The combination of TsNH2 and NCS as nitrogen and chlorine sources for direct diamination of enones

Article abstract of DOI:10.1002/ejoc.200300326

The regio-, stereo-, and chemoselective diamination of enones has been achieved without the observation of any haloamines. The reaction employs the readily available inexpensive combination of NCS and TsNH₂ as an electrophilic nitrogen source, and three nitriles as nucleophilic nitrogen sources. A novel mechanism involving the formation of aziridinium intermediates from the reaction of TsNHCl with olefins and a new [2+3] cyclic addition for aziridinim ring opening has been proposed for the electrophilic diamination of olefins. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.

Full text of DOI:10.1002/ejoc.200300326

FULL PAPER
The Combination of TsNH and NCS as Nitrogen and Chlorine Sources for
2
Direct Diamination of Enones
[a]
[a]
[a]
[a]
Cody Timmons, Dianjun Chen, Xin Xu, and Guigen Li*
Dedicated to Professor Henry Shine on the occasion of his 80th birthday
Keywords: Aminations / Olefins / Nitrogen heterocycles / Cycloadditions
The regio-, stereo-, and chemoselective diamination of en-
ones has been achieved without the observation of any
haloamines. The reaction employs the readily available inex-
dinium intermediates from the reaction of TsNHCl with ol-
efins and a new [2+3] cyclic addition for aziridinim ring open-
ing has been proposed for the electrophilic diamination of ol-
efins.
2
pensive combination of NCS and TsNH as an electrophilic
nitrogen source, and three nitriles as nucleophilic nitrogen
sources. A novel mechanism involving the formation of aziri-
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2003)
Introduction
ation product was formed. This new system has the advan-
tage that all starting materials are readily available, whereas
in the previous systems TsNCl had to be prepared indepen-
The development of new regio- and stereoselective routes
2
dently and used relatively quickly before it decomposed.
Thus, this new system is truly a very convenient and one-
pot diamination process. In this communication, we report
the preliminary results of this new system (Scheme 2 and
Table 1). Also, two previously unexplored nitriles, benzon-
itrile and isobutyronitrile, were successfully employed as nu-
cleophilic nitrogen sources and the resulting non-halogen-
ated products were obtained in promising yields (Table 2).
to vicinal diamine compounds has proven to be a challeng-
ing topic in organic synthesis.[1Ϫ5] These compounds are of
great importance owing to their many potential appli-
[
1,2]
cations in the medical and pharmaceutical fields.
To
date, the majority of the syntheses of these important com-
pounds centered around the use of transition metal pro-
[
6]
moters. Recent work in our lab has led to several methods
for the preparation of 1-p-tosyl-3-dichloromethyl-4,5-imida-
[
7,8]
[9]
zoline
and 1-p-tosyl-3-trichloromethyl-4,5-imidazoline
compounds. These can readily be hydrolyzed by 6  HCl to
yield the corresponding protected vicinal diamine products
Results and Discussion
(Scheme 1). In each case, N,N-dichloro-p-toluenesulfonam-
ide (TsNCl ) and MeCN were used as the electrophilic and
nucleophilic nitrogen sources, respectively (Scheme 1, con-
ditions A and B). We also discovered that α,β-unsaturated
2
The regio and stereochemistry resulting from this TsNH2/
NCS-based diamination with no metal catalyst suggests
that the previous mechanism hypothesis should be further
modified (Scheme 3). The first step of this reaction could
be the formation of N-monochloro-p-toluenesulfonamide
ketones react with TsNCl and MeCN in the absence of a
2
catalyst but with prolonged time to afford the dichlorinated
imidazoline derivatives in acceptable yields.[
8c]
(pTsNHCl) which reacts with olefin to form the N-(p-tosyl)-
Very recently, Sudalai and co-workers developed an ami-
nobromination methodology in which TsNH2 and NBS
served as the amine and bromine sources in the reaction
aziridinium intermediate A. To the best of our knowledge,
this is the first time that aziridinium intermediates have
been found to be generated by the reaction of TsNHCl with
alkenes. This step is similar to that of a previous diamin-
[
10]
with olefins.
Intrigued by their results, we sought to ex-
plore an analogous aminochlorination procedure in which
NCS replaced NBS. To our surprise, we found that when
MeCN was used as a solvent in the absence of any metal
catalyst, aminohalogenation did not occur but the diamin-
ation process where an N-chloroN-(p-tosyl)aziridinium
[11,12]
species was formed as the key intermediate.
