Phosphane-catalyzed [3+2] cycloaddition reaction of allenoate and cyclic imines: A simple and efficient method for synthesis of benzo-fused cyclic sulfamidate heterocycles

Article abstract of DOI:10.1002/ejoc.201201756

By using a phosphane as an organocatalyst, an efficient synthesis of benzo-fused cyclic sulfamidate heterocycles has been developed through a cycloaddition reaction of allenoate and cyclic imines including cyclic trifluoromethyl ketimine, which gave high yields (71-97 %). The reaction could also be conveniently performed on a gram scale. Furthermore, some simple transformations of the sulfamidate heterocycle products have been disclosed to obtain functional amines. An asymmetric variant of this reaction was also tried by screening several commercially available chiral phosphane ligands as organocatalysts, and up to 36 % ee was achieved. Benzo-fused cyclic sulfamidate heterocycles have been synthesized in 71-97 % yields through a cycloaddition reaction of allenoate with cyclic imines (various aldimines and a trifluoromethyl ketimine) by using PPh₃ as organocatalyst. After screening several commercially available chiral phosphanes, up to 36 % ee was obtained with (R)-H₈-BINAP. Copyright

Full text of DOI:10.1002/ejoc.201201756

FULL PAPER
DOI: 10.1002/ejoc.201201756
Phosphane-Catalyzed [3+2] Cycloaddition Reaction of Allenoate and Cyclic
Imines: A Simple and Efficient Method for Synthesis of Benzo-Fused Cyclic
Sulfamidate Heterocycles
You-Qing Wang,*[a] Yongna Zhang,[b] Haina Dong,[a] Jie Zhang,[a] and Jin Zhao[a]
Keywords: Allenes / Cyclic sulfamidates / Cycloaddition / Organocatalysis / Phosphanes / Heterocycles
By using a phosphane as an organocatalyst, an efficient syn-
thesis of benzo-fused cyclic sulfamidate heterocycles has
been developed through a cycloaddition reaction of allenoate
and cyclic imines including cyclic trifluoromethyl ketimine,
which gave high yields (71–97%). The reaction could also be
conveniently performed on a gram scale. Furthermore, some
simple transformations of the sulfamidate heterocycle prod-
ucts have been disclosed to obtain functional amines. An
asymmetric variant of this reaction was also tried by screen-
ing several commercially available chiral phosphane ligands
as organocatalysts, and up to 36% ee was achieved.
cently, cyclic sulfamidates were synthesized through enan-
tioselective Rh-catalyzed addition reactions of organic
boron reagents to cyclic imines as reported by Lam[7a,7b]
and one example by Nishimura and co-workers.[7c] Despite
the impressive progress achieved, the use of a catalytic ap-
proach to cyclic sulfamidate heterocycles is still underex-
plored. These reactions are limited to the use of transition-
metal catalysts, and at this time there are no descriptions
of organocatalytic processes to generate cyclic sulfamidate
heterocycles. Notably, benzo-fused sulfamidate heterocycles
have received little attention.[3d,4e,5a,6,7] Therefore, it will be
of interest to develop new and efficient organocatalytic
methods for the synthesis of cyclic sulfamidate heterocycles
(Scheme 1).
Introduction
Cyclic sulfamidate heterocycles, 1,2,3-oxathiazolidine
2,2-dioxides,[1] play important roles in the synthesis of a
wide variety of chemically and biologically important alk-
ylamines, because they can undergo nucleophilic displace-
ment with a carbon anion or other heteroatom nucleo-
phile.[1,2] Such heterocycles have generally been synthesized
by oxidation of their corresponding sulfamidites that could
be assembled from amino alcohols or diols.[1] The use of
synthetic methodologies, especially in the presence of cata-
lysts, is particularly attractive when considering the econ-
omy and efficiency of a process. The Du Bois group initially
reported the intramolecular amination of the saturated C–
H bonds of sulfamate esters to afford cyclic sulfamidates by
using dinuclear Rh catalysis.[3] Subsequently, the intramo-
lecular amination of sulfamates esters was developed to ef-
ficiently and stereoselectively provide a series of cyclic sulf-
amidates catalyzed by Rh, Ru, Mn, Cu, Ag, and Au com-
plexes.[4] The Pd-catalyzed asymmetric hydrogenation and
Rh-catalyzed asymmetric transfer hydrogenation of cyclic
sulfamidates have also been reported to result in cyclic sulf-
amidates.[5] A one-pot highly diastereoselective synthesis of
cyclic sulfamidates containing a quaternary carbon center
was realized by the combination of a sulfur-ylide-mediated
aziridination and Pd0-catalyzed isomerization.[6] Very re-
Scheme 1. Catalytic approach for the synthesis of cyclic sulfamidate
heterocycles.
