Synthesis of novel functionalized N-tosylaldimines

Article abstract of DOI:10.1081/SCC-120015720

Condensation of a variety of aromatic aldehydes with p-toluenesulfonamide in the presence of Lewis acids affords novel functionally varied aromatic N-tosylaldimines in good yields. A diverse array of aromatic aldehydes was examined, each containing a uniq

Full text of DOI:10.1081/SCC-120015720

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Synthesis of Novel Functionalized N -Tosylaldimines
James H. Wynne a , Stacy E. Price a , Jeffrey R. Rorer a & Wayne M. Stalick a b
a Department of Chemistry, George Mason University, Fairfax, Virginia, USA
b Department of Chemistry, George Mason University, 4400 University Drive, Fairfax, VA
22030, USA
Version of record first published: 21 Aug 2006.
To cite this article: James H. Wynne , Stacy E. Price , Jeffrey R. Rorer & Wayne M. Stalick (2003): Synthesis of Novel
Functionalized N -Tosylaldimines, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 33:2, 341-352
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 2, pp. 341–352, 2003
Synthesis of Novel Functionalized
N-Tosylaldimines
James H. Wynne, Stacy E. Price, Jeffrey R. Rorer,
*
and Wayne M. Stalick
Department of Chemistry, George Mason University,
Fairfax, Virginia, USA
ABSTRACT
Condensation of a variety of aromatic aldehydes with p-toluenesul-
fonamide in the presence of Lewis acids affords novel functionally
varied aromatic N-tosylaldimines in good yields. A diverse array of
aromatic aldehydes was examined, each containing a unique func-
tionality. The new method reported here allows for incorporation of
functionalities that are unavailable by existing methods.
Key Words: N-Tosylaldimines; Aldehydes; Lewis acid.
*Correspondence: Wayne M. Stalick, Department of Chemistry, 4400 University
Drive, George Mason University, Fairfax, VA 22030, USA. Fax: 703-993-1055.
E-mail: wstalick@gmu.edu.
341
DOI: 10.1081/SCC-120015720
Copyright & 2003 by Marcel Dekker, Inc.
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Wynne et al.
INTRODUCTION
The growing interest in N-tosylaldimines is apparent from the
numerous recent reports in the literature.[1] Not only does this class of
compound offer stability when stored for prolonged periods of time, but
N-tosylaldimines also function as novel synthons for the facile introduc-
tion of diverse functionalities in an efficient single step, when employed as
electrophiles.[1b,2] Likewise, when employed as dieneophiles, imines also
offer an easy method for controlling chemo and regioselectivity in many
[4þ2], [3þ2], and even [2þ2] cycloadditions.[3] Despite the numerous
reported methods currently available for the synthesis of tosylaldimines,
many proceed under non-neutral conditions, extreme thermal conditions,
or they are low yielding reactions.[4–5] The limited availability of these
tosylaldimines is evident by the small number of substrates examined in
the aforementioned reports.[2–3]
Our lab also had a need for tosylaldimines possessing additional
functionalities, thus, it became our goal to determine how great a variety
of functionality could be incorporated into the imine. These imines are
novel synthons, which we plan to use in a combinatorial matrix to afford
a variety of highly functional biologically active compounds. These com-
pounds, g-carbolines, require the incorporation of additional biological
binding ability through the introduction of groups containing hydroxy-,
trifluoromethyl-, nitro-, and other functionalities, which were therefore
incorporated into the tosylaldimines.
RESULTS AND DISCUSSION
Our initial attempts for condensing a variety of aromatic aldehydes
with p-toluene sulfonamide in toluene without the addition of a Lewis
acid, yielded success with only two substrates (Entries 1 and 4) (Method
A) (Fig. 1). Unidentifiable products resulted for those aldehydes contain-
ing sensitive functionalities due to the prolonged thermal conditions
employed. We next examined the method reported by Love,[5] which
allows the efficient introduction of pH sensitive substrates in high yields,
under relatively mild conditions. The method was effective for a couple of
additional substrates not reported by Love, Table 1 (Compounds 3b and
c); however, it gave either unacceptable yields or a mixture of products for
the other aldehydes examined. The wide variety of functionally diverse
products required for our studies was synthesized only after necessary
modifications to the original reaction conditions were made (Method B).