The next
step, aziridinium ring opening, could proceed through a
2ϩ3] cyclic addition reaction between acetonitrile and N-
p-tosyl)aziridinium intermediate A to form 1-N-(p-tosyl)-
[
(
[
a]
Department of Chemistry and Biochemistry, Texas Tech
University,
Lubbock, TX 79409-1061, USA
E-mail: Guigen.Li@ttu.edu
imidazolinium B directly. This step controls both regio and
syn stereoselectivity. After intermediate B is deprotonated,
C is generated followed by chlorination by NCS to give rise
3850
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
DOI: 10.1002/ejoc.200300326
Eur. J. Org. Chem. 2003, 3850Ϫ3854

2
TsNH and NCS as Nitrogen and Chlorine Sources for Diamination of Enones
FULL PAPER
Scheme 1
Similar to our previous diamination and aminohalogen-
ation reactions, it was very convenient to carry out the pre-
sent diamination simply by mixing the reactants, olefin,
˚
TsNH , NCS, and 4-A molecular sieves in freshly distilled
2
acetonitrile. Since there are no sensitive catalysts involved,
the reaction can be performed without special protection
from inert gases. The capped reaction mixture was kept
stirred at 50 °C for the indicated period for each substrate
as shown in Tables 1 and 2 until completion was achieved,
as monitored by crude NMR analysis or TLC. Upon com-
pletion, the major side product, succinimide derived from
NCS, could be readily filtered off before further purification
of the diamine product.
Scheme 2
to D. Deprotonation of the 2-methyl group of D gives meth-
ylene scaffold E, which enables the second S 2Ј-type
displacement to afford 2-chloromethyl-4-phenyl-5-phenyl-
carbonyl-1-(p-tosyl)imidazoline (F), which is then converted
into the final imidazoline product through further similar
steps from C to F.
N
At the initial stage, chalcone was chosen as the substrate
for reaction optimization. It was found that at 50 °C stoi-
chiometric amounts of TsNH (one equivalent) and NCS
2
(two equivalents) afforded the product in limited yield (ca.
35Ϫ40%). Doubling the reactant quantities, i.e. two equiva-
lents of TsNH and four equivalents of NCS, increased the
2
yield to around 50%. However, at 50 °C a significant
amount of starting material remained even after three days.
It was found, however, that addition of a further two equiv-
alents of NCS after the reaction had proceeded for 24 h
solved this problem. Furthermore, although the reaction
did occur at room temperature, it proceeded very slowly.
Increasing the temperature to 50 °C allowed the reaction to
proceed to completion within three days. Table 1 illustrates
the diamination results using acetonitrile as the co-nitro-
gen source.
As can be seen from Table 1, terminal disubstituted ke-
tones reacted faster and gave higher yields. In no case did
cinnamate esters react to any appreciable extent, which is
different from previous systems. As far as chalcone deriva-
tives are concerned, all work well except for those with
strong electron-withdrawing substituents (e.g. 3- and 4-
nitrochalcone).
Scheme 3
˚
It should be noted that this aziridinium-based mecha-
The use of 4 A molecular sieves proved essential in that
nism can account for the regio- and stereoselectivity of the yields were reduced to almost one half when they were not
previous catalyzed aminochlorination processes.[11,12] In employed. The role of the molecular sieves during the reac-
those systems, the S 2 opening by chloride anion is respon- tion mechanism is not clear at this stage. One of their pos-
N
sible for the high anti stereoselectivity. The regioselectivity sible roles could be to absorb the hydrogen chloride which
is controlled by the fact that the β-position of the aziridin- is released during the reaction process.
ium intermediate has more positive charge than the α-posi-
After acetonitrile was successfully utilized for this direct
tion because of the stabilization effect from the phenyl ring. diamination, two other nitriles, benzonitrile (PhCN) and
Eur. J. Org. Chem. 2003, 3850Ϫ3854
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 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3851

C. Timmons, D. Chen, X. Xu, G. Li
FULL PAPER
Table 1. Results of TsNH2/NCS-based diamination of α,β-unsaturated ketones
[
a]
1
Estimated by crude H NMR determination. Ͼ 95% means no minor isomer was detected. No regio minor isomers were detected for
[
b]
1
Ϫ3. Yields after purification via column chromatography.
