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Chemicals >> Reducing Agents

Sodium cyanoborohydride, Sodium cyanotrihydroborate

Sodium cyanoborohydride is especially suitable for reductive aminations. Since the reaction rate for the reduction of iminium ions is much faster than for ketones or even aldehydes, the reductive amination can be carried out as a one-pot procedure by introducing the reducing agent into a mixture of the amine and carbonyl compound.

Contact with strong acids liberates the highly toxic gas HCN. A safer reducing agent with comparable reactivity is sodium triacetoxyborohydride.

Recent Literature

Tin-free Giese reaction of alkyl iodides with electron-deficient alkenes and the related radical carbonylation process proceeded efficiently in the presence of sodium cyanoborohydride and tetrabutylammonium cyanoborohydride. Transfer of iodine followed by hydride reduction of the resulting carbon-iodine bond is proposed as a possible mechanism.
I. Ryu, S. Uehara, H. Hirao, T. Fukuyama, Org. Lett., 2008, 10, 1005-1008.

By optimizing the metal hydride/ammonia mediated reductive amination of aldehydes and hemiacetals, primary amines were selectively prepared with no or minimal formation of the usual secondary and tertiary amine byproduct. The methodology was performed on a range of functionalized aldehyde substrates, including in situ formed aldehydes from a Vasella reaction.
E. M. Dangerfield, C. H. Plunkett, A. L. Win-Mason, B. L. Stocker, M. S. M. Timmer, J. Org. Chem., 2010, 75, 5470-5477.

An aryloxotitanium complex is a highly chemo- and regioselective catalyst for intermolecular hydroamination of terminal alkynes. Branched imines are obtained in good yield with various primary aromatic and aliphatic amines.
V. Khedkar, A. Tillak, M. Beller, Org. Lett., 2003, 5, 4767-4770.

Manganese dioxide is employed as an in situ oxidant for the one-pot conversion of alcohols into imines. In combination with polymer-supported cyanoborohydride (PSCBH), a one-pot oxidation-imine formation-reduction sequence enables alcohols to be converted directly into both secondary and tertiary amines.
L. Blackburn, R. J. K. Taylor, Org. Lett., 2001, 3, 1637-1639.

A preparation of highly substituted β-amino acids involves a Vilsmeier-Haack reaction with nonaromatic carbon nucleophiles. The reaction enabled the synthesis of several β2,2,3-amino esters, such as derivatives of homoproline, homoalanine, and homopipecolinic esters.
A. Roamens, G. Bélanger, Org. Lett., 2015, 17, 322-325.

The selective aldimine cross-coupling represents a simple and flexible method for the synthesis of highly substituted unsymmetrical 1,2-diamines. In addition, either the syn- or anti-configurated vicinal diamine can be obtained, depending on the choice of the workup and reduction conditions.
C. Kison, N. Meyer, T. Opatz, Angew. Chem. Int. Ed., 2005, 44, 5662-5664.

A Lewis acid-catalyzed three-component, mild, highly atom econocial, direct-type Mannich reaction of simple aromatic and enolizable aliphatic aldehydes, secondary amines, and glycine derivatives affords various synthetically important anti-α,β-diamino ester derivatives in high yields with high diastereoselectivities.
M. M. Salter, J. Kobayashi, Y. Shimizu, S. Kobayashi, Org. Lett., 2006, 8, 3533-3536.