Esters functional group interconversion

Furazan- and furoxan-carboxylic acids are thermally and hydrolytically unstable decomposing to a-(hydroxyimino)nitriles, but their amide, ester, halide, and nitrile derivatives are readily accessible and all undergo the expected functional group interconversions. Dicyanofuroxan reacts with hydroxylamine to give the fused oxazino compound (63) and the pyridazino analogue (64) is similarly formed with hydrazine <82H(19)1063>. 

A stereoselective synthesis of 2,3,5,6-tetra- and 2,3,4,5,6-penta-substituted piperidines was achieved from oxidative cleavage of 2-azabicyclo[2.2.2]octane Diels-Alder adducts 176 derived from dihydropyridine 177. Appropriate functional group interconversions of the amidine and ester functionalities in 176 ultimately gave densely functionalized piperidines such as 178 <05OL5773> (Scheme 51). 

Converting one functional group into another is called functional group interconversion. Our knowledge of oxidation-reduction reactions has greatly expanded our ability to carry out functional group interconversions. For example, an aldehyde can be converted into a primary alcohol, an alkene, a secondary alcohol, a ketone, a carboxylic acid, an acyl chloride, an ester, an amide, or an amine. 

Sn2 reactions are highly useful in organic synthesis because they enable us to convert one functional group into another—a process that is called a funcdonal group trausfonna-tion or a functional group interconversion. With the Sn2 reactions shown in Fig. 6.11, methyl, primary, or secondary alkyl halides can be transformed into alcohols, ethers, thiols, thioethers, nitriles, esters, and so on. Note. The use of the prefix thio- in a name means that a sulfur atom has replaced an oxygen atom in the compound.)... 

The enantioselective hydrocyanation of alkenes has the potential to serve as an efficient method to generate optically active nitriles, as well as amides, esters, and amines after functional group interconversions of the nitrile group. As in asymmetric hydroformylation, asymmetric hydrocyanation requires control of both regiochemistry and stereochemistry because simple olefins tend to generate achiral terminal nitrile products. The hydrocyanation of norbomene will give a single constitutional isomer and was studied initially. However, modest enantioselectivities were obtained, and the synthetic value is limited. ... 

Resolution of compounds containing functional groups that are not acidic or basic requires a reversible functional group interconversion involving a chiral resolving agent. For example, the reaction of a racemic alcohol with a chiral carboxylic acid results in a mixture of diastereomeric esters that can be separated. After separation, hydrolysis of the ester regenerates the desired alcohol. To resolve a racemic ketone or aldehyde, a reaction with a chiral diol or a chiral amine could be employed to form diastereomeric acetals or imines, respectively. 

An interesting reductive functional group interconversion employed the Brook rearrangement of the disilyl carbinol formed upon addition of two equivalents of a silyllithium to an ester. For example, 94 imderwent Brook rearrangement to silyl ether 95, and silicon-carbon bond oxidation provided the aldehyde in good overall yield. ... 

WeVe talked at length about the interconversions of acid derivatives, explaining the mechanism of attack of nucleophiles such as ROH, H20, and NH3 on acyl chlorides, acid anhydrides, esters, acids, and amines, with or without acid or base present. We shall now go on to talk about substitution reactions of acid derivatives that take us out of this closed company of compounds and allow us to make compounds containing functional groups at other oxidation levels such as ketones and alcohols. 

Temperature-jump experiments were performed with aqueous solutions of 2-chloro-4(l/7)-pyridone and 2,6-di(methoxycarbonyl)-4(17/)-pyridone (chelidamic acid dimethyl ester). It was suggested that when the tautomeric functional group is remote, tautomeric interconversion occurs through intermediate ionization and dissociation followed by ion recombination (77JA4438). 

Alcohols are particularly important in both laboratory and biochemical transformations of organic compounds. They can be converted into other types of compounds, such as al-kenes, haloalkanes, aldehydes, ketones, carboxylic acids, and esters. Not only can alcohols be converted to these compounds, but they also can be prepared from them.Thus, alcohols play a central role in the interconversion of organic functional groups. 

In the second group we consider interconversions of functional groups with the exchange of hetereoatoms, breaking of old and formation of new C-heteroatom bonds. Examples of these transformations are interconversion of an amide to ester, thioketone to ketone or alkylhalide to alcohol. They are related to S5mthetic reactions formation of amide from ester, thioketone from ketone or haloalkane from alcohol. Characteristic of all the above interconversions is the disconnection (imaginative process ) of the C-heteroatom bond, C-N or C-O. In the synthetic direction C-N, C-S and C-Hal bonds are formed. Therefore, such FGIs are also denoted as DIS-C-X, where X stands for heteroatom. 

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