[a] Key Laboratory of Natural Medicine and Immuno-Engineering
of Henan Province, Henan University,
Kaifeng, Henan 475004, People’s Republic of China
Fax: +86-378-2864665
Phosphane-catalyzed [3+2] cycloaddition reactions of
electron-deficient allenes or alkynes and imines, also known
as the Lu reaction,[8] is a privileged method in organic syn-
thesis and has attracted much attention.[9,10] This reaction
allows the formation of new five-membered polyfunction-
alized nitrogen heterocycles that may be valuable synthons
E-mail: wyouqing@hotmail.com
wyouqing@foxmail.com
[b] Basic Experiment Teaching Center, Henan University,
Kaifeng, Henan 475004, People’s Republic of China
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201201756.
3764
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Synthesis of Benzo-Fused Cyclic Sulfamidate Heterocycles
for fine chemistry. The imines used for this reaction are Table 1. Optimizaion of reaction conditions for the Ph3P-catalyzed
[3+2] cycloaddition reaction of allenoate 2a and cyclic imine 1a.
acyclic N-Ts- and N-(diphenyphosphinoyl)amide imines.
Very recently, Ye et al. reported the phosphane-catalyzed
[3+2] cycloaddition reaction of five-membered cyclic
sulfonamide ketimines to give sultam-fused dihydropyr-
roles[10k] and used the same cyclic imines as electrophiles
in [4+2] cycloaddition reactions catalyzed by phophanes to
afford the corresponding tetrahydropyridines.[11] Here, we
wish to report the synthesis of benzo-fused 1,2,3-benz-
oxathiazine 2,2-dioxide heterocycles through phosphane-
catalyzed [3+2] cycloaddition reactions of allenoate (α-
allenic ester) and cyclic imines 1.
Entry[a] Catalyst Solvent Concentration[b]
T
[°C]
Time Yield
[h]
[%][c]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16[d]
17[e]
18[f]
Ph3P
Ph3P
Ph3P
Ph3P
Ph3P
Ph3P
Ph3P
Ph3P
Ph3P
toluene
CH2Cl2
THF
MeOH
CH3CN
DMF
toluene
toluene
toluene
0.1 m
0.1 m
0.1 m
0.1 m
0.1 m
0.1 m
0.1 m
0.1 m
0.1 m
0.1 m
0.1 m
0.1 m
0.1 m
0.2 m
0.5 m
0.2 m
0.2 m
0.2 m
12
12
12
12
12
12
25
25
50
25
25
25
25
25
25
25
25
25
6
6
6
99
61
trace
13
6
6
6
2.5
4.5
1
39
trace
96
92
89
Results and Discussion
In our initial experiment, the reaction of cyclic imine 1a
and benzyl allenoate (2a) was carried out at 12 °C with
Ph3P (10 mol-%) as a catalyst in toluene. Full conversion
could be observed as shown by TLC, and α-addition re-
gioselective product 3a was isolated in a quantitative yield
(Table 1, Entry 1). The structure of the isolated product was
characterized by 1H and 13C NMR spectroscopy as well
as HRMS. The different product structures, such as [2+2]
cycloadducts or Morita–Baylis–Hillman products, are
possibly obtained from the reaction of allenoates and a
C=N group, whereas only the N-substituent of the imines
or catalysts were changed.[12] Therefore, it was necessary to
clearly confirm the structure of compound 3a by single-
crystal X-ray diffraction analysis (Figure 1).[13] The analysis
showed that an α-regioselective isomer of the [3+2] cycload-
duct was obtained.
Ph2PMe toluene
5
64
72
0
35
93
92
93
Bu3P
DBU
DBU
Ph3P
Ph3P
Ph3P
Ph3P
Ph3P
toluene
toluene
CH2Cl2
toluene
toluene
toluene
toluene
toluene
16
72
24
2.5
1.5
6
72
72
87
39
[a] General reaction conditions: 0.05 mmol scale: Ratio 1a/2a =
1:1.5 for Entries 1–7, and 1:1.2 for Entries 8–18. [b] Concentration
of imine 1a in toluene. [c] Isolated yield. [d] Ph3P (5 mol-%).
[e] Ph3P (2 mol-%). [f] Ph3P (1 mol-%).
Next we investigated the influence of different factors re-
lated to reactivity as listed in Table 1. Firstly, solvent effects
were studied. We stopped the reaction at the same time to
evaluate the reactivity, and only toluene, as the best solvent,
provided full conversion after 6 h (Table 1, Entries 1–6).
The ratio of 1a/2a also affected the reactivity (Table 1, En-
tries 7 and 8), and a slight excess of 2a (1.2 equiv.) was cho-
sen. Next, temperature increases were shown to consider-
ably accelerate the rate of the reaction (Table 1, Entries 1
versus 7, and 8 versus 9), which is usually observed with
chemical reactivity. Interestingly, the same product was ob-
served by using other phosphane and amine catalysts
(Table 1, Entries 10–13). However, a few by-products were
Figure 1. Single-crystal X-ray structure of 3a.
