Reductive amination, of aldehydes and

Sodium cyanoborohydride is remarkably chemoselective. Reduction of aldehydes and ketones are, unlike those with NaBH pH-dependent, and practical reduction rates are achieved at pH 3 to 4. At pH 5—7, imines (>C=N—) are reduced more rapidly than carbonyls. This reactivity permits reductive amination of aldehydes and ketones under very mild conditions (42). 

Besides direct reduction, a one-pot reductive amination of aldehydes and ketones with a-picoline-borane in methanol, in water, and in neat conditions gives the corresponding amine products (Scheme 8.2).40 The synthesis of primary amines can be performed via the reductive amination of the corresponding carbonyl compounds with aqueous ammonia with soluble Rh-catalyst (Eq. 8.17).41 Up to an 86% yield and a 97% selectivity for benzylamines were obtained for the reaction of various benzaldehydes. The use of a bimetallic catalyst based on Rh/Ir is preferable for aliphatic aldehydes. 

Table 14. organosilane reductive amination of aldehydes and ketones... 

Table 14. Organosilane Reductive amination of aldehydes and Ketones (Continued)...

Supplemental References for Table 14. Organosilane Reductive Amination of Aldehydes and Ketones... 

Although imine hydrogenation is discussed in greater detail in Chapter 34, it seems appropriate at this point to describe one-pot reductive amination of aldehydes and ketones. The reductive amination of aldehydes and ketones using so-... 

Quaternary ammonium cyanoborohydrides have been used for the reduction of iminium salts [14] and in the reductive amination of aldehydes and ketones [15]. 

Abdel-Magid, A. F. Carson, K. G. Harris, B. D. Maryanoff, C. A. Shah, R. D. Reductive Amination of Aldehydes and Ketones with Sodium Triace-toxyborohydride. Studies on Direct and Indirect Reductive Amination Procedures, J. Org. Chem. 1996, 67, 3849. 

A review describing the major advances in the field of asymmetric reduction of achiral ketones using borohydrides, exemplified by oxazaborolidines and /9-chlorodiisopino- camphenylborane, has appeared. Use of sodium borohydride in combination with chiral Lewis acids has been discussed.298 The usefulness of sodium triacetoxyboro-hydride in the reductive amination of aldehydes and ketones has been reviewed. The wide scope of the reagent, its diverse and numerous applications, and high tolerance for many functional groups have been discussed.299 The preparation, properties, and synthetic application of lithium aminoborohydrides (LABs) have been reviewed. 

The alkylation of ammonia, Gabriel synthesis, reduction of nitriles, reduction of amides, reduction of nitrocompounds, and reductive amination of aldehydes and ketones are methods commonly used for preparing amines. 

Reductive amination of aldehydes and ketones can also be accomplished in that way provided the pH is 6-8. 

The reduction of enamine unit occurs much more rapidly than that of the carbonyl group. Therefore, this reagent can be used to perform reductive amination of aldehydes and ketones, by simply reacting the carbonyl compound with a fourfold excess of the amine. In a similar manner, reductive methylation of amines could be accomplished by addition of formaldehyde to the amine119. 

Yields for such reductions are in the range S0-8S %. This ready reduction of iminium salts makes possible reductive amination of aldehydes and ketones at pH 6 ... 

Probably the most useful application of the reagent is for reductive amination of aldehydes and ketones. The carbonyl compound is allowed to react with ammonia or primary or secondary amines at pH <7 in absolute methanol in the... 

An important additional amine synthesis in this section is reductive amination of aldehydes and ketones. In particular, reductive amination of a ketone is a better way to make an amine attached to a 2° alkyl group than is Sn2 reaction with a 2° haloalkane. 

Iminium groups are more easily reduced than carbonyl groups in acid solution, and this has been exploited in a method for reductive amination of aldehydes and ketones by way of the iminium salts formed from the carbonyl compounds and... 

Catal)rtic reactions often give surprising results. An interesting result is the reductive amination of aldehydes and ketones. The keto compounds react with primary or secondary amines or ammonia in the presence of H2 and a suitable catalyst (e.g., Pd) to give a new amine. Thus, as expected, 2-methylcyclohexanone is converted to 2-methylcyclohexylamine (Eq. 8-16). 

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