Easily reducible functional groups

Catalytic hydrogenation transfers the elements of molecular hydrogen through a series of complexes and intermediates. Diimide, HN=NH, an unstable hydrogen donor that can be generated in situ, finds specialized application in the reduction of carbon-carbon double bonds. Simple alkenes are reduced efficiently by diimide, but other easily reduced functional groups, such as nitro and cyano are unaffected. The mechanism of the reaction is pictured as a concerted transfer of hydrogen via a nonpolar cyclic TS. 

Reductive cleavages of C— C bonds can also take place when one and even the two carbonyl groups are replaced by other easily reduced functional groups. The only requirement appears to be the proper syn- or anti peri planar orientation of the reacting functional groups with the C —C bond to be cleaved. The following transformations 279 + 280 and 281 + 282 reported by Baker and Davis (81) and Paquette and Wyvratt (82) respectively constitute representative cases. 

Probably, L-selectride might have been replaced by milder reagents, for instance nucleophiles like PPh3, thiourea, etc.31), therefore extending the range of diverse structures containing easily reducible functional groups. 

Finally, the value of a specific reducing system reflects its ability to reduce the enone function chemoselectively in the presence of other easily reducible functional groups. 

Polynitroaromatic compounds are reduced more easily than mono-nitro compounds. Additional nitro groups facilitate the reduction however, the reduced functional groups, hydroxylamine and amine, hinder the reduction of other nitro groups. At pH < 3 the reduction of dinitroaromatic compounds follows two four-electron steps ... 

A procedure for the cathodic reduction of anthranilic acid to the corresponding alcohol is described in Organic Synthesis [36]. Because the carboxylic acid group is so difficult to reduce, the method cannot normally be used for acid substituted with easily reducible functions or groups. For instance, pentafluorobenzoic acid loses fluorine by cathodic cleavage at mercury, in 20% sulfuric acid, at —1.20 V (SCE) 2,3,5,6-tetrafluor-obenzoic acid is obtained in 75% yield [38]. However, at potentials more negative than... 

Hydroboration is readily effected with alkenes containing many types of functional group. Where the other functional group is not reduced by borane, hydroboration generally proceeds without difficulty and even some functional groups that react only slowly with borane may be tolerated, for example carboxylic esters. Easily reduced carbonyl groups of aldehydes and ketones, however, must be protected as their acetals, and carboxylic acids as esters. 

Polarography is used extensively for the analysis of metal ions and inorganic anions, such as lOg and NOg. Organic compounds containing easily reducible or oxidizable functional groups also can be studied polarographically. Functional groups that have been used include carbonyls, carboxylic acids, and carbon-carbon double bonds. 

A frequently occurring problem is the full or partial reduction of a nilro function in the presence of other reducible functions. Preferential hydrogenation of an aromatic nilro group can usually be achieved for it is very easily reduced. 

Derivatives of hydrazine, especially the hydrazide compounds formed from carboxylate groups, can react specifically with aldehyde or ketone functional groups in target molecules. Reaction with either group creates a hydrazone linkage (Reaction 44)—a type of Schiff base. This bond is relatively stable if it is formed with a ketone, but somewhat labile if the reaction is with an aldehyde group. However, the reaction rate of hydrazine derivatives with aldehydes typically is faster than the rate with ketones. Hydrazone formation with aldehydes, however, results in much more stable bonds than the easily reversible Schiff base interaction of an amine with an aldehyde. To further stabilize the bond between a hydrazide and an aldehyde, the hydrazone may be reacted with sodium cyanoborohydride to reduce the double bond and form a secure covalent linkage. 

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