1
seen by TLC and crude H NMR analysis. When the con-
centration of imine 1a was increased from 0.1 m to 0.2 m or 5 mol-% of Ph3P is optimal to ensure high reaction effi-
more, the reaction activity improved significantly (Table 1, ciency (93% yield) and maintain a reasonable reaction time
Entries 8 and 14–15). Considering the solubility of 1a in (Table 1, Entry 16).
toluene at a concentration of 0.5 m, we selected the optimal
Under the optimized conditions, the reactions of allen-
concentration of 1a in toluene to be 0.2 m. The studies of oate 2a and various cyclic imines 1, which may be conve-
catalyst loadings on the reaction revealed that the reaction niently obtained from salicylaldehydes and chlorosulfonyl
rate decreased as the catalyst loading was reduced. With isocyanate in one step,[14] were conducted in the presence
2 mol-% of phosphane catalyst the reaction was still effec- of Ph3P in dry toluene at room temperature without any
tive, although more time was required to complete the reac- special handling. As shown in Scheme 2, the benzo-fused
tion. However, a further decrease in the catalyst loading to cyclic sulfamidate heterocycles 3, with a variety of substitu-
1 mol-% rendered the reaction unacceptably slow (Table 1, ents at different positions on the aromatic ring, can be read-
Entries 16–18). From an operational perspective, the use of ily obtained in high isolated yields. For methoxy-substituted
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Y.-Q. Wang, Y. Zhang, H. Dong, J. Zhang, J. Zhao
FULL PAPER
Scheme 2. Cycloaddition reaction with various substrates 1.
imine 1g, a slightly lower yield was obtained. Interestingly,
cycloadduct 1i containing a tertiary amine group, which can
act as a Lewis base owing to its nucleophilicity, was also
obtained in 94% yield. Imines with two substituents leading
to steric hindrance were also used and gave corresponding
cyclic sulfamidate heterocycles 3j, 3k, and 3l in high isolated
yields.
Scheme 4. Gram-scale experiment.
Fluorine plays a key role in pharmaceutical, veterinary,
agrochemical, and material sciences, and α-(trifluorometh-
yl)-substituted amines are essential structural motifs in a
large number of pharmaceutical, agrochemical, and organic
materials.[15] Consequently, there have been reports of pre-
paring α-(trifluoromethyl)-substituted amines by means of
a few catalytic addition reactions to cyclic trifluoromethyl
ketimine.[16] We were attracted to the possibility of a Ph3P-
catalyzed cycloaddition reaction of allenoate 2 and cyclic
trifluoromethyl ketimine 4. It was found that the reaction
proceeded smoothly to give α-(trifluoromethyl) quaternary
carbon amine 5 in 76% yield at 50 °C, although no reaction
occurred at room temperature (Scheme 3).
Benzo-fused cyclic sulfamidate heterocycles 3 are attract-
ive synthetic intermediates as multifunctional compounds.
Typical transformations for cyclic sulfamidates 3a were car-
ried out, and the results are illustrated in Scheme 5. When
a mixture of cycloadduct 3a and 2,3-dichloro-5,6-dicyano-
benzoquinone (DDQ) in benzene was heated to 120 °C for
1.5 d in a sealed tube, aromatization occurred smoothly,
and a pyrrole derivative was obtained in 90% yield. With
LiAlH4 as the nucleophilic reagent, 3a could be converted
into aminophenol 7, which is an important building block
and useful structural unit in organic synthesis.
Scheme 3. Cycloaddition reaction with cyclic trifluoromethyl ket-
imine 4.
To test the practicality of the current method, the cyclo-
addition reaction on a gram scale (1.191 g, 6.50 mmol of
1a) was carried out in toluene at room temperature to give
cyclic sulfamidates 3a in 92% yield (Scheme 4).
Scheme 5. Transformations of product 3a.
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Synthesis of Benzo-Fused Cyclic Sulfamidate Heterocycles
Some commercially available chiral phosphane ligands sterically hindered group in the presence of (R)-SYNPHOS
were screened for the reaction of 1a with 2. The results are (Table 2, Entries 10 and 11).
listed in Table 2. (R)-SYNPHOS delivered the best result
Based on the widely accepted proposed mechanism for
(66% yield, 27% ee). (R)-H8-BINAP delivered the best nucleophilic phosphane catalysis[9] and the experimental re-
enantioselectivity (36% ee) but with lower reactivity (24% sults from our current studies, a possible catalytic cycle for
yield). However, the reactivity decreased when ethyl allen- the above [3+2] annulation reactions is depicted in
oate (2b) was used instead of benzyl allenoate (2a), and no Scheme 6. The nucleophilic Ph3P initially attacks the β-car-
reaction was observed for tert-butyl allenoate (2c) with a bon atom of benzyl allenoate (2a) to yield allylic zwitterion
A. Subsequently, the α-carbon atom of anionic allylic A
may add to the C=N group of cyclic imine 1, and then
intramolecular Michael addition reaction of B affords cy-
cloadduct C. The proton shift of intermediate C brings
Table 2. Screening of commercial chiral phosphane ligands as or-
ganocatalysts.
about final zwitterionic intermediate D, which dissociates
to give product 3 and regenerates the Ph3P catalyst.
