among the most reactive of carboxylic acid derivatives and can be converted into many other kinds of compounds by nucleophilic acyl substitution mechanisms. The halogen can be replaced by -OH to yield an acid, by —OCOR to yield an anhydride, by -OR to yield an ester, or by -NH2 to yield an amide. In addition, the reduction of an acid halide yields a primary alcohol, and reaction with a Grignard reagent yields a tertiary alcohol. Although the reactions we ll be discussing in this section are illustrated only for acid chlorides, similar processes take place with other acid halides. 

Conversion of Esters into Alcohols Grignard Reaction Esters and lactones react with 2 equivalents of a Grignard reagent to yield a tertiary alcohol in which two of the substituents are identical (Section 17.5). The reaction occurs by the usual nucleophilic substitution mechanism to give an intermediate ketone, which reacts further with the Grignard reagent to yield a tertiary alcohol. 

Generally, in contrast to 2-substituted cyclopentanones, the diastereoselectivity of addition reactions to 3-substituted cyclopentanones is nearly independent of the nucleophile and the substituent in the 3-position. Thus, addition of various Grignard reagents, including ethynyl reagents, to 3-methyl- and 3-ferf-butylcyclopentanone leads to almost the same ratio of diastereomers (Table 3)3,4 6, 27,2s... 

Reactions of highly electron-rich organometalate salts (organocuprates, orga-noborates, Grignard reagents, etc.) and metal hydrides (trialkyltin hydride, triethylsilane, borohydrides, etc.) with cyano-substituted olefins, enones, ketones, carbocations, pyridinium cations, etc. are conventionally formulated as nucleophilic addition reactions. We illustrate the utility of donor/acceptor association and electron-transfer below. 

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