MoO2Cl2(dmf)2-catalyzed domino reactions of ω-nitro alkenes to 3,4-Dihydro-2 H -1,4-benzothiazines and Other Heterocycles

Article abstract of DOI:10.1055/s-0030-1258119

Using the transformation of allyl 2-nitrophenyl thioethers to 3,4-dihydro-2H-1,4-benzothiazines as an example the reductive cyclization of -nitroalkenes to saturated N-heterocycles can be performed highly selective and with high yields if a combination of

Full text of DOI:10.1055/s-0030-1258119

1766
LETTER
MoO2Cl2(dmf)2-Catalyzed Domino Reactions of w-Nitro Alkenes to
3,4-Dihydro-2H-1,4-benzothiazines and Other Heterocycles
Domino
R
eaction
h
s
of
w
-Nitro
a
A
lkenes to
n
3,4-Dihydro
d
-2
H
-1,4-ben
i
z
othiazines C. Malakar, Elena Merisor, Jürgen Conrad, Uwe Beifuss*
Bioorganische Chemie, Institut für Chemie, Universität Hohenheim, Garbenstr. 30, 70599 Stuttgart, Germany
Fax +49(711)45922951; E-mail: ubeifuss@uni-hohenheim.de
Received 6 April 2010
clization product by (EtO)3PO formed through oxidation
of (EtO)3P during the course of the reaction. In many cas-
es, however, we were able to control the formation of
these side products by running the reductive cyclizations
Abstract: Using the transformation of allyl 2-nitrophenyl thio-
ethers to 3,4-dihydro-2H-1,4-benzothiazines as an example the re-
ductive cyclization of w-nitroalkenes to saturated N-heterocycles
can be performed highly selective and with high yields if a combi-
nation of MoO2Cl2(dmf)2 as a catalyst and Ph3P as reducing agent in toluene as solvent. Nevertheless we searched for alter-
are employed.
native reagents and reaction conditions in order to de-
crease the excess of the reagent, to increase yields and to
Key words: catalysis, domino reaction, heterocycles, nitroso ene
reaction, reductive cyclization
exclude the risk of side product formation.2
Herein, we report on the development of a new catalytic
system based on Ph3P as a reductant and a molybdenum
complex as the catalyst. It allows for the reductive cy-
clization of w-nitroalkenes to saturated N-heterocycles in
high yields without interfering formation of side products.
The so far unknown transformation of allyl 2-nitrophenyl
thioethers 7 to 3-isopropenyl-3,4-dihydro-2H-1,4-ben-
zothiazines 8 (Figure 1) was taken as an example since
many heterocycles containing a 3,4-dihydro-2H-1,4-ben-
zothiazine moiety are well known for their pronounced
biological activity.3
Recently we have reported on a new reductive cyclization
of w-nitroalkenes for the efficient synthesis of saturated
N-heterocycles using (EtO)3P as a reagent.1 By employing
the new domino transformation we were able to convert 2-
nitrophenyl ethers 1 into 3,4-dihydro-2H-1,4-benzox-
azines 2, N-allyl 2-nitroanilines 3 into 1,2,3,4-tetrahydro-
quinoxalines 4, and 1-(4-methylpent-3-enyl)-2-nitro-
benzene 5 into 1,2,3,4-tetrahydroquinoline 6 (Figure 1).
We assume that the domino process starts with the
(EtO)3P-mediated reduction of the nitro group to yield the
nitroso group which then reacts as the enophile in an in-
tramolecular ene reaction with the alkene moiety as the
ene to afford a cyclic hydroxyl amine. The final step of the
process is the (EtO)3P-mediated reduction of the NOH
group giving the corresponding saturated cyclic amine.
Given our present state of knowledge we cannot exclude
that the reaction involves a nitrene as an intermediate.
R2
NO2
(a) NaH (1.5 equiv), 0 °C,
R1
NO2
SH
R1
R3
30 min
(b) 10, THF, 2.5 h, 0 °C to r.t.
