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B.S. Takale et al. / Tetrahedron xxx (2014) 1e5
3. Conclusions
J¼7.2 Hz, 1H), 6.57 (dd, J1¼8.4 Hz, J2¼1.2 Hz, 2H), 4.48 (q, J¼6.8 Hz,
1H), 4.02 (br s, 1H), 1.51 (d, J¼6.8 Hz, 3H).
In conclusion, we have described highly chemoselective re-
duction of ketimines using AuNPore/PhMe2SiH/H2O system. The
respective amines could be achieved in high chemical yields under
mild conditions. Accordingly, this reducing system may provide
a new and selective procedure for reductive amination of aldehydes
and ketones.
4.3.2. N-(1-(4-Methoxyphenyl)ethyl)aniline
(400 MHz, CDCl3)
(2b).13 1H
NMR
d
7.28 (d, J¼8.8 Hz, 2H), 7.09 (t, J¼8.8 Hz, 2H), 6.85
(d, J¼8.8 Hz, 2H), 6.63 (t, J¼7.6 Hz, 1H), 6.51 (d, J¼8.0 Hz, 2H), 4.44
(q, J¼6.8 Hz, 1H), 3.98 (br s, 1H), 1.49 (d, J¼6.8 Hz, 3H).
4.3.3. N-(1-(4-Bromophenyl)ethyl)aniline
(400 MHz, CDCl3)
7.08 (t, J¼8.0 Hz, 2H), 6.65 (t, J¼7.6 Hz, 2H), 6.46 (d,
J¼8.4 Hz, 1H), 4.42 (q, J¼6.8 Hz, 1H), 3.98 (br s, 1H), 1.47 (d,
J¼6.8 Hz, 3H).
(2c).12 1H
NMR
d
7.42 (d, J¼8.0 Hz, 2H), 7.23 (d, J¼8.8 Hz, 2H),
4. Experimental section
4.1. Preparation of AuNPore catalyst
4.3.4. N-Phenyl-1,2,3,4-tetrahydronaphthalen-1-amine
NMR (400 MHz, CDCl3) 7.43e7.40 (m, 1H), 7.24e7.14 (m, 5H),
(2d).14 1H
The AuNPore catalyst was prepared by minor change of the re-
ported procedure.6c Gold (99.99%) and silver (99.99%) were melted
at high temperature with the help of electric arc-melting furnace
under Ar atmosphere. The resultant Au30Ag70 alloy (30:70, in at. %),
d
6.74e6.68 (m, 3H), 4.65 (q, J¼4.8 Hz, 1H), 3.89 (br s, 1H), 2.88e2.78
(m, 2H), 2.02e1.81 (m, 4H).
was rolled down to thickness of 40e60 mm. Further, this foil was
4.3.5. N-(1-(Naphthalen-1-yl)ethyl)aniline
(400 MHz, CDCl3)
(d, J¼8.4 Hz, 1H), 7.65 (d, J¼7.2 Hz, 1H), 7.58e7.49 (m, 2H), 7.40 (t,
J¼7.6 Hz, 1H), 7.06 (t, J¼8.0 Hz, 2H), 6.63 (t, J¼7.6 Hz, 1H), 6.48 (dd,
J1¼8.4 Hz, J2¼0.8 Hz, 2H), 5.28 (q, J¼6.8 Hz, 1H), 4.16 (br s, 1H), 1.66
(d, J¼6.8 Hz, 3H).
(2e).12 1H
NMR
annealed at 850 ꢀC for 20 h and cut into small pieces (5ꢂ2 mm
square). Treatment of the resulting pieces (50 mg) with 70 wt %
nitric acid (50 mL) at room temperature for 18 h led to the for-
mation of the nanoporous skeleton through selective de-alloying of
silver. The copper colored pieces were washed with a saturated
aqueous solution of NaHCO3, distilled water, and acetone, succes-
sively. Drying the resultant material under vacuum gave the
nanoporous gold with composition Auw100Ag0 as calculated from
the weight loss of silver.
d
8.16 (d, J¼8.4 Hz, 1H), 7.90 (d, J¼8.4 Hz, 1H), 7.74
4.3.6. N-Benzhydrylaniline (2f).15 1H NMR (400 MHz, CDCl3)
d
7.34e7.19 (m, 10H), 7.07 (t, J¼7.6 Hz, 2H), 6.66 (t, J¼7.6 Hz, 1H),
6.50 (d, J¼8.0 Hz, 2H), 5.47 (s, 1H), 4.18 (s, 1H).
