Diene-transmissive hetero-Diels-Alder cycloaddition using cross-conjugated dioxatrienes: A novel synthesis of tetrahydropyran-fused aza-and thia-heterocycles

Article abstract of DOI:10.3987/COM-08-S(N)55

The diene-transmissive hetero-Diels-Alder methodology using cross-conjugated dioxatrienes [2-(R-methylene)propanedials] has been developed. The initial cycloaddition with electron-rich dienophiles, followed by the reactions of the resulting 1-oxadiene moiety of the monoadducts with amines and Lawesson's reagent generated 1-azadienes and 1-thiadienes. The second hetero-Diels-Alder reaction of these reactive heterodienes with dienophiles (tosyl isocyanate, diphenylketene, enones, and maleinimide) produced pyran-fused aza-and thiaheterocycles, providing a new synthetic method for these heterocycles. The Japan Institute of Heterocyclic Chemistry.

Full text of DOI:10.3987/COM-08-S(N)55

HETEROCYCLES, Vol. 76, No. 1, 2008
227
HETEROCYCLES, Vol. 76, No. 1, 2008, pp. 227 - 235. © The Japan Institute of Heterocyclic Chemistry
Received, 24th March, 2008, Accepted, 21st April, 2008, Published online, 24th April, 2008. COM-08-S(N)55
DIENE-TRANSMISSIVE HETERO-DIELS–ALDER CYCLOADDITION
USING CROSS-CONJUGATED DIOXATRIENES: A NOVEL SYNTHESIS
OF TETRAHYDROPYRAN-FUSED AZA- AND THIA-HETEROCYCLES
Takao Saito,* Satoru Kobayashi, Takashi Otani, Hideoki Iwanami, and
Takayuki Soda
Department of Chemistry, Faculty of Science, Tokyo University of Science,
Kagurazaka, Shinjuku-ku, Tokyo 162-8601, Japan. tsaito@rs.kagu.tus.ac.jp
This paper is dedicated to Professor Ryoji Noyori on the occasion of his 70th
birthday.
Abstract – The diene-transmissive hetero-Diels–Alder methodology using
cross-conjugated dioxatrienes [2-(R-methylene)propanedials] has been developed.
The initial cycloaddition with electron-rich dienophiles, followed by the reactions
of the resulting 1-oxadiene moiety of the monoadducts with amines and
Lawesson’s reagent generated 1-azadienes and 1-thiadienes. The second
hetero-Diels–Alder reaction of these reactive heterodienes with dienophiles (tosyl
isocyanate, diphenylketene, enones, and maleinimide) produced pyran-fused aza-
and thiaheterocycles, providing a new synthetic method for these heterocycles.
Sequential (tandem, domino, or cascade)1 transformation methodologies are efficient, valuable, and
elegant means for organic synthesis. The Diels–Alder (DA) reaction is one of the most useful and
important tools for the synthesis of a wide range of six-membered cyclic compounds because it gives a
straightforward and potentially powerful construction of such products with predictable and highly
controlled regio- and stereochemistry.2 Therefore, sequential methodologies involving such cycloaddition
reactions in the procedure1f,g,k are useful and attractive tools for the highly regio- and stereocontrolled
synthesis of cyclic compounds. The diene-transmissive Diels–Alder (DTDA) reaction represents one of
these tandem cycloaddition–transformation methods.3 Tsuge, Kanemasa, and Wada et al. and other
groups have developed this DTDA methodology using cross-conjugated carbotrienes and equivalents
capable of double 4π participation for the synthesis of bicyclo[3.3.0]decene systems.4 However, a very
limited number of examples of the diene-transmissive hetero-Diels–Alder (DTHDA) methodology have