S
9
88%
85%
89%
89%
7a R1 = H, R2 = R3 = Me
7b R1 = H, R2 = Me, R3 = H
7c R1 = H, R2 = R3 = H
7d R1 = R2 = R3 = Me
R1
R3
Scheme 1
NO2
H
N
R2
The preparation of the allyl-2-nitrophenyl thioethers 7a–d
can be achieved easily by reacting the aromatic thiols 94
with the allylic bromides 10a–c under basic conditions in
yields ranging from 85–89% (Scheme 1).5
X
X
1 X = O
2 X = O
3 X = NR4
5 X = CH2
7 X = S
4 X = NR4
6 X = CH2
8 X = S
To start with, the allyl-2-nitrophenyl thioether 7a was re-
acted with 6 equivalents (EtO)3P under varying reaction
conditions (Table 1). It was no big surprise that in most
cases mixtures of 8a, and the N-ethylated product 11a was
obtained regardless of whether the reaction was per-
formed under reflux, in a sealed tube or under microwave
conditions (Table 1, entries 1–4). Complete suppression
of 11a was possible only when the transformation was run
in toluene as a solvent under microwave conditions
(Table 1, entry 5).
Figure 1
In order to obtain the products of the reductive cyclization
with the highest possible yields it was necessary to em-
ploy a six fold excess of (EtO)3P. Another problem linked
to the use of (EtO)3P is the formation of N-ethylated side
products originating from N-ethylation of the actual cy-
SYNLETT 2010, No. 12, pp 1766–1770
Advanced online publication: 30.06.2010
DOI: 10.1055/s-0030-1258119; Art ID: G11110ST
x
x
.x
x
.2
0
1
0
Further experiments revealed that (EtO)3P can be replaced
by Ph3P (Table 2). Of course, the advantage of Ph3P is that
© Georg Thieme Verlag Stuttgart · New York

LETTER
Domino Reactions of w-Nitro Alkenes to 3,4-Dihydro-2H-1,4-benzothiazines
1767
Table 1 Cyclization of 7a with (EtO)3P under Different Reaction
Conditions
First, the molybdenum-catalyzed reductive cyclization of
7a with Ph3P was studied (Table 3). When 7a was reacted
with 2.4 equivalents Ph3P in the presence of 2 mol%
MoO2Cl2(dmf)2 as a catalyst in toluene in a sealed tube for
15 hours at 185 °C, the cyclization product 8a was isolat-
ed in 63% (Table 3, entry 1). This result differs only
slightly from that of the uncatalyzed reaction. It could be
demonstrated, however, that increasing the amount of
MoO2Cl2(dmf)2 resulted in markedly improved yields.
With 5 mol% MoO2Cl2(dmf)2 the yield of 8a amounts to
80% (Table 3, entry 2); it increases to 83% with 6 mol%
MoO2Cl2(dmf)2 (Table 3, entry 3) and can be as high as
89% when 10 mol% of the catalyst are employed
(Table 3, entry 4). Then we focused on optimizing the
amount of Ph3P. It was found that reducing Ph3P from 2.4
equivalents to 1.0 equivalent significantly decreased the
yield of 8a from 89–55% (Table 3, entries 4 and 5). When
the reaction was run with 10 mol% or 250 mol%
MoO2Cl2(dmf)2 in the absence of any Ph3P the yield of 8a
dropped dramatically to 15% and 17%, respectively
(Table 3, entries 6 and 7). Due to this finding all further
experiments were performed with 2.4 equivalents of Ph3P.
The reactions of 7a,d with 2.4 equivalents of Ph3P in the
presence of catalytic amounts of MoO2Cl2(dmf)2 can also
be conducted under microwave conditions (Table 3, en-
tries 8–12). Compared to the reactions performed in
sealed vials under thermal conditions the reaction times
were reduced markedly by employing microwave radia-
tion. Under thermal conditions the transformation of 7a
with 10 mol% MoO2Cl2(dmf)2 and 2.4 equivalents Ph3P,
for example, took 15 hours to run to completion; under
microwave conditions, however, only 30 minutes were
needed. The yields of 8a were nearly identical under both
conditions (Table 3, entries 4 and 11).