Conclusions
We have developed a high-yielding method for the syn-
thesis of benzo-fused cyclic sulfamidate heterocycles
through the [3+2] cycloaddition reaction of allenoate and
cyclic imines catalyzed by Ph3P. This represents the first
demonstration of an organocatalytic reaction to synthesize
cyclic sulfamidate heterocycles, which are easily attacked by
many nucleophiles to obtain functionalized amines. Further
extensions of the utility of these new benzo-fused cyclic
sulfamidate heterocycles, as well as the development of a
highly enantioselective synthesis of nitrogen heterocycles,
are underway in our laboratory.
Experimental Section
General: 1H and 13C NMR spectra were recorded with Bruker
1
DRX-400 spectrometers. The chemical shifts for H NMR spectra
were recorded relative to tetramethylsilane (TMS) with the solvent
[a] General reaction conditions: 0.05 mmol scale, chiral phosphane
(10 mol-%). [b] (R)-SYNPHOS (20 mol-%) was used. [c] Product
3m in 89% yield was obtained with Ph3P (5 mol-%) in toluene at
room temperature for12 h.
resonance employed as the internal standard (CDCl3:
δ =
7.26 ppm). The chemical shifts for 13C NMR spectra were recorded
relative to the central peak of deuteriochloroform (δ =77.0 ppm) as
the internal standard. Flash column chromatography was per-
formed with silica gel (200–300 mesh). TLC analysis was performed
on glass-backed plates coated with 0.2 mm silica. After elution, the
plate was visualized under 254 nm UV illumination, and further
visualization was achieved by staining with basic KMnO4 solution.
All commercially available compounds were used as provided with-
out further purification. All solvents used in the reactions were
distilled from appropriate drying agents prior to use, unless other-
wise noted. Cyclic imines 1a–l and 4 were prepared from the corre-
sponding salicylaldehydes according to modified procedures re-
ported in the literature.[14b] Benzyl allenoate (2a) was prepared ac-
cording to a literature procedure.[17]
General Procedure for the [3+2] Cycloaddition Reaction of Cyclic
Imines 1 Catalyzed by Ph3P: Table 1 and Scheme 2. To allenoate
2a (0.12 mmol) in anhydrous toluene (0.5 mL) was added cyclic
imine 1 and triphenylphosphane (5 mol-%). The mixture was
stirred at room temperature until the imine was shown to have re-
acted as monitored by TLC. The crude reaction mixture was di-
rectly charged on silica gel and purified by column chromatography
(petroleum ether/ethyl acetate) to afford the desired product.
Benzyl
3,10b-Dihydrobenzo[e]pyrrolo[1,2-c][1,2,3]oxathiazine-1-
Scheme 6. Proposed catalytic cycle.
carboxylate 5,5-Dioxide (3a): Rf = 0.3 (petroleum ether/ethyl acet-
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Y.-Q. Wang, Y. Zhang, H. Dong, J. Zhang, J. Zhao
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1
ate, 5:1). H NMR (400 MHz, CDCl3): δ = 7.59 (d, J = 10.4 Hz, 1 129.40, 129.35, 129.1, 128.8, 113.4, 113.1, 104.7, 67.9, 67.0, 56.6,
H), 7.39–7.26 (m, 6 H), 7.10 (dt, J = 1.4, 10.3 Hz, 1 H), 7.02 (dd,
J = 1.3, 11.0 Hz, 1 H), 6.89 (s, 1 H), 6.15 (d, J = 4.4 Hz, 1 H), 5.31
(AB q, ΔδAB = 0.09 ppm, JAB = 16.2 Hz, 2 H), 4.49–4.35 (m, 2 H)
ppm. 13C NMR (100 MHz, CDCl3): δ = 162.1, 149.8, 137.9, 135.2,
135.0, 129.5, 128.71, 128.68, 128.4, 127.3, 126.0, 120.7, 119.2, 67.3,
66.6, 55.9 ppm. HRMS (ESI): calcd. for C18H16NO5S [M + H]+
358.0744; found 358.0740.
56.2 ppm. HRMS (ESI): calcd. for C19H18NO6S [M + H]+
388.0849; found 388.0851.