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Novel Functionalized N-Tosylaldimines
343
Figure 1. Methods for formation of N-tosylaldimines.
Several factors were examined to determine their effect on the
conversions of the more sensitive functionalities. For Entries
(5, 7–13, 16) it was observed that when the reaction mixture was heated
to elevated temperatures i.e., greater than the usual 140–160ꢀC range,
there was additional formation of unidentifiable product. Likewise, pro-
longed heating beyond the 4 h period (Entries 8 and 9) provided for a
constant amount of product formation but this was accompanied by
increasing amounts of unidentifiable product, thus making isolation
more difficult. The use of a longer or air-jacketed still head also forced
elevated reaction flask temperatures that produced the concomitant
decrease in product yield as described above. Finally, changes to the
methods of isolation and purification did offer a positive correlation
with yield. It was found that isolation by precipitation and repetitive
washings with cold ether afforded higher yields and products of sufficient
purity (>95%) for subsequent reactions. Additionally, flash column
chromatography, when used, gave lower yields and attempts to purify
the imines employing silica gel frequently resulted in hydrolysis into the
respective aldehyde and sulfonamide. Employing neutral alumina also
significantly diminished the yields.
Caution: An explosion of the reaction vessel occurred using any of
the previously reported methods employing tetraethyl orthosilicate with
2,4-dinitrobenzaldehyde upon heating to temperatures greater than
150ꢀC; at lower temperatures no product was formed. Likewise,
3-indolecarboxaldehyde afforded no desired product employing meth-
ods A or B. For these two compounds, method C, was developed; it
substitutes titanium(IV) chloride for tetraethyl orthosilicate followed by
the azeotropic removal of water:benzene. This method affords good
yields in a safer manner, thus reducing the risk of explosion in the
case of 3n and other similar compounds. Neither tetraethyl orthosili-
cate, PPA, nor ZnCl2 yielded product when used as the Lewis acid;
however, titanium(IV) chloride proved to be active and safe allowing

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Novel Functionalized N-Tosylaldimines
345

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Wynne et al.
the reaction to proceed at lower temperatures. Using an aldehyde that
was active to all three methods, benzaldehyde, showed comparable
yields and reaction times for the acid promoted conditions (Entries
1–3). Method C was thus the only successful procedure for making
compounds 3n and 3o and it proceeded under milder conditions
giving comparable or better yields to method B in all other trials
(Entries 3, 6, 17, 19).
We have synthesized a variety of N-tosylaldimines previously unre-
ported in the literature employing a couple of efficient methods. A new
safer method for unstable or unreactive substrates was developed and
its yields compared favorably with previous methods. A wide variety
of aromatic aldehydes containing either electron donating or electron
withdrawing groups were successfully employed. These easy, high
yielding methods for aldimine synthesis should provide a wider
variety of starting materials for studies like those discussed in the
introduction.
EXPERIMENTAL
Melting points were determined on a Thomas Hoover melting point
apparatus and are uncorrected. 1H and 13C NMR spectra were taken on a
Bruker DPX 300 spectrometer, recorded at 300 MHz and 75 MHz respec-
tively with TMS as an internal standard. Chemical shifts are reported in
units of ppmdownfield fromTMS. Coupling constants, J, are reported in
units of Hertz (Hz). FTIR spectra were recorded on a Perkin–Elmer
Paragon 1000 spectrometer. GC analyses were performed on a
Hewlett–Packard 6890 capillary chromatograph with FID (0.32 mm Â
30 mHP-5, 0.25 mm, column programmed to hold 100ꢀC for 1 min with
a 20ꢀC/min ramp to 250ꢀC). Elemental analyses were performed on a
Perkin–Elmer Series II, C, H, N-Analyzer Model 2400. Unless otherwise
stated, chemicals were reagent grade and were obtained from commercial
sources and were used without further purification. All moisture-sensitive
reactions and reagent transfers were carried out under nitrogen. Thin
layer chromatography (TLC) was performed on Eastman Kodak pre-
coated silica gel sheets with glass backing. Preparative column chroma-
tography was performed using an ISCO model Sg100c combi-flash
systememploying silica gel, 60A (200–400 mesh). Purification of all new,
previously unreported compounds for characterization was accomplished
through repetitive recrystallizations.