R
NO2
N
P(OEt)3
S
S
7a
8a R = H
11a R = Et
Entry (EtO)3P Solvent Conditions11
(equiv)
Yield of Yield of
8a (%)a 11a (%)a
1
2
3
4
5
6.0
6.0
6.0
6.0
6.0
–
reflux, 157 °C, 5 h
sealed tube, 185 °C, 12 h 35
MW,b 200 °C, 0.5 h
65
sealed tube, 185 °C, 12 h 64
MW,b 200 °C, 0.5 h
74
68
5
40
8
–
–
C7H8
C7H8
12
–
a Isolated yield.
b Irradiations with microwaves were performed at 300 W and 20 bar
using a DiscoverTM by CEM.
Table 2 Cyclization of 7a with Ph3P under Different Conditions
H
NO2
N
Ph3P, C7H8
S
S
7a
8a
Entry
Ph3P
Conditions
Yield of 8a (%)a
(equiv)
1
2
3
4
6.0
6.0
2.4
2.4
sealed tube, 185 °C, 15 h
MW,b 200 °C, 0.75 h
sealed tube, 185 °C, 15 h
MW,b 200 °C, 1.25 h
55
54
55
47
In addition to the reactions with Ph3P a number of other
P(III) compounds were tested as reducing agents. It was
found that the transformations with polymer-bound Ph3P
as well as (n-Bu)3P also resulted in the selective formation
of 8a. Further experiments revealed that the
MoO2Cl2(dmf)2-catalyzed reaction of 7a with Ph3P can-
not only be run in toluene but in other solvents as well. In
addition to several aromatic solvents (benzene, mesity-
lene, cumene, diisopropyl benzene, and chlorobenzene)
these also include some ethers (THF and 1,4-dioxane) and
dipolar aprotic solvents (MeCN and DMF). It is notewor-
thy that the reaction does not work in polar protic sol-
vents. As the best yields of 8a14 were achieved in toluene
it remained the solvent of choice.
a Isolated yield.
b Irradiations with microwaves were performed at 300 W and 20 bar
using a DiscoverTM by CEM.
the N-ethylated product 11a cannot occur. Another advan-
tage is that the amount of Ph3P can be reduced from 6.0
equivalents to 2.4 equivalents, corresponding to an excess
of the reagent of only 20% (Table 2, entries 3 and 4). The
problem of the formation of N-ethylated products could
be solved by using Ph3P as a reagent, but the yields of 8a
remained unsatisfactory (47–55%). Thus, further options
were tested to run the reaction more efficiently. Recently,
it has been reported that MoO2Cl2(dmf)2 can be used to
catalyze the Cadogan cyclization of 2-nitrobiphenyl to
carbazoles with Ph3P,6 the deoxygenation of sulfoxides to
sulfides with phosphites7 and the reduction of N-oxides
with Ph3P.8 Against this background we studied the reduc-
tive cyclization of allyl-2-nitrophenyl thioethers 7 with
several P(III) reagents in the presence of catalytic
amounts of MoO2Cl2(dmf)2.7,9
As a result, two standard procedures were developed to be
applied in most of the transformations described. Accord-
ingly, the substrate of choice was reacted with 10 mol%
MoO2Cl2(dmf)2 and 2.4 equivalents Ph3P in toluene at
185 °C in a sealed tube or under MW conditions at
200 °C. Under these conditions the allyl thioethers 7b and
7c with differently substituted allyl groups were reacted
(Table 4). No problems were encountered in the reductive
cyclization of the (E)-2-butenyl thioether 7b which af-
forded the corresponding vinyl derivate 8b with yields of
Synlett 2010, No. 12, 1766–1770 © Thieme Stuttgart · New York

