2
032
H. Alinezhad et al.
with electron-withdrawing groups which is not possible with [NaBH CN] [6] and
3
[
NaBH(OAc) ] [4], the most often used reagents for this purpose (Table 1; Entries
3
13, 14).
It is also interesting to mention that in other methods [3–5], a strong acidic
medium is applied whereas in our procedure we do not use any acid, and the
reaction conditions are very mild. Thus, it can be used for acid sensitive substrates.
The reducing agent is also a good substitute for Na[BH(OAc) ] and Na[BH CN]
3
3
for the preparation of amines by reductive amination of carbonyl compounds under
neutral conditions. The use of NaBH eliminates the problems encountered by
4
Na[BH CN], such as residual cyanide in the product and in the waste stream,
3
and by using Na[BH(OAc) ] in the presence of acetic acid, which is corrosive
3
and also suffers from moderate yields of the amine products and long reaction
times [4, 6].
In conclusion, although there are several methods available for this transforma-
tion, we believe that the present method offers considerable advantages in terms of
simplicity, commercially available reagents, mildness of the reaction medium, easy
reaction work up, efficiency, chemoselectivity, high reaction rates and yields, low
toxicity of the reagent, and no pH adjustment.
Experimental
NaBH and carbonyl compounds were purchased from Merck. All products were identified by com-
4
1
parison of their spectra ( H NMR, IR) and physical data with those of authentic samples. Yields refer
1
to isolated products. IR spectra were determined on a Shimadzu instrument. H NMR spectra were
recorded with Bruker DRX500 AVANCE (500MHz) and GNM-Ex90A (90 MHz) spectrometers, using
CDCl as solvent.
3
General Procedure for the Amination of Aldehydes and Ketones
to their Corresponding Amines with NaBH in Micellar Media
4
To a stirred solution of 1 mmol carbonyl compound and 4 mmol primary amine or 2 mmol secondary
3
amine in 7 cm aqueous CTAB solution (cmc), NaBH was added in 0.5 mmol portions (0.019 g) every
4
3
h until the reaction showed by TLC (eluent: n-hexane=EtOAc¼ 8=1–10=1) to be complete. The
3
mixture was stirred for the time specified in Table 1 and was extracted with 3ꢂ20 cm Et O. The
2
organic layers were combined and washed with H O, brine, dried (MgSO ), and then the solvent was
4
2
evaporated. The resulting mass was applied to a silica gel column and eluted with n-hexane=EtOAc
10=1–16=1). Evaporation of the solvent afforded the pure amines in 84–96% yields (Table 1).
(
Acknowledgement
Financial support of this work from the Research Council of Mazandaran University is gratefully
acknowledged. We also thank A. Kiani, Z. Naderi, and O. Ropani for their assistance.
References
[
[
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(1984) J Chem Soc Perkin Trans 1, 717
[3] a) Bhattacharyya S, Chatterjee A, Williamson JS (1995) Synlett 1079; b) Neidigh KA, Avery
MA, Williamson JS, Bhattacharyya S (1998) J Chem Soc Perkin Trans 1: 2527