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Novel Functionalized N-Tosylaldimines
Preparation
347
General Method A
p-Toluenesulfonamide (9.16 mmol), 25 mL of toluene and the respec-
tive aldehyde (1a–b) (9.14 mmol), were combined in a 50 mL round-
bottomed flask equipped with a magnetic stirrer, a positive flow of
nitrogen and a Dean-Stark trap with condenser. The reaction mixture
was heated at reflux for 25 h, with azeotropic removal of water. The
reaction mixture was allowed to cool to room temperature, followed by
concentration on the rotary evaporator. Crude product purification was
performed by recrystallization with diisopropyl ether (50 mL) to afford
the desired imines (3a–b).
General Method B
p-Toluenesulfonamide (17.42 mmol) and tetraethyl orthosilicate
(19.17 mmol) were combined with the respective aldehyde (1b–m)
(17.42 mmol) in a 50 mL round-bottomed flask equipped with a magnetic
stirrer, a positive flow of argon and a short still head (Approx. 3–4 cm
length), connected to a receiving flask. The reaction mixture was heated
at 140–160ꢀC, and ethanol, upon formation, was collected in the receiv-
ing flask. After cooling, the reaction mixture was diluted with ether,
suction filtered and the precipitate washed with cold Et2O (3 Â 15 mL).
The resulting powder was dried under vacuumand recrystallized to
afford 3b–m in the desired purity.
General Method C
An equimolar aliquot (3.18 mmol) of p-toluenesulfonamide, the
respective aldehyde, titanium(IV) chloride (1M in THF), and 40 mL of
benzene were combined in a 100 mL round-bottomed flask equipped with
a magnetic stirrer and a 5 mL capacity Dean-Stark trap with condenser.
Under a positive flow of nitrogen, the reaction mixture was allowed to
reflux rapidly with azeotropic removal of water for 8–12 h. After slowly
cooling to roomtemperature, the solvent was evaporated under reduced
pressure and the residue was dissolved in 50 mL of CH2Cl2 and washed
with H2O (3 Â 30 mL). The organic layer was dried over MgSO4, and

