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J IRAN CHEM SOC (2013) 10:181–188
Indion 190 resin [22] are also employed for the N-Boc
protection. However, despite the potential utility of these
catalysts, many of these methodologies are associated with
several shortcomings such as extended reaction time, ele-
vated temperatures, tedious work-up, using anhydrous
organic solvents, reaction under oxidizing conditions, using
strong acids, low yields, harsh reaction conditions, diffi-
culty in the preparation and moisture sensitivity of the
catalysts, high cost and high toxicity of the reagents, non-
recyclability of the catalyst, and formation of side-products
such as isocyanates, poly-acylated products, urea and N,
N-di-Boc derivatives. Therefore, there is a need to develop
an alternative method for the N-Boc protection of amines.
linked with 2 % DVB *60 mesh, MW: 60,000; Fluka
Chemical] in 10 mL dry CH2Cl2 over a period of 5 min.
The mixture was stirred at room temperature for 6 h and
then dichloromethane was removed under reduced pressure.
The solid powder was dried under vacuum at 65 °C for 48 h
to afford NSPVPC (6.53 g) as a pale yellow powder.
General procedure for the synthesis of N-tert-
butylcarbamates
Amine (1 mmol) was added to a magnetically stirred
mixture of (Boc)2O (1 mmol) and NSPVPC (5 mg). After
completion of the reaction (monitored by TLC), ethyl
acetate (15 mL) was added to the reaction mixture and the
catalyst was recovered by filtration and washed with ethyl
acetate (2 9 5 mL) and dried. The product was purified by
column chromatography, using ethyl acetate–petroleum
ether (2:8) as eluent.
Experiment
Materials
Chemicals were purchased from Fluka, Merck, and Aldrich
chemical companies. All yields refer to the isolated prod-
ucts. Products were characterized by their physical and
spectroscopic data and comparison with authentic samples.
The purity determination of the substrate and reaction
monitoring were accompanied by thin layer chromatogra-
phy (TLC) on silica-gel polygram SILG-UV254 plates.
Spectral data of the selected products
8b: Brown solid, m.p. 52–54 °C; IR (KBr): m = 3,320,
2,990, 2,920, 1,690, 1,600, 1,530, 1,450, 1,420, 1,362,
1,285, 1,240, 1,160, 1,045, 1,032, 960, 870, 842 cm-1; H
1
NMR (CDCl3, 400 MHz): d 1.55 (s, 9H), 3.82 (s, 3H), 6.61
(dd, J = 8.0 and 8.4 Hz, 1H), 6.64 (br s, 1H), 6.87 (d, J =
8.0 Hz, 1H), 7.14 (s, 1H), 9.19 (dd, J = 8.0 and 8.4 Hz,
1H) ppm; 13C NMR (CDCl3, 100 MHz): d 28.4, 55.3, 80.5,
104.1, 108.9, 110.7, 129.7, 139.7, 152.7, 160.3 ppm.
13b: White solid, m.p. 99–101 °C; IR (KBr): m = 3,310,
3,300, 3,110, 3,090, 2,990, 1,773, 1,710, 1,650, 1,540,
1,446, 1,278, 1,250, 1,222, 1,150, 1,112, 1,080,
Instrumentation
IR spectra were run on a Perkin-Elmer bio-spectrometer.
The reaction conversions were measured by GC on a
1
Shimadzu model GC-16A instrument. The H NMR (300
or 400 MHz) and 13C NMR (75 or 100 MHz) were run on
a Bruker Avance DPX-250, FT-NMR spectrometer (d in
ppm). Microanalyses were performed on a Perkin-Elmer
240-B microanalyzer. Melting points were recorded on a
Bu¨chi B-545 apparatus in open capillary tubes. X-ray dif-
fraction (XRD) measurements were performed at room
temperature on a Philips PW1830 generator X-ray powder
diffractometer, using Ni filter and Cu-Ka radiation
1,045 cm-1; H NMR (DMSO-d6, 300 MHz): d 1.63 (s,
1
9H), 7.31–7.52 (m, 4H), 11.7(s, 1H) ppm; 13C NMR
(DMSO-d6, 75 MHz): d 28.3, 87.8, 113.4, 123.5, 125.1,
127.9, 133.8, 147.7, 161.5, 167.5 ppm.
15b: Off-white solid; m.p. 72–73 °C; IR (KBr):
m = 3,395, 2,980, 2,920, 1,680, 1,600, 1,508, 1,360, 1,320,
1,295, 1,260, 1,172, 1,000, 858, 761, 694 cm-1; H NMR
1
(CDCl3, 400 MHz): d = 1.50 (s, 9H), 2.36 (s, 3H), 4.30 (d,
J = 5.2, 2H), 4.88 (br s, 1H), 7.16 (d, J = 7.6 Hz, 2H), 7.20
(d, J = 8.0 Hz, 2H) ppm; 13C NMR (CDCl3, 100 MHz): d =
21.1, 28.4, 44.5, 79.4, 127.5, 129.3, 135.9, 137.0, 155.9 ppm.
16b: Colorless oil; IR (KBr): m = 3,390, 2,988, 2,930,
1,686, 1,610, 1,508, 1,358, 1,317, 1,289, 1,258, 1,170, 998,
855 cm-1; 1H NMR (CDCl3, 400 MHz): d = 1.50 (s, 9H),
1.83 (qin, J = 7.2, 7.6 Hz, 2H), 2.67 (dd, J = 7.6 and 8.0,
2H), 3.18 (d, J = 6.0 Hz, 2H), 7.22 (dd, J = 5.6 and
7.6 Hz, 3H), 7.32 (d, J = 8.0 Hz, 2H) ppm; 13C NMR
(CDCl3, 100 MHz): d = 28.5, 31.8, 33.2, 40.3, 125.9,
128.40, 128.44, 141.6, 156.1 ppm.
˚
(k = 1.542 A). The scanning was over a range of
2h = 10–70°. TGA and SEM analyses were performed on
Polymer Laboratories TGA-PL thermal analysis instrument
(heating rate of 10 °C/min) and on a Quanta 200 micro-
scope (the samples were coated with gold powder on 682
Gatan Inc.), respectively. All measurements were con-
ducted under nitrogen.
Catalyst preparation
Chlorosulfonic acid (1.5 mL, 22 mmol, as a [97 % stan-
dard solution) was added to a suspension of powdered
poly(4-vinylpyridine) (5.0 g) [Poly(4-vinylpyridine) cross-
18b: Out-white solid; m.p. 57–59 °C; IR (KBr):
m = 3,320, 2,910, 2,860, 1,680, 1,520, 1,450, 1,360, 1,317,
123