1768
C. C. Malakar et al.
LETTER
Table 3 The MoO2Cl2(dmf)2/Ph3P-Catalyzed Cyclization of 7a,d10,12,13,14
H
NO2
R
R
N
MoO2Cl2(dmf)2, Ph3P
C7H8
S
S
7a,d
8a,d
Entry
1
7
MoO2Cl2(dmf)2 (mol%) Ph3P (equiv)
Conditions
Yield of 8 (%)a
7a
7a
7a
7a
7a
7a
7a
7a
7a
7a
7a
7d
2
5
2.4
2.4
2.4
2.4
1.0
–
sealed tube, 185 °C, 12 h
sealed tube, 185 °C, 15 h
sealed tube, 184 °C, 10 h
sealed tube, 185 °C, 15 h
sealed tube, 185 °C, 15 h
sealed tube, 185 °C, 15 h
sealed tube, 184 °C, 3 h
MW,b 200 °C, 4 h
63
80
83
89
55
15
17
77
76
73
88
76
2
3
6
4
10
10
10
250
6
5
6
7
–
8
2.4
2.4
2.4
2.4
2.4
9
6
MW,b 200 °C, 2 h
10
11
12
6
MW,b 200 °C, 0.5 h
MW,b 200 °C 0.5 h
10
10
MW,b 200 °C, 0.5 h
a Isolated yield.
b Irradiations with microwaves were performed at 300 W and 20 bar using a DiscoverTM by CEM.
69% and 68%, respectively (Table 4, entries 1 and 2). In And finally it could be demonstrated that apart from 3,4-
contrast, the allyl thioether 7c did not react at all (Table 4, dihydro-2H-1,4-benzothiazines other heterocycles can be
entries 3 and 4).
made accessible by the catalytic system presented here
(Table 5). For example, the reaction of the 2-nitrophenyl
ally ether 1a afforded the 3,4-dihydro-2H-1,4-benzox-
azine 2a. The cyclization can be managed in a sealed vial
under both thermal and microwave conditions; 2a was
isolated with yields of 84% and 86%, respectively
(Table 5, entries 1 and 2). Analogous reactions of 1b de-
These results indicate that the reductive cyclizations pre-
sented here follow an Alder–ene reaction mechanism
since the alkene moiety of 7c cannot act as an ene in an
Alder–ene reaction.
Table 4 The MoO2Cl2(dmf)2-Catalyzed Reductive Cyclization of 7b,c10,12
R1
H
N
R2
NO2
cat. MoO2Cl2(dmf)2
Ph3P (2.4 equiv), C7H8
R2
S
S
7b R1 = Me, R2 = H
7c R1 = R2 = H
8b R2 = H
Entry
7
MoO2Cl2(dmf)2
Conditions
Product
Yield (%)a
(mol%)
1
7b
7b
7c
7c
10
10
6
sealed tube, 185 °C, 15 h
MW,b 200 °C, 0.5 h
8b
8b
–
68
69
–
2
3
sealed tube, 185 °C, 10 h
MW,b 200 °C, 0.5 h
4
6
–
–
a Isolated yield.
b Irradiations with microwaves were performed at 300 W and 20 bar using a DiscoverTM by CEM.
Synlett 2010, No. 12, 1766–1770 © Thieme Stuttgart · New York

LETTER
Domino Reactions of w-Nitro Alkenes to 3,4-Dihydro-2H-1,4-benzothiazines
1769
(4) Courtin, A.; von Tobel, H.-R.; Auerbach, G. Helv. Chim.
Acta 1980, 63, 1412.
(5) Mohri, K.; Suzuki, K.; Usui, M.; Isobe, K.; Tsuda, Y. Chem.
Pharm. Bull. 1995, 43, 159.
(6) Sanz, R.; Escribano, J.; Pedrosa, M. R.; Aguado, R.; Arnáiz,
F. J. Adv. Synth. Catal. 2007, 349, 713.
livered the 3,4-dihydro-2H-1,4-benzoxazine 2b in 63%
and 65% yield, respectively (Table 5, entries 3 and 4).
