as an important catalyst for various transformations. The
moistened reagent is nonpyrophoric in nature relative to
many metal hydrogenation catalysts. It was reported to be an
efficient catalyst for reduction of azides to amines16 as well as
reduction of aromatic nitro compounds to anilines.18 It is also
reported to perform reduction of carboxylic acid anhydrides,19
hydrochlorination of chloroaromatics,20 reduction of allylic
hydroperoxides to hydroxides,21 deoximercuration of organic
mercurials,22 reductive removal of allylic functional groups,23
etc.
In the present method nickel boride generated in situ from
nickel chloride hexahydrate and sodium borohydride was used
for reductive amination of aldehydes and ketones. Four differ-
ent aldehydes and four different ketones were reductively
aminated with n-butylamine, benzylamine and aniline respect-
ively to give the corresponding secondary amines within a few
minutes. Our observations are reported in Table 1.
Notes and references
1 (a) S. Nagarajan and B. Ganem, J. Org. Chem., 1987, 52, 5044;
(b) J. E. Wrobel and B. Ganem, Tetrahedron Lett., 1981, 22, 3447.
2 D. C. Tahmassebi and T. Sasaki, J. Org. Chem., 1998, 63, 728;
(b) G. Lewin and C. Schaeffer, Heterocycles, 1998, 48, 171;
(c) G. J. Rowlands, D. Craig and P. S. Jones, Chem. Commun., 1997,
2141.
3 B. C. Ranu, A. Majee and A. Sarkar, J. Org. Chem., 1998, 63, 370.
4 R. C. Larock, Comprehensive organic transformations, VCH,
New York, 1989, 421.
5 R. F. Borch, M. D. Bernstein and H. D. Durst, J. Am. Chem. Soc.,
1971, 93, 2897.
6 A. Pelter, R. M. Rosser and S. Mills, J. Chem. Soc., Perkin Trans. 1,
1984, 717.
7 N. M. Yoon, E. G. Kim, H. S. Son and J. Choi, Synth. Commun.,
1993, 23, 1595.
8 G. Verardo, A. G. Giumanini, P. Strazzolini and M. Poiana,
Synthesis, 1993, 121.
It is clear from Table 1 that both aliphatic and aromatic
primary amines react with aromatic aldehydes as well as
ketones to give an appreciable yield of the corresponding
secondary amines, but the secondary amines (e.g. piperidine)
remain inert in this system. Moreover acetophenone and benzo-
phenone also remained unreactive with n-butylamine. In the
case of p-nitrobenzaldehyde, reduction of the aromatic nitro
group was also observed, giving a mixture of products. Unlike
sodium triacetoxyborohydride, nickel boride is also well suited
to α,β-unsaturated ketones.
9 I. V. Micovic, M. D. Ivanovic, D. M. Paitak and V. D. Bojic,
Synthesis, 1991, 1043.
10 S. Bhattacharyya, A. Chatterjee and S. K. Duttachowdhury,
J. Chem. Soc., Perkin Trans. 1, 1994, 1.
11 R. J. Mattson, K. M. Pham, D. J. Leuck and K. A. Cowen, J. Org.
Chem., 1990, 55, 2552.
12 J. Brussee, R. A. T. M. van Benthem, C. G. Krusse and A. van der
Gen, Tetrahedron: Asymmetry, 1990, 1, 163.
13 S. Kim, C. H. Oh, J. S. Ko, K. H. Ahn and Y. J. Kim, J. Org. Chem.,
1985, 50, 1927.
14 A. F. Abdel-Magid, K. G. Carson, B. D. Harris, C. A. Maryanoff
and R. D. Shah, J. Org. Chem., 1996, 61, 3849.
15 (a) C. T. Bui, F. A. Rasoul, F. Ercole, Y. Pham and N. J. Maeji,
Tetrahedron Lett., 1998, 39, 9283; (b) E. G. Brown and M. J. Nass,
Tetrahedron Lett., 1997, 38, 8457.
Experimental
To a solution of 1.6 mmol (379 mg) of nickel chloride hexa-
hydrate in 3 ml of methanol was added 3 mmol (111 mg) of
sodium borohydride under stirring at rt. Formation of nickel
boride was indicated by instant indication of black precipitate
with evolution of gases. Immediately a premixed solution of 1
mmol of aldehyde/ketone and 1.5 mmol of amine in 2 ml of
methanol was added. Stirring was continued at rt with inter-
mittent monitoring by TLC. On completion the reaction
mixture was diluted with chloroform (25 ml) and filtered.
The precipitate was washed well with chloroform (3 × 10 ml).
The combined organic layer was washed with water, dried
over anhydrous sodium sulfate and evaporated at reduced pres-
sure to get the crude product. Purification was performed by
preparative TLC if needed.
16 J. C. Sarma and R. P. Sharma, Chem. Ind. (London), 1987, 764.
17 H. C. Brown and C. A. Brown, J. Am. Chem. Soc., 1962, 84, 1493.
18 H. H. Seltzman and B. D. Berrang, Tetrahedron Lett., 1993, 34,
3083.
19 R. H. Khan and R. C. Rastogi, Indian J. Chem., 1993, 32B, 898.
20 M. Yale, C. Keen, N. A. Bell, P. K. P. Drew and M. Coke, Appl.
Organomet. Chem., 1995, 9, 297.
21 S. S. Zaman, J. C. Sarma and R. P. Sharma, Chem. Ind. (London),
1991, 509.
22 G. M. Singhal, J. C. Sarma and R. P. Sharma, Indian J. Chem., 1989,
28B, 853.
23 D. N. Sarma and R. P. Sharma, Tetrahedron Lett., 1985, 26, 2581.
24 W. S. Emerson, Org. React., 1984, 4, 174.
Communication a909770h
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J. Chem. Soc., Perkin Trans. 1, 2000, 503–504
Saxena, Ira