Table 2. Diamination using iPrCN and PhCN as the nitrogen sources
[
a]
The yields after purification via column chromatography.
isobutyronitrile (iPrCN) were also used as nucleophilic ni- vation can support the present ionic mechanism instead of
trogen sources (Table 2). When these two new nitrogen a radical one for the formation of carbonϪchlorine bonds
sources were used as solvents in lieu of MeCN, the resulting of the 2-methylene group of the final imidazoline product.
imidazoline adducts contained no chlorine atoms. This ob- Two substrates, phorone and mesityl oxide, were explored
servation indicates that S 2Ј-type displacement is inhibited with these alternative nitrogen sources. As summarized in
N
when using isobutyronitrile as the solvent. The steric effect Table 2, satisfactory yields were achieved in all these cases.
of the two methyl groups of this nitrogen source could be
The use of NBS to replace NCS as the halogen source
responsible for the inhibition. Importantly, the above obser- for this diamination reaction has not yet been successful. It
3852
 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Eur. J. Org. Chem. 2003, 3850Ϫ3854

2
TsNH and NCS as Nitrogen and Chlorine Sources for Diamination of Enones
FULL PAPER
seems more difficult to generate the aziridinium intermedi- (d, J ϭ 5.00 Hz, 1 H), 5.00 (d, J ϭ 5.00 Hz, 1 H), 2.46 (s, 3 H)
1
3
ppm. C NMR (125 MHz, CDCl
1
7
3
): δ ϭ 192.4, 156.7, 145.9, 141.0,
ate by the reaction between N-bromo-p-toluenesulfonamide
and electron-deficient olefins. A mechanism study by the
direct determination of various intermediates will be carried
out in our laboratories.
38.5, 134.3, 131.8, 132.0, 132.1, 129.4, 129.1, 128.8, 127.9, 126.5,
2.3, 72.0, 61.4, 21.7 ppm.
3
: Isolated as a white solid (336 mg, 67%). M.p. 119Ϫ121 °C. IR
(
deposit from CH
2
Cl
cm . H NMR (500 MHz, CDCl
(d, J ϭ 7.5 Hz, 3 H), 7.28Ϫ7.25 (m, 3 H), 7.21 (s, 1 H), 7.15Ϫ7.12
m, 2 H), 6.90Ϫ6.88 (m, 2 H), 5.50 (d, J ϭ 5 Hz, 1 H), 5.00 (d,
2
solution on a NaCl plate): ν˜ ϭ 1698(CϭO)
Ϫ1
1
3
): δ ϭ 7.80Ϫ7.77 (m, 3 H), 7.32
Conclusion
(
1
3
J ϭ 5 Hz, 1 H), 2.45 (s, 3 H) ppm. C NMR (125 MHz, CDCl
δ ϭ 191.9, 165.4, 156.7, 145.8, 138.6, 134.3, 131.6, 131.5, 130.1,
29.1, 127.9, 126.5, 116.4, 116.2, 73.3, 71.9, 61.4, 21.7 ppm.
3
):
A new method has been developed for the synthesis of
imidazoline derivatives using readily available inexpensive
1
starting materials, NCS and TsNH , under more convenient
2
conditions. This method eliminates the need to prepare and
4
: Isolated as a white solid (294 mg, 78% yield). M.p. 95Ϫ97 °C.
store the relatively unstable TsNCl . Benzonitrile and isobu- IR (deposit from CH Cl solution on NaCl plate): ν˜ ϭ 1715 (Cϭ
2
2
2
Ϫ1
1
tyronitrile were also successfully employed as nucleophilic O) cm . H NMR (500 MHz, CDCl ): δ ϭ 7.75 (d, J ϭ 8.46 Hz,
3
nitrogen sources to produce non-halogenated imidazoline 2 H), 7.41 (d, J ϭ 8.46 Hz, 2 H), 7.21 (s, 1 H), 3.99 (s, 1 H), 2.47
1
3
(
s, 3 H), 1.21 (s, 3 H), 0.89 (s, 3 H) ppm. C NMR (125 MHz,
CDCl ): δ ϭ 205.5, 153.5, 146.1, 133.2, 130.4, 127.6, 70.4, 61.7,
0.7, 27.8, 23.2, 21.7 ppm.
derivatives. This work demonstrates the first example of azi-
ridinium intermediate formation from the reaction of
TsNHCl with olefins.
3
3
5
: Isolated as a white solid (292 mg, 70% yield). M.p. 138Ϫ140 °C.