Benzyl 7-Methoxy-3,10b-dihydrobenzo[e]pyrrolo[1,2-c][1,2,3]oxathi-
azine-1-carboxylate 5,5-Dioxide (3h): Rf = 0.30 (petroleum ether/
ethyl acetate, 5:1). 1H NMR (400 MHz, CDCl3): δ = 7.39–7.36 (m,
5 H), 7.13 (d, J = 7.9 Hz, 1 H), 7.02 (t, J = 8.1 Hz, 1 H), 6.88–6.86
(m, 2 H), 6.14 (d, J = 4.1 Hz, 1 H), 5.30 (AB q, ΔδAB = 0.08 ppm,
JAB = 12.2 Hz, 2 H), 4.49–4.36 (m, 2 H), 3.87 (s, 3 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 162.1, 149.0, 139.5, 137.9, 135.2,
135.0, 128.70, 128.65, 128.4, 125.6, 121.6, 118.2, 111.9, 67.2, 66.7,
56.2, 56.0 ppm. HRMS (EI): calcd. for C19H17O6NS [M]+
387.0777; found 387.0774.
Benzyl
9-Fluoro-3,10b-dihydrobenzo[e]pyrrolo[1,2-c][1,2,3]oxathi-
azine-1-carboxylate 5,5-Dioxide (3b): Rf = 0.32 (petroleum ether/
ethyl acetate, 5:1). 1H NMR (400 MHz, CDCl3): δ = 7.44–7.40 (m,
6 H), 7.01–6.99 (m, 2 H), 6.92 (s, 1 H), 6.09 (s, 1 H), 5.32 (AB q,
ΔδAB = 0.07 ppm, JAB = 12.2 Hz, 2 H), 4.42 (m, 2 H) ppm. 13C
1
NMR (100 MHz, CDCl3): δ = 162.0, 159.5 (d, JC-F = 244.5 Hz),
Benzyl 9-(Diethylamino)-3,10b-dihydrobenzo[e]pyrrolo[1,2-c][1,2,3]-
oxathiazine-1-carboxylate 5,5-Dioxide (3i): Rf = 0.50 (petroleum
ether/ethyl acetate, 5:1). 1H NMR (400 MHz, CDCl3): δ = 7.40–
7.33 (m, 6 H), 6.82 (s, 1 H), 6.39 (dd, J = 2.6, 8.9 Hz, 1 H), 6.22
(d, J = 2.6 Hz, 1 H), 6.03 (d, J = 3.9 Hz, 1 H), 5.30 (AB q, ΔδAB
= 0.08 ppm, JAB = 12.2 Hz, 2 H), 4.41–4.33 (m, 2 H), 3.30 (q, J =
7.1 Hz, 4 H), 1.14 (t, J = 7.1 Hz, 6 H) ppm. 13C NMR (100 MHz,
CDCl3): δ = 162.3, 150.9, 148.4, 137.0, 135.9, 135.1, 128.7, 128.5,
128.3, 127.8, 109.3, 106.0, 100.6, 67.0, 66.3, 55.9, 44.3, 12.4 ppm.
HRMS (ESI): calcd. for C22H24N2O5NaS [M + Na]+ 451.1304;
found 451.1307.
4
145.7 (d, JC-F = 2.8 Hz), 138.4, 134.8, 134.7, 128.8, 128.5, 122.2
3
3
2
(d, JC-F = 7.5 Hz), 120.8 (d, JC-F = 8.3 Hz), 116.5 (d, JC-F
=
=
2
4
23.8 Hz), 114.2 (d, JC-F = 25.8 Hz), 109.9, 67.5, 66.5 (d, JC-F
2.6 Hz), 56.0 ppm. HRMS (ESI): calcd. for C18H14FNNaO5S [M
+ Na]+ 398.0469; found 398.0472.
Benzyl 9-Chloro-3,10b-dihydrobenzo[e]pyrrolo[1,2-c][1,2,3]oxathi-
azine-1-carboxylate 5,5-Dioxide (3c): Rf = 0.26 (petroleum ether/
1
ethyl acetate, 5:1). H NMR (400 MHz, CDCl3): δ = 7.68 (s, 1 H),
7.40–7.38 (m, 5 H), 7.26–7.24 (m, 1 H), 6.98–6.92 (m, 2 H), 6.09
(s, 1 H), 5.32 (AB q, ΔδAB = 0.05 ppm, JAB = 9.9 Hz, 2 H), 4.46–
4.37 (m, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 162.2, 148.6,
138.6, 135.0, 134.9, 131.4, 129.8, 129.01, 129.00, 128.8, 127.6,
122.4, 120.8, 67.8, 66.6, 56.2 ppm. HRMS (ESI): calcd. for
C18H18ClN2O5S [M + NH4]+ 409.0620; found 409.0615.
