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.