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348
Wynne et al.
concentrated on a rotary evaporator. The crude product was purified by
recrystallization fromEt O to afford compounds 3a,b,l–o.
2
Characterization
N-Benzylidene-4-methyl-benzenesulfonamide (3a): White powder,
m.p. 110–111ꢀC [lit.[6] 109ꢀC]. FTIR: 3259, 1597, 1446, 1301, 1223,
1
1156, 1088, and 21.50 cmÀ1. H NMR: 9.04 (s, 1H), 7.94–7.88 (m, 3H),
7.81 (d, J ¼ 9, 2H), 7.49 (d, J ¼ 9, 2H), 7.34 (t, J ¼ 6, 2H), 2.44 ꢀ (s, 3H).
13C NMR: 192.42, 143.57, 134.90, 131.30, 130.10, 129.69, 129.51, 129.13,
126.45, 21.50 ꢀ.
N-(4-Chlorobenzylidene)-4-methyl-benzenesulfonamide (3b): White
needles, m.p. 173–175ꢀC [lit.[7] 174–175ꢀC]. FTIR: 3040, 1607, 1587,
1
1560, 1400, 1317, 1161, 1083, 1010, and 803 cmÀ1. H NMR: 8.99 (s,
1H), 7.88 (dd, J ¼ 9, 4H), 7.48 (d, J ¼ 9, 2H), 7.36 (d, J ¼ 9, 2H), 2.45 ꢀ
(s, 3H). 13C NMR: 169.01, 145.19, 141.88, 135.38, 132.76, 131.28, 130.27,
130.03, 128.57, 22.08 ꢀ.
4-Methyl-N-(2-trifluoromethyl-benzylidene)-benzenesulfonamide (3c):
Pale green powder, m.p. 97–98ꢀC. FTIR: 1638, 1529, 1446, 1303, 1160,
1
1125, 1093, 1093, 1062, and 1036 cmÀ1. H NMR: 9.34 (s, 1H), 8.33 (d,
J ¼ 6, 1H), 7.89 (d, J ¼ 9, 2H), 7.81–7.76 (m, 2H), 7.76–7.64 (m, 2H), 7.36
(d, J ¼ 9, 2H), 7.30 (d, J ¼ 3, 1H), 2.44 ꢀ (s, 3H). 13C NMR: 166.07,
166.07, 145.07, 143.83, 133.93, 132.32, 129.95, 129.72, 128.41, 126.48,
126.33, 112.91, 21.66 ꢀ. Anal. Calcd. for C15H12F3NO2S: C, 55.04; H,
3.70; N, 4.28. Found: C, 55.12; H, 3.59; N, 4.13.
N-(4-Hydroxy-benzylidene)-4-methyl-benzenesulfonamide (3d): Pink
powder, m.p. 109–111ꢀC. FTIR: 3352, 3248, 1586, 1441, 1301, 1156,
and 1088 cmÀ1
.
1H NMR: 9.85 (s, 1H), 7.81 (d, J ¼ 9, 2H), 7.76 (d,
J ¼ 6, 2H), 7.37 (d, J ¼ 6, 2H), 7.01 (d, J ¼ 9, 2H), 5.63 (bs, 1H-O),
2.94 ꢀ (s, 3H). 13C NMR: 191.38, 143.56, 133.13 (overlapping peaks),
130.51, 128.07, 127.28, 117.03, 21.67 ꢀ. Anal. Calcd. for C14H13NO3S:
C, 61.07; H, 4.76; N, 5.09. Found: C, 61.17; H, 4.67; N, 4.93.
4-Methyl-N-thiophen-2-ylmethylene-benzenesulfonamide (3e): Brown
powder, m.p. 98–103ꢀC (spectroscopic data agreed with that previously
reported in the literature).[11] FTIR: 3113, 1570, 1415, 1322, 1394, 1250,
1
1151, 1088, 1046, and 1021 cmÀ1. H NMR: 9.11 (s, 1H), 7.87 (d, J ¼ 8,
2H), 7.78–7.77 (m, 2H), 7.34 (d, J ¼ 8, 2H), 7.21 (t, J ¼ 4, 1H), 2.44 ꢀ (s,
3H). 13C NMR: 162.18, 144.43, 138.90, 136.63, 135.50, 129.76, 128.82,
127.97, 126.49, 21.61 ꢀ.