Cl
solution on NaCl plate): ν˜ ϭ 1685 (Cϭ
O) cm , H NMR (500 MHz, CDCl ): δ ϭ 7.78Ϫ7.74 (m, 2 H),
IR (deposit from CH
2
2
Ϫ1
1
Experimental Section
3
7.38Ϫ7.34 (m, 2 H), 7.21 (s, 1 H), 6.13 (s, 1 H), 4.10 (s, 1 H), 2.45
General Procedure: All reactions were conducted without inert gas
protection. Acetonitrile was dried and freshly distilled from calcium
hydride under a nitrogen atmosphere. All other chemicals were pur-
chased commercially and used without further purification, and
their stoichiometries were calculated based on the reported purities
from the manufacturers. Flash chromatography was performed on
(s, 3 H), 2.09 (d, J ϭ 1 Hz, 3 H), 1.88 (d, J ϭ 1 Hz, 3 H), 1.20 (s,
1
3
3 H), 1.01 (s, 3 H) ppm. C NMR (125 MHz, CDCl ): δ ϭ 195.1,
3
160.6, 153.4, 145.6, 133.9, 130.1, 127.8, 120.1, 76.7, 70.5, 62.0, 30.7,
28.2, 23.4, 21.7, 21.2 ppm.
6: Isolated as a colorless oil (237 mg, 74% yield). HRMS: MHϩ:
1
374.1419, calculated: 374.1424. IR (deposit from CH Cl solution
silica gel 60 (230Ϫ400 mesh). H NMR spectroscopy (500 MHz)
2
2
Ϫ1
1
and 1 C NMR spectroscopy (125 MHz) were acquired in deuter-
3
on NaCl plate): ν˜ ϭ 1716 (CϭO) cm
CDCl ): δ ϭ 7.69Ϫ7.66 (m, 2 H), 7.54Ϫ7.50 (m, 1 H), 7.44Ϫ7.41
m, 4 H), 7.27Ϫ7.28 (m, 2 H), 4.22 (s, 1 H), 2.43 (s, 3 H), 2.42 (s,
. H NMR (500 MHz,
ated chloroform (CDCl ). High-resolution mass spectral analysis
3
3
(
3
was conducted by the mass spectrometry laboratory of the Scripps
Research Institute. Melting points are reported uncorrected. Prod-
ucts 1, 2, 4, and 5 can be identified based on comparison to
known compounds.
1
3
H), 1.22 (s, 3 H), 0.91 (s, 3 H) ppm. C NMR (125 MHz,
): δ ϭ 206.3, 156.0, 145.1, 134.0, 131.1, 129.8, 129.6, 127.8,
27.8, 76.6, 69.9, 31.2, 28.3, 24.3, 21.6 ppm.
CDCl
1
3
˚
7: Isolated as a colorless oil (212 mg, 63% yield). HRMS: MHϩ:
General Procedure for Direct Diamination: Olefin (1.0 mmol), 4-A
molecular sieves (0.50 g), TsNH (342 mg, 2 mmol), NCS (534 mg,
mmol), and freshly distilled acetonitrile (6 mL) were added to a
dry vial. The vial was capped and the contents stirred at 50 °C for
4 h, when an additional portion of NCS (267 mg, 2 mmol) was
introduced. Stirring was continued at 50 °C until the reaction was
complete, as monitored by crude NMR analysis or TLC, when the
solid residue was filtered off and washed with EtOAc (3 ϫ 15 mL).
The resulting solution was condensed under reduced pressure and
purified via flash chromatography (EtOAc/hexane, 1:4) to afford
the pure product.
3
37.1579, calculated: 337.158. IR (deposit from CH
2
Cl
2
solution
2
Ϫ1
1
on NaCl plate): ν˜ ϭ 1716 (CϭO) cm
. H NMR (500 MHz,
3
): δ ϭ 7.74Ϫ7.71 (m, 2 H), 7.37 (d, J ϭ 8 Hz, 2 H), 3.99 (s,
4
CDCl
H), 3.33 (septet, J ϭ 7 Hz, 1 H), 2.45 (s, 3 H), 2.27 (s, 3 H), 1.33
d, J ϭ 6.5 Hz, 3 H), 1.20 (d, J ϭ 6.5 Hz, 3 H), 1.11 (s, 3 H), 0.88
1
2
(
(
1
3
s, 3 H) ppm. C NMR (125 MHz, CDCl
3
): δ ϭ 206.5, 161.8,
1
2
45.0, 134.8, 130.1, 127.3, 76.1, 68.8, 31.5, 28.4, 28.0, 24.0, 22.2,
1.6, 19.8 ppm.