Also, 1,2,3,4-tetrahydroquinolines 6 can be produced by
reacting 5, as could be demonstrated using the cycliza-
tions of 5a to 6a as an example (Table 5, entries 5 and 6).
(7) Sanz, R.; Escribano, J.; Aguado, R.; Pedrosa, M. R.; Arnáiz,
F. J. Synthesis 2004, 1629.
(8) Sanz, R.; Escribano, J.; Fernández, Y.; Aguado, R.; Pedrosa,
Table 5 The MoO2Cl2(dmf)2-Catalyzed Reductive Cyclization of
1a,b and 5a
M. R.; Arnáiz, F. J. Synlett 2005, 1389.
H
N
R2
R1
(9) Butcher, R. J.; Gunz, H. P.; Maclagan, R. G. A. R.; Powell,
H. K. J.; Wilkins, C. J.; Hian, Y. S. J. Chem. Soc., Dalton
Trans. 1975, 1223.
NO2
MoO2Cl2(dmf)2 (10 mol%)
Ph3P (2.4 equiv), C7H8
R2
X
(10) General Procedure for the Synthesis of Thioethers 7a–d
In an oven dried 250 mL three-necked round-bottom flask
2-nitro thiophenol 9 (16.11 mmol) was dissolved in freshly
distilled dry THF (50 mL) under Ar. Sodium hydride (80%)
(24.16 mmol) was added in several portions at 0 °C during
10 min, and after complete addition the reaction mixture was
stirred for 30 min at 0 °C. Freshly distilled allyl bromide
(64.44 mmol) was added dropwise at 0 °C; after complete
addition the reaction mixture was allowed to stir at r.t. for
12.5 h. Then the reaction mixture was poured into sat. NH4Cl
(100 mL) and extracted with TBME (3 × 100 mL). The
combined organic phases were washed with brine (100 mL)
and dried over anhyd MgSO4. The solvents were removed
under reduced pressure, and the crude product was purified
by Kugelrohr distillation or by flash column chromatog-
raphy on silica gel (cyclohexane–EtOAc, 20:1).
X
1a R1 = Me, R2 = Me, X = O
1b R1 = Me, R2 = H, X = O
5a R1 = Me, R2 = Me, X = CH2
2a R2 = Me
2b R2 = H
6a R2 = Me
Entry
Substrate Conditions
Product Yield
(%)a
1
2
3
4
5
6
1a
1a
1b
1b
5a
5a
sealed tube, 185 °C, 15 h
2a
2a
2b
2b
6a
6a
84
86
63
65
64
63
MW,b 200 °C, 0.5 h
sealed tube, 185 °C, 15 h
MW,b 200 °C, 0.5 h
sealed tube, 185 °C, 15 h
MW,b 200 °C, 0.5 h
(11) General Procedure for the (EtO)3P-Mediated Domino
Reaction under Microwave Conditions
A 10 mL process vial was charged with a mixture of 7 (1
mmol), (EtO)3P (1.07 mL, 6 mmol) and toluene (3 mL). The
vial was sealed, placed into the cavity of the microwave
reactor, and irradiated with microwaves at 200 °C for 30–35
min, after removing (EtO)3P and (EtO)3PO by Kugelrohr
distillation under reduced pressure, the remaining residue
was diluted with hot EtOAc (50 mL). The organic phase was
washed with brine (3 × 20 mL) and dried over MgSO4.
Solvent was removed under reduced pressure, and the
remaining residue was purified by flash chromatography on
silica gel (cyclohexane–EtOAc, 20:1).
a Isolated yield.
b Irradiations with microwaves were performed at 300 W and 20 bar
using a DiscoverTM by CEM.