4.3.7. 4-Methoxy-N-(1-phenylethyl)aniline
(2g).2c 1H
NMR
4.2. General methods and materials
(400 MHz, CDCl3)
d
7.37e7.21 (m, 5H), 6.68 (d, J¼8.8 Hz, 2H), 6.46
1H and 13C NMR spectra were recorded on either a Varian Inova-
400 spectrometer (400 MHz for 1H, 100 MHz for 13C) or a Bruker
Avance II-400 spectrometer (400 MHz for 1H, 100 MHz for 13C);
DMSO-d6 and CDCl3 were used as a solvent, while TMS was used as
an internal standard, The chemical shifts are reported in parts per
(d, J¼9.2 Hz, 2H), 4.41 (q, J¼6.8 Hz, 1H), 3.78 (br s, 1H), 3.69 (s, 3H),
1.49 (d, J¼6.8 Hz, 3H).
4.3.8. 4-Methyl-N-(1-phenylethyl)aniline
(400 MHz, CDCl3)
(d, J¼8.4 Hz, 2H), 4.44 (q, J¼6.8 Hz, 1H), 3.92 (br s, 1H), 2.17 (s, 3H),
1.49 (d, J¼6.4 Hz, 3H).
(2h).2c 1H
NMR
d
7.37e7.19 (m, 5H), 6.89 (d, J¼8.0 Hz, 2H), 6.43
million downfield (d) from TMS, the coupling constants J are given
in Hertz. The peak patterns are indicated as follows: br s, broad
singlet; s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet. IR
spectra were recorded on an NEXUS FTIR spectrometer. TLC was
carried out on SiO2 (silica gel 60 F254, Merck) plates. Solvents were
obtained and used without previous purification. All of the other
reactants were obtained and also used without any previous
treatment.
4.3.9. N-(1-Phenylethyl)butan-1-amine (2i).16 1H NMR (400 MHz,
CDCl3)
d
7.31e7.20 (m, 5H), 3.74 (q, J¼6.8 Hz, 1H), 2.42 (m, 2H), 1.44
(m, 2H), 1.34 (d, J¼6.4 Hz, 3H), 1.29 (m, 2H); 0.87 (t, J¼7.2 Hz, 3H).
4.3.10. N-(1-(Thiophen-2-yl)ethyl)aniline (2j).17 1H NMR (400 MHz,
CDCl3)
d
7.40 (d, J¼8.0 Hz, 1H), 7.33e7.29 (m, 3H), 7.24e7.22 (m,
1H), 6.98 (d, J¼8.0 Hz, 1H), 6.49 (t, J¼7.6 Hz, 1H), 6.37 (d,
J¼8.0 Hz, 1H), 4.70 (br s, 1H), 4.52 (q, J¼6.4 Hz, 1H), 1.57 (d,
J¼6.8 Hz, 3H).
4.3. General procedure for reduction ketimine (1a) using
AuNPore catalyst
In acetonitrile solution (2 mL) were added AuNPore (2 mol %),
imine 1a (0.5 mmol), PhMe2SiH (0.6 mmol), H2O (0.6 mmol)
successively at 50 ꢀC in a V-shaped reactor. The reaction mixture
was stirred at 50 ꢀC for 5 h and was monitored by thin layer
chromatography (TLC). Later, the solution was taken out from the
V-shaped reactor with the help of pipette and the reactor was
washed three times with acetone. The combined organic solution
was evaporated to give the crude product, which was purified by
silica gel column chromatography using pet ether/ethyl acetate
(20:1) as an eluent to obtain pure product; amine 2a was obtained
in 94% yield.
4.4. Reductive amination using AuNPore catalyst
In acetonitrile solution (2 mL) were added AuNPore (5 mol %),
benzaldehyde 4a (R1¼Ph; 0.5 mmol) aniline 9a (R2¼H; 0.5 mmol),
PhMe2SiH (0.6 mmol) successively at room temperature in a V-
shaped reactor. The reaction mixture was stirred at 80 ꢀC for 5 h and
was monitored by Thin Layer Chromatography (TLC). Later, the
solution was taken out from the V-shaped reactor with the help of
pipette and the reactor was washed three times with acetone.
Collective organic solution was evaporated to give crude product,
which was purified by silica gel column chromatography using pet
ether/ethyl acetate (20:1) as an eluent to obtain pure product 6a in
69% yield.
4.3.1. N-(1-Phenylethyl)aniline (2a).12 1H NMR (400 MHz, CDCl3)
d
7.38e7.29 (m, 4H), 7.24e7.20 (m, 1H), 7.10e7.06 (m, 2H), 6.63 (t,