Benzyl 7,9-Dibromo-3,10b-dihydrobenzo[e]pyrrolo[1,2-c][1,2,3]oxa-
thiazine-1-carboxylate 5,5-Dioxide (3j): Rf = 0.29 (petroleum ether/
1
ethyl acetate, 5:1). H NMR (400 MHz, CDCl3): δ = 7.83 (s, 1 H),
7.68 (s, 1 H), 7.40 (s, 5 H), 6.94 (s, 1 H), 6.10 (s, 1 H), 5.35–5.29
(m, 2 H), 4.50–4.39 (m, 2 H) ppm. 13C NMR (100 MHz, CDCl3):
δ = 161.8, 146.0, 138.6, 135.7, 134.7, 134.4, 129.4, 128.8, 128.6,
124.0, 118.6, 113.9, 67.6, 66.5, 56.2 ppm. HRMS (EI): calcd. for
C18H13O5NBr2S [M]+ 512.8881; found 512.8886.
Benzyl
9-Bromo-3,10b-dihydrobenzo[e]pyrrolo[1,2-c][1,2,3]oxathi-
azine-1-carboxylate 5,5-Dioxide (3d): Rf = 0.24 (petroleum ether/
1
ethyl acetate, 5:1). H NMR (400 MHz, CDCl3): δ = 7.83 (s, 1 H),
7.41 (s, 6 H), 6.93–6.91 (m, 2 H), 6.10 (s, 1 H), 5.36–5.29 (m, 2 H),
4.42 (s, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 161.9, 148.9,
138.4, 134.8, 134.7, 132.6, 130.3, 128.82, 128.79, 128.60, 122.6,
120.9, 118.7, 67.6, 66.3, 56.0 ppm. HRMS (ESI): calcd. for
C18H18BrN2O5S [M + NH4]+ 453.0114; found 453.0108.
Benzyl 7-Bromo-9-chloro-3,10b-dihydrobenzo[e]pyrrolo[1,2-c][1,2,3]-
oxathiazine-1- carboxylate 5,5-Dioxide (3k): Rf = 0.32 (petroleum
1
ether/ethyl acetate, 5:1). H NMR (400 MHz, CDCl3): δ = 7.69 (s,
1 H), 7.54 (s, 1 H), 7.40 (s, 5 H), 6.94 (s, 1 H), 6.09 (s, 1 H), 5.32
(AB q, ΔδAB = 0.05 ppm, JAB = 12.1 Hz, 2 H), 4.39–4.50 (m, 2 H)
ppm. 13C NMR (100 MHz, CDCl3): δ = 161.8, 145.5, 138.6, 134.7,
134.4, 132.9, 131.3, 128.8, 128.6, 126.5, 123.6, 113.6, 67.6, 66.6,
56.2 ppm. HRMS (EI): calcd. for C18H13O5NBrClS [M]+ 468.9386;
found 468.9390.
Benzyl 9-Methyl-3,10b-dihydrobenzo[e]pyrrolo[1,2-c][1,2,3]oxathi-
azine-1-carboxylate 5,5-Dioxide (3e): Rf = 0.32 (petroleum ether/
ethyl acetate, 5:1). 1H NMR (400 MHz, CDCl3): δ = 7.41–7.35 (m,
6 H), 7.07 (d, J = 8.3 Hz, 1 H), 6.92–6.89 (m, 2 H), 6.10 (s, 1 H),
5.33 (AB q, ΔδAB = 0.08 ppm, JAB = 12.2 Hz, 2 H), 4.45–4.36 (m,
2 H), 2.19 (s, 3 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 162.2,
147.7, 137.9, 135.8, 135.3, 135.1, 130.1, 128.74, 128.71, 128.5,
127.4, 120.2, 118.9, 67.2, 66.6, 55.9, 20.8 ppm. HRMS (ESI): calcd.
for C19H17NNaO5S [M + Na]+ 394.0720; found 394.0713.
Benzyl 7,9-Di-tert-butyl-3,10b-dihydrobenzo[e]pyrrolo[1,2-c][1,2,3]-
oxathiazine-1-carboxylate 5,5-Dioxide (3l): Rf = 0.30 (petroleum
ether/ethyl acetate, 10:1), identical to imine 1l. 1H NMR (400 MHz,
CDCl3): δ = 7.56 (d, J = 1.8 Hz, 1 H), 7.38–7.33 (m, 5 H), 7.31 (d,
J = 2.2 Hz, 1 H), 6.87 (s, 1 H), 6.15 (d, J = 4.2 Hz, 1 H), 5.29 (AB
q, ΔδAB = 0.14 ppm, JAB = 12.2 Hz, 2 H), 4.51–4.37 (m, 2 H), 1.41
(s, 9 H), 1.22 (s, 9 H) ppm. 13C NMR (100 MHz, CDCl3): δ =
162.3, 148.0, 146.7, 139.4, 137.7, 135.6, 135.1, 128.7, 128.6, 128.5,
124.1, 122.1, 120.3, 67.2, 67.1, 56.3, 35.1, 34.7, 31.2, 30.0 ppm.