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Novel Functionalized N-Tosylaldimines
349
N-(2-Hydroxy-5-nitrobenzylidene)-4-methyl-benzenesulfonamide (3f ):
Yellow powder, m.p. 190–193ꢀC. FTIR: 3414, 1638, 1342, 1285, 1161,
1
and 1072 cmÀ1. H NMR: 9.15 (s, 1H), 8.50 (s, 1H), 8.37 (d, J ¼ 9, 1H),
7.88 (d, J ¼ 8.1, 2H), 7.40 (d, J ¼ 8.4, 2H), 7.13 (d, J ¼ 9, 1H), 2.47 ꢀ (s,
3H). 13C NMR: 169.77, 166.35, 145.88, 140.84, 133.88, 131.42, 130.29,
129.73, 128.28, 119.07, 115.86, 21.75 ꢀ. Anal. Calcd. for C14H12N2O5S: C,
52.49; H, 3.78; N, 8.75. Found: C, 52.67; H, 3.72; N, 8.49.
N-(2-Hydroxy-naphthalene-1-ylmethylene)-4-methylbenzenesulfonamide
(3g): Orange powder, m.p. 164–166ꢀC. FTIR: 3425, 1623, 1597, 1550,
.
1461, 1311, 1156, 1083, 969, and 828 cmÀ1 1H NMR: 10.02 (s, 1H),
8.24 (d, J ¼ 9, 1H), 7.98 (d, J ¼ 9, 1H), 7.90 (d, J ¼ 12, 2H), 7.80 (d,
J ¼ 9, 1H), 7.68–7.62 (m, 1H), 7.49–7.43 (m, 1H), 7.36 (d, J ¼ 6, 1H),
7.15 (d, J ¼ 9, 1H), 2.45 ꢀ (s, 3H). 13C NMR: 165.43, 144.81, 139.65,
135.72, 130.00, 129.57, 129.34, 128.09, 127.79, 126.81, 124.81, 119.67,
119.20, 108.02, 21.66 ꢀ. Anal. Calcd. for C18H15NO3S: C, 66.44; H,
4.65; N, 4.30. Found: C, 66.08; H, 4.92; N, 4.23.
4-Methyl-N-(2-nitro-benzylidene)-benzenesulfonamide (3h): Yellow
powder, m.p. 133–136ꢀC [lit.[8] 130–132ꢀC]. FTIR: 1638, 1602, 1560,
1
1519, 1441, 1342, 1317, 1156, and 1088 cmÀ1. H NMR: 9.47 (s, 1H),
8.17–8.11 (m, 2H), 7.93 (d, J ¼ 9, 2H), 7.77–7.74 (m, 2H), 7.39 (d,
J ¼ 6, 2H), 2.46 ꢀ (s, 3H). 13C NMR: 166.65, 149.68, 145.27, 133.78,
130.59, 130.03, 129.72, 128.56, 126.49, 124.98, 126.49, 21.68 ꢀ.
N-(2,4-Dihydroxy-benzylidene)-4-methyl-benzenesulfonamide
(3i):
Orange powder, m.p. 107–108ꢀC. FTIR: 3352, 3359, 2978, 1628, 1596,
1566, 1503, 1446, 1322, 1228, 1156, and 1083 cmÀ1. 1H NMR: 8.95 (s, 1H),
7.83 (dd, 2H), 7.44–7.31 (m, 3H), 6.52–6.38 (m, 2H), 4.73 (bs, 2H), 2.44 ꢀ
(s, 3H). 13C NMR: 169.92, 164.86, 144.70, 137.76, 136.07, 127.65, 126.47,
109.71, 108.70, 103.59, 103.17, 21.61 ꢀ. Anal. Calcd. for C14H13NO4S: C,
57.72; H, 4.50; N, 4.81. Found: C, 57.89; H, 4.68; N, 4.62.
N-Anthracen-9-ylmethylene-4-methyl-benzenesulfonamide (3j): Yellow
powder, m.p. 214–217ꢀC [lit.[9] 218–219ꢀC]. FTIR: 1545, 1514, 1441,
.
1400, 1306, 1249, 1306, 1249, 1145, and 1083 cmÀ1 1H NMR: 10.47
(s, 1H), 8.98 (d, J ¼ 9, 2H), 8.72 (s, 1H), 8.08–8.00 (m, 4H), 7.69 (t,
J ¼ 6, 2H), 7.57 (t, J ¼ 6, 2H), 7.37 (d, J ¼ 9, 2H), 2.45 ꢀ (s, 3H).
13C NMR: 168.53, 144.47, 136.47, 133.16, 131.11, 129.88, 129.60,
129.53, 128.07, 126.81, 125.89, 124.23, 121.28, 21.64 ꢀ.
4-Methyl-N-(1H-pyrrol-2-ylmethylene)-benzenesulfonamide(3k):Brown
powder, m.p. 93–95ꢀC (spectroscopic data agreed with that previously
reported in the literature).[12] FTIR: 2262, 1638, 1581, 1524, 1301, 1156,
1088, and 1036 cmÀ1. 1H NMR: 8.71 (s, 1H), 7.82 (d, J ¼ 9, 2H), 7.31 (d,
J ¼ 9, 2H), 7.16 (d, J ¼ 6, 1H), 7.03 (d, J ¼ 6, 1H), 6.40 (m, 1H), 4.80 (bs,