To summarize, the efficient synthesis of 3,4-dihydro-2H-
1,4-benzothiazines 8, 4-dihydro-2H-1,4-benzoxazines 2,
and 1,2,3,4-tetrahydroquinolines 6 by reductive cycliza-
tion of the corresponding w-nitroalkenes 7, 1, and 3 can be
achieved by employing a catalytic system based on Ph3P
as a reductant and MoO2Cl2(dmf)2 as a catalyst. The
molybdenum-catalyzed transformations with Ph3P are
characterized by being superior to the uncatalyzed trans-
formations with (EtO)3P in both selectivity and yields.
(12) General Procedure for the Mo(VI)-Catalyzed Domino
Reaction under Microwave Conditions with Ph3P as a
Reagent
A 10 mL process vial was charged with a mixture of 7 (1
mmol), Ph3P, MoO2Cl2(dmf)2, and toluene (3 mL). The vial
was sealed, placed into the cavity of the microwave reactor,
and irradiated with microwaves at 200 °C for 30–240 min,
after filtration and removal of the solvent the reaction
mixture was poured into H2O (100 mL) and extracted with
EtOAc (3 × 50 mL). The combined organic phases were
washed with brine (3 × 20 mL), dried over MgSO4, and the
solvent was removed under reduced pressure. The remaining
residue was purified by flash chromatography on silica gel
(cyclohexane–EtOAc, 20:1). Alternatively, the reaction
mixture can also be purified by flash column chroma-
tography without any workup procedure.
Acknowledgment
We thank Mrs. Dipl.-Chem. F. Mert-Balci, Dr. H. Leutbecher and
Ms. S. Mika for recording of MS and NMR spectra.
References and Notes
(1) (a) Merisor, E.; Conrad, J.; Klaiber, I.; Mika, S.; Beifuss, U.
Angew. Chem. Int. Ed. 2007, 46, 3353. (b) Merisor, E.;
Conrad, J.; Mika, S.; Beifuss, U. Synlett 2007, 2033.
(2) Merisor, E.; Beifuss, U. Tetrahedron Lett. 2007, 48, 8383.
(3) (a) Napolitano, A.; Memoli, S.; Prota, G. J. Org. Chem.
1999, 64, 3009. (b) Napolitano, A.; Di Donato, P.; Prota, G.;
Land, E. J. Free Radical Biol. Med. 1999, 27, 521.
(c) Armenise, D.; Trapani, G.; Stasi, F.; Morlacchi, F. Arch.
Pharm. Pharm. Med. Chem. 1998, 331, 54. (d) Matsuoka,
H.; Kuroki, T.; Yano, K.; Takeda, Y. J. Labelled Compd.
Radiopharm. 1997, 39, 363.
(13) Selected Data for 1-(3-Methylbut-2-enylsulfanyl)-2-
nitrobenzene (7a, Figure 2)
Rf = 0.52 (cyclohexane–EtOAc, 20:1). UV/vis (MeCN):
l
max (log e) = 245 (4.20), 380 (3.43) nm. IR (ATR): 2914,
1593, 1565, 1508, 1452, 1376, 1333, 1303, 1252, 1170,
1103, 1061, 1044, 981, 852, 780, 730 cm–1. 1H NMR (300
MHz, CDCl3): d = 1.74 (br s, 3 H, 4¢-H), 1.76 (br s, 3 H, 5¢-
H), 3.60 (d, 3J = 7.8 Hz, 2 H, 1¢-H), 5.31 (sept, 3J = 7.6 Hz,
4J = 1.4 Hz, 1 H, 2¢-H), 7.24 (ddd, 3J = 7.2 Hz, 3J = 8.2 Hz,
Synlett 2010, No. 12, 1766–1770 © Thieme Stuttgart · New York