HRMS (ESI): calcd. for C26H31NO5NaS [M + Na]+ 492.1821;
found 492.1828.
Benzyl 9-Methoxyl-3,10b-dihydrobenzo[e]pyrrolo[1,2-c][1,2,3]oxathi-
azine-1-carboxylate 5,5-Dioxide (3f): Rf = 0.39 (petroleum ether/
1
ethyl acetate, 5:1). H NMR (400 MHz, CDCl3): δ = 7.39 (s, 5 H),
7.19 (s, 1 H), 6.96–6.91 (m, 2 H), 6.81 (d, J = 9.0 Hz, 1 H), 6.10
(s, 1 H), 5.30 (s, 2 H), 4.46–4.36 (m, 2 H), 3.62 (s, 3 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 162.3, 157.1, 143.3, 138.2, 135.0,
128.70, 128.65, 128.4, 121.3, 120.1, 115.7, 111.2, 67.3, 66.7, 56.0,
55.5 ppm. HRMS (EI): calcd. for C19H17O6NS [M]+ 387.0777;
found 387.0777.
Cycloaddition Reaction with Cyclic Trifluoromethyl Ketimine 4:
Scheme 3. To allenoate 2a (0.225 mmol, 39.2 mg) in anhydrous tol-
uene (0.75 mL) was added ketimine 4 (0.15 mmol, 37.7 mg) and
Ph3P (10 mol-%, 0.015 mmol, 4.0 mg). The mixture was stirred at
room temperature for 1 h, but no reaction occurred as shown by
Benzyl 8-Methoxy-3,10b-dihydrobenzo[e]pyrrolo[1,2-c][1,2,3]oxathi-
azine-1-carboxylate 5,5-Dioxide (3g): Rf = 0.44 (petroleum ether/
1
ethyl acetate, 3:1). H NMR (400 MHz, CDCl3): δ = 7.48 (d, J = TLC. Then the mixture was heated to 50 °C overnight (12 h), and
8.7 Hz, 1 H), 7.39 (s, 5 H), 6.86 (s, 1 H), 6.65 (d, J = 8.8 Hz, 1 H), analysis by using TLC indicated full conversion. After cooling to
6.54 (s, 1 H), 6.07 (s, 1 H), 5.30 (AB q, ΔδAB = 0.09 ppm, JAB
=
room temperature, the toluene solution was directly charged on
12.1 Hz, 2 H), 4.46–4.35 (m, 2 H), 3.77 (s, 3 H) ppm. 13C NMR silica gel and purified by column chromatography (petroleum ether/
(100 MHz, CDCl3): δ = 162.8, 160.9, 151.3, 138.2, 136.1, 135.7, ethyl acetate) to afford the desired product (48.6 mg, 76% yield).
3768
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2013, 3764–3770

Synthesis of Benzo-Fused Cyclic Sulfamidate Heterocycles
Benzyl 10b-(Trifluoromethyl)-3,10b-dihydrobenzo[e]pyrrolo[1,2-c]-
[1,2,3]oxathiazine-1-carboxylate 5,5-Dioxide (5): Rf = 0.45 (petro-
leum ether/ethyl acetate, 5:1). 1H NMR (400 MHz, CDCl3): δ =
8.13 (d, J = 8.2 Hz, 1 H), 7.42–7.19 (m, 8 H), 7.07 (d, J = 8.2 Hz,
1 H), 5.15 (AB q, ΔδAB = 0.04 ppm, JAB = 12.2 Hz, 2 H), 4.81 (dd,
J = 2.2, 18.2 Hz, 1 H), 4.51 (dd, J = 1.3, 18.2 Hz, 1 H) ppm. 13C
NMR (100 MHz, CDCl3): δ = 159.9, 150.2, 143.6, 134.7, 131.4,
130.9, 130.0 (q, JC-F = 3.2 Hz), 128.7, 128.6, 128.4, 125.8, 123.8 (q,
JC-F = 285.4 Hz), 119.8, 116.2, 67.4, 57.4 ppm. HRMS (ESI): calcd.
for C19H14NO5SF3Na [M + Na]+ 448.0442; found 448.0441.
excess was determined by HPLC (Chiralcel AD-H column, iPrOH/
hexane, 18:82, 1.0 mL/min, 220 nm): t1 = 10.2 min, t2 = 13.5 min.