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Wynne et al.
N-H), 2.44 ꢀ (s, 3H). 13C NMR: 157.20, 143.97, 136.34, 129.68, 128.45,
127.58, 126.46, 124.76, 112.88, 21.60 ꢀ.
4-Methyl-N-quinolin-2-ylmethylene-benzenesulfonamide (3l): Brown
platelets, m.p. 201–204ꢀC. FTIR: 3113, 1570, 1415, 1322, 1394, 1250,
1
1151, 1088, 1046, and 1021 cmÀ1. H NMR: 9.11 (s, 1H), 7.87 (d, J ¼ 8,
2H), 7.78–7.77 (m, 2H), 7.34 (d, J ¼ 8, 2H), 7.21 (t, J ¼ 4, 1H), 2.44 ꢀ
(s, 3H). 13C NMR: 162.18, 144.43, 138.90, 138.26, 136.63, 135.50, 129.76
(overlapping peaks), 128.82, 127.97, 126.49, 21.61ꢀ. Anal. Calcd. for
C17H14N2O2S: C, 65.79; H, 4.55; N, 9.03. Found: C, 65.91; H, 4.68;
N, 8.77.
4-Methyl-N-pyridin-2-ylmethylene-benzenesulfonamide (3m): Yellow
needles, m.p. 123–126ꢀC [lit.[10] 121–122ꢀC]. FTIR: 3258, 1586, 1317,
1
1166, 1145, 1083, 906, and 808 cmÀ1. H NMR: 9.86 (s, 1H), 8.61 (d,
J ¼ 6, 1H), 7.95 (d, J ¼ 9, 1H), 7.73 (t, J ¼ 9, 1H), 7.67 (d, J ¼ 9, 2H),
7.25 (d, J ¼ 9, 2H), 6.79 (t, J ¼ 6, 2H), 2.45 ꢀ (s, 3H). 13C NMR: 170.49,
161.56, 148.79, 144.09, 137.35, 130.38, 129.28, 129.01, 128.12, 124.28,
21.98 ꢀ.
N-(2,4-Dinitro-benzylidene)-4-methyl-benzenesulfonamide (3n): Gold
platelets, m.p. 149–151ꢀC. FTIR: 1592, 1535, 1405, 1343, 1161, and
1088 cmÀ1
.
1H NMR: 9.49 (s, 1H), 9.00 (s, 1H), 8.57 (d, J ¼ 9, 1H),
8.32 (d, J ¼ 9, 1H), 7.93 (d, J ¼ 9, 2H), 7.42 (d, J ¼ 9, 2H), 2.47 ꢀ
(s, 3H). 13C NMR: 188.91, 150.63, 143.37, 142.51, 136.64, 132.37,
129.53, 127.81, 120.90, 110.23, 107.51, 21.86 ꢀ. Anal. Calcd. for
C14H11N3O6S: C, 48.14; H, 3.17; N, 12.03. Found: C, 47.92; H, 2.81;
N, 12.27.
N-(1H-Indol-3-ylmethylene)-4-methyl-benzenesulfonamide (3o): Red
needles, m.p. 151ꢀC (dec). FTIR: 3352, 1633, 1571, 1524, 1441, 1301,
1
1239, 1156, 1099, and 907 cmÀ1. H NMR: 10.02 (s, 1H), 8.24 (d, J ¼ 9,
1H), 7.99 (d, J ¼ 9, 1H), 7.91 (d, J ¼ 9, 2H), 7.80 (d, J ¼ 9, 1H), 7.68–7.62
(m, 1H), 7.49–7.33 (m, 2H), 7.15 (d, 1H), 4.77 (bs, N-H), 2.44 ꢀ (s, 3H).
13C NMR: 243.35, 198.89, 185.11, 163.27, 135.05, 129.73 (overlapping
peak), 126.50 (overlapping peak), 124.46, 123.06, 111.43, 21.51 ꢀ. Anal.
Calcd. for C16H14N2O2S: C, 64.41; H, 4.73; N, 9.39. Found: C, 64.63;
H, 4.81; N, 10.11.
ACKNOWLEDGMENTS
Financial support by the Jeffress Trust is gratefully acknowledged
(Grant J-587). The authors also wish to thank Kristen Fitzgerald from
the GMU Biology Department for performing elemental analyses.

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Novel Functionalized N-Tosylaldimines
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Received in the USA February 22, 2002