8
CH
: Isolated as a colorless oil (250 mg, 61% yield). IR (deposit from
Ϫ1
1
Cl
2
solution on NaCl plate): ν˜ ϭ 1685 (CϭO) cm . H NMR
2
1
: Isolated as a white solid (299 mg, 61% yield). M.p. 130Ϫ131 °C.
IR (deposit from CH Cl
solution on a NaCl plate): ν˜ ϭ 1698 (Cϭ
O) cm . H NMR (300 MHz, CDCl
(500 MHz, CDCl ): δ ϭ 7.66Ϫ7.64 (m, 2 H), 7.51Ϫ7.48 (m, 1 H),
7.44Ϫ7.38 (m, 4 H), 7.26Ϫ7.24 (m, 2 H), 6.37 (s, 1 H), 4.31 (s, 1
3
2
2
Ϫ1
1
): δ ϭ 7.80Ϫ7.74 (m, 4 H), H), 2.42 (s, 3 H), 2.24 (s, 3 H), 2.00 (s, 3 H), 1.21 (s, 3 H), 0.98 (s,
3
1
3
7
.64Ϫ7.61 (m, 1 H), 7.49Ϫ7.44 (m, 2 H), 7.32Ϫ7.23 (m, 6 H), 6.90 3 H) ppm. C NMR (125 MHz, CDCl
3
): δ ϭ 196.0, 159.8, 156.0,
(
dd, J ϭ 1.40, 8.02 Hz, 2 H), 5.56 (d, J ϭ 4.86 Hz, 1 H), 5.01 (d, 144.8, 134.7, 130.9, 129.6, 129.5, 127.9, 127.8, 120.9, 76.5, 69.9,
13
J ϭ 4.86 Hz, 1 H), 2.45 (s, 3 H) ppm. C NMR (75 MHz, CDCl
δ ϭ 193.3, 156.7, 145.7, 138.7, 134.4, 134.3, 133.5, 130.1, 129.0(2),
3
): 31.2, 28.3, 24.4, 21.6, 21.3 ppm.
9: Isolated as a colorless oil (278 mg, 74% yield). IR (deposit from
128.8, 128.7, 126.6, 72.3, 71.9, 61.4, 21.7 ppm.
Ϫ1
1
CH
2
Cl
2
solution on NaCl plate): ν˜ ϭ 1683 (CϭO) cm . H NMR
2: Isolated as a white solid (326 mg, 62% yield). M.p. 96Ϫ98 °C.
(500 MHz, CDCl ): δ ϭ 7.70Ϫ7.75 (m, 2 H), 7.36Ϫ7.34 (m, 2 H),
3
IR (deposit from CH
O) cm . H NMR (500 MHz, CDCl
2
Cl
2
solution on a NaCl plate): ν˜ ϭ 1869 (Cϭ
): δ ϭ 7.77 (d, J ϭ 8.5 Hz,
6.17 (s, 1 H), 4.10 (s, 1 H), 3.29 (septet, J ϭ 7 Hz, 1 H), 2.44 (s, 3
H), 2.18 (d, J ϭ 1 Hz, 3 H), 1.94 (d, J ϭ 1 Hz, 3 H), 1.29 (d, J ϭ
Ϫ1
1
3
2
7
H), 7.69 (d, J ϭ 8.5 Hz, 2 H), 7.44 (d, J ϭ 8.99 Hz, 2 H), 7 Hz, 3 H), 1.20 (d, J ϭ 7 Hz, 3 H), 1.10 (s, 3 H), 0.95 (s, 3 H)
1
3
.33Ϫ7.26 (m, 5 H), 7.21 (s, 1 H), 6.89 (d, J ϭ 8.50 Hz, 2 H), 5.48
ppm. C NMR (125 MHz, CDCl
3
): δ ϭ 196.3, 161.8, 159.1, 144.7,
Eur. J. Org. Chem. 2003, 3850Ϫ3854
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 2003 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 3853

C. Timmons, D. Chen, X. Xu, G. Li
FULL PAPER
[
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We gratefully acknowledge financial support from the Robert A.
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Texas Excellence Fund Fellowships for D. Chen and C. Timmons.
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Eur. J. Org. Chem. 2003, 3850Ϫ3854