Ethyl 3,10b-Dihydrobenzo[e]pyrrolo[1,2-c][1,2,3]oxathiazine-1-carb-
oxylate 5,5-Dioxide (3m): Rf = 0.35 (petroleum ether/ethyl acetate,
1
5:1). H NMR (400 MHz, CDCl3): δ = 7.66 (d, J = 7.8 Hz, 1 H),
7.32–7.28 (m, 1 H), 7.17 (dt, J = 1.3, 7.8 Hz, 1 H), 7.03 (dd, J =
1.2, 8.2 Hz, 1 H), 6.86–6.85 (m, 1 H), 6.14 (d, J = 3.9 Hz, 1 H),
4.44–4.41 (m, 2 H), 4.38–4.30 (m, 2 H), 1.36 (t, J = 7.1 Hz, 1 H)
ppm. 13C NMR (100 MHz, CDCl3): δ = 162.4, 149.8, 137.4, 135.4,
129.4, 127.3, 126.0, 120.7, 119.2, 66.6, 61.6, 55.9, 14.1 ppm. HRMS
(EI): calcd. for C13H13O5NS [M]+ 295.0514; found 295.0517.
HPLC (Chiralcel AD-H column, iPrOH/hexane, 18:82, 1.0 mL/
min, 220 nm): t1 = 7.3 min, t2 = 8.2 min.
Gram-Scale Procedure for [3+2] Cycloaddition Reaction of Allenoate
2a and Cyclic Imine 1a: Scheme 4. To allenoate 2a (7.8 mmol,
1.359 g) in anhydrous toluene (13 mL) were added imine 1a
Supporting Information (see footnote on the first page of this arti-
cle): Data for cyclic imines, X-ray structure for product 3a and
(1.191 g,
6.5 mmol)
and
triphenylphosphane
(5 mol-%,
0.325 mmol, 85 mg). The mixture was stirred at room temperature
for 4 h, and imine 1a was shown to have reacted by using TLC.
The crude reaction mixture was directly charged on silica gel and
purified by column chromatography (petroleum ether/ethyl acet-
ate). Recrystallisation from petroleum ether/ethyl acetate gave 3a
as a white solid (2.143 g, 92%).
1
copies of the H and 13C NMR spectra for all new compounds.
Acknowledgments
We are grateful for the financial support from the National Natural
Science Foundation of China (No. 21002022), the Chinese Ministry
of Education (the Scientific Research Foundation for the Returned
Overseas Chinese Scholars), and the postdoctoral science founda-
tion supports of Henan province in China. We also thank Professor
Yong-Gui Zhou (DICP, CAS, China) for helpful suggestions and
support in experiments.
Benzyl Benzo[e]pyrrolo[1,2-c][1,2,3]oxathiazine-1-carboxylate 5,5-
Dioxide (6): Scheme 5. A mixture of 3a (0.2 mmol, 71 mg) and
DDQ (0.4 mmol, 91 mg) in benzene (3 mL) was heated to 120 °C
for 36 h in a sealed tube. After cooling to room temperature, the
reaction mixture was diluted with CH2Cl2 and filtered through a
short pad of silica gel. The crude product was subjected to column
chromatography on silica gel (petroleum ether/ethyl acetate) to af-
ford 6 as colorless oil (90%). If the reaction mixture was heated to
reflux for 3 d in an open flask, the yield obtained was 78%. Rf
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CDCl3): δ = 8.95 (dd, J = 1.7, 7.8 Hz, 1 H), 7.48–7.31 (m, 9 H),
6.97 (d, J = 3.4 Hz, 1 H), 5.36 (s, 2 H) ppm. 13C NMR (100 MHz,
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(7):
(Scheme 5) To a solution of 3a (0.2 mmol, 71 mg) in tetra-
hydrofuran (THF; 4 mL) was added lithium aluminum hydride
(1.2 mmol, 45.5 mg), and the mixture was stirred at room tempera-
ture for 50 min. TLC indicated full conversion of the starting mate-
rials, and the reaction was quenched with water. The aqueous layer
was extracted with ethyl acetate (3ϫ) and the combined organic
phases were washed with brine and concentrated under reduced
pressure. The residue was purified by column chromatography (pe-
troleum ether/ethyl acetate) on silica gel to a afford a colorless oil
1
(36.6 mg, 96%). Rf = 0.21 (petroleum ether/ethyl acetate, 2:1). H
NMR (400 MHz, CDCl3): δ = 7.41 (dd, J = 1.2, 8.1 Hz, 1 H), 7.36–
7.32 (m, 1 H), 7.29–7.25 (m, 1 H), 6.58 (s, 1 H), 5.12 (t, J = 6.5 Hz,
1 H), 4.29 (d, J = 0.8 Hz, 2 H), 3.40 (AB q, ΔδAB = 0.02 ppm, JAB
= 6.5 Hz, 2 H), 2.18–2.15 (m, 2 H), 2.15 (br., 1 H) ppm. 13C NMR
(100 MHz, CDCl3): δ = 148.2, 141.6, 131.6, 129.9, 128.8, 126.9,
124.5, 123.5, 66.5, 42.6, 31.4 ppm. HRMS (EI): calcd. for
C11H13O2N [M]+ 191.0946; found 191.0939.
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Eur. J. Org. Chem. 2013, 3764–3770
© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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Eur. J. Org. Chem. 2013, 3764–3770