1770
C. C. Malakar et al.
LETTER
4J = 1.4 Hz, 1 H, 4-H), 7.41 (dd, 3J = 8.2 Hz, 4J = 1.2 Hz,
1 H, 6-H), 7.54 (ddd, 3J = 7.2 Hz, 3J = 8.2 Hz, 4J = 1.5 Hz,
1 H, 5-H), 8.19 (dd, 3J = 8.2 Hz, 4J = 1.5 Hz, 1 H, 3-H).
13C NMR (75.4 MHz, CDCl3): d = 18.25 (C-5¢), 26.00 (C-
4¢), 31.27 (C-1¢), 117.18 (C-2¢), 124.65 (C-4), 126.33 (C-3),
127.29 (C-6), 133.61 (C-5), 138.80 (C-1), 139.03 (C-3’),
146.25 (C-2). MS (EI, 70 eV): m/z (%) = 223 (20) [M+], 206
(5), 155 (36), 139 (100), 138 (23), 125 (8), 117 (3), 69 (1).
HRMS (EI): m/z [M+] calcd for C11H13NO2S: 223.0667;
found: 223.0664. Anal. Calcd for C11H13NO2S: C, 59.17; H,
5.87; N, 6.27. Found: C, 59.18; H, 5.92; N, 6.62.
1107, 1075, 1033, 957, 899, 838, 738 cm–1. 1H NMR (300
MHz, CDCl3): d = 1.83 (s, 3 H, 3¢-H), 2.98 (overlapped, 1 H,
3-H), 2.98 (dd, 3J = 3.9 Hz, 2J = 12.5 Hz, 1 H, 2b-H), 3.04
(dd, 3J = 7.3 Hz, 2J = 12.5 Hz, 1 H, 2a-H), 4.08 (br dd,
3J = 3.9 Hz, 3J = 7.2 Hz, 1 H, 3-H), 5.03 (br s, 1 H, 2¢-H),
5.11 (br s, 1 H, 2¢-H), 6.54 (dd, 3J = 8.0 Hz, 2J = 1.3 Hz, 1 H,
5-H), 6.64 (ddd, 3J = 7.5 Hz, 3J = 7.5 Hz, 2J = 1.3 Hz, 1 H,
7-H), 6.93 (ddt, 3J = 7.3 Hz, 3J = 8.0 Hz, 2J = 1.6 Hz, 1 H, 6-
H), 7.02 (dd, 3J = 7.8 Hz, 2J = 1.5 Hz, 1 H, 8-H). 13C NMR
(75 MHz, CDCl3): d = 19.22 (C-3¢), 30.19 (C-2), 57.16 (C-
3), 112.95 (C-2¢), 115.66 (C-5), 115.88 (C-9), 118.5 (C-7),
125.93 (C-6), 127.74 (C-8), 142.01 (C-10), 145.81 (C-1¢).
MS (EI, 70 eV): m/z (%) = 191 (100) [M+], 163 (18), 150
(46), 117 (21), 109 (11), 65 (5). HRMS (EI): m/z [M+] calcd
for C11H13NS: 191.0769; found: 191.0783. Anal. Calcd for
C11H13NS: C, 69.07; H, 6.85; N, 7.32. Found: C, 69.15; H,
6.90; N, 7.27.
5'
NO2
3
3'
2'
4
5
2
1
4'
1'
S
6
7a
2'
H
5
N 4
1'
Figure 2
10
3'
6
7
3
2
9
S1
(14) Selected Data for 3-Isopropenyl-3,4-dihydro-2H-
benzo[1,4]thiazine (8a, Figure 3)
8
8a
Rf = 0. 54 (cyclohexane–EtOAc, 20:1). UV/vis (C2H5OH):
l
max (log e) = 230 (4.36), 313 (3.67) nm. IR (ATR): 3397,
Figure 3
2927, 1647, 1589, 1477, 1417, 1306, 1263, 1237, 1156,
Synlett 2010, No. 12, 1766–1770 © Thieme Stuttgart · New York

Copyright of Synlett is the property of Georg Thieme Verlag Stuttgart and its content may not
be copied or emailed to multiple sites or posted to a listserv without the copyright holder's
express written permission. However, users may print, download, or email articles for
individual use.