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HETEROCYCLES, Vol. 76, No. 1, 2008
been reported so far, despite its high potential for the construction of ring-fused heterocyclic systems.5–10
The first reported examples of the DTHDA reaction included that of cross-conjugated thiatrienes.5,6
Tsuge et al.7 and Spino et al.8 independently demonstrated cross-conjugated oxatriene–DTHDA reactions.
We previously reported that cross-conjugated azatrienes also took part in the DTHDA reaction in the
synthesis of quinolinone, quinazolinone, and pyrimidopyridazinone derivatives.9,10 In these DTHDA
methodologies the cross-conjugated heterotrienes contain only one heteroatom; sulfur, oxygen, or
nitrogen, in each framework. No published report has appeared so far on a DTHDA reaction of
cross-conjugated trienes that contains two or more heteroatoms in the skeleton. Herein, we report that
cross-conjugated dioxatrienes [2-(R-methylene)propanedials] participate in the DTHDA cycloaddition for
synthesis of pyran-fused pyrimidine, pyridine, and thiopyran derivatives.
Cross-conjugated hetero trienes
R
1st DA 2nd DA
R
NR
S
O
X
O
O
R
R
R
R
R
R
X, Y = NR
X = NR, Y = C
X = S, Y = C
O
Y
O
Motoki
Saito
Spino
Saito
Tsuge
Because 2-(R1-methylene)propanedials (1) are anticipated to undergo an inverse electron-demand
hetero-Diels–Alder cycloaddition behaving as 1-oxabutadiene of a 4π-component activated by the other
Table 1. Initial HDA cycloaddition of 1 with electron-rich dienophiles.
R2
R2
H
R1
R1
R3
R3
O
O
O
O
1
2
Entry
1
R1
R2
Ph
Ph
R3
Ph
H
Methoda
Adduct
2a
Yield / %
Cis:trans (R1–R2)
1
2
3
4
5
6
7
8
9
1a
1a
1a
1b
1c
1d
1e
1e
1e
AcNH
A
A
B
C
C
A
D
D
B
69
40
99
75
67
42
50
44
43
–
2b
55:45
58:42
70:30
65:35
–
EtO
EtO
EtO
Ph
H
2c
AcO
BzO
Ph
H
2d
H
2e
Ph
Ph
H
2f
p-Tol
Ph
2g
–
Ph
2h
77:23
80:20
EtO
H
2i
a Method A: 30 mol% of BF3•OEt2, room temp., 13–22 h, CH2Cl2. Method B: 50 mol-fold excess of ethyl vinyl ether,
reflux in CH2Cl2, 1 h. Method C: one-pot reaction from triformylmethane, room temp., in CH2Cl2, 40 h for 2d, 50 °C,
1 h for 2e. Method D: 100 mol% of ZnCl2, room temp., 0.5–2 h, CH2Cl2.

HETEROCYCLES, Vol. 76, No. 1, 2008
229
formyl group, the initial cycloaddition with 1,1-diphenylethene, styrene, and ethyl vinyl ether were
carried out.
When the reaction of 2-(acetylaminomethylene)propanedial (1a)11 with 1,1-diphenylethene was
performed in refluxing toluene for 10 h, the corresponding [4 + 2] cycloadduct 2a12 was obtained in only
7% yield together with recovery of 1a (54%). However, reaction in the presence of BF3•OEt2 (Method A)
produced 2a in 69% yield (Table 1, Entry 1). Similarly, the BF3•OEt2-promoted reaction of 1a with
styrene gave the cycloadduct 2b in 40% yield with 55:45 ratio of cis/trans isomers (Entry 2). With ethyl
vinyl ether (excess amount) the reaction of 1a readily proceeded in refluxing dichloromethane for 1 h
(Method B) to quantitatively produce the cycloadduct 2c in 58:42 ratio of cis/trans isomers (Entry 3).
2-(Acetyloxy- and benzoyloxymethylene)propanedials (1b,c),13 generated by the acylation of
triformylmethane, also reacted with ethyl vinyl ether in a one-pot reaction to give the cycloadducts 2d,e
in good yields with cis:trans ratios of 70:30–65:35 (Method C, Entries 4 and 5).
2-(Arylmethylene)propanedials (1d,e)14 both reacted readily with 1,1-diphenylethene in the presence of
30 mol% of BF3•OEt2 (Method A) or 100 mol% of ZnCl2 (Method D) in dichloromethane at room
temperature to yield cycloadducts 2f (42%) and 2g (50%), respectively (Entries 6 and 7). Also, 1e reacted
with styrene and ethyl vinyl ether to produce cis(endo)-selectively 2h (44%) and 2i (43%), respectively
(Entries 8 and 9).
Table 2. Generation and second HDA cycloaddition of azadienes 3 with TsNCO.
R2
R3
R2
R3
H5
H5
R2
R3
H
TsNCO
or
Ph2CCO
R2
R3
H
R1
H8a
R1
H8a
R4NH2
R1
R1
O
O
or
O
O
O
TiCl4, Et3N
CH2Cl2
Ph
Ph
NR4
NR4
CH2Cl2
r t
TsN
NR4
0 °C
r t
O
O
2
3
4
5
Entry
2
R1
R2
R3
H
R4
Azadiene
3a
Adduct
4a
4′ad
Yielda / %
70c
63c
58
Cis:trans (H5–H8a)b
> 95:5
1
2c (cis)c
AcNH
AcNH
AcO
AcO
BzO
Ph
EtO
H
p-MeOC6H4
p-MeOC6H4
PhCH2
Me2N
2c (trans)c
2d (cis)
2d (cis)
2e (cis)
2f
EtO
H
3′ad
> 95:5
2
3
4
5
6
7
8
9
EtO
EtO
EtO
Ph
3b
4b
> 95:5
H
3ce
3d
4c
94
> 95:5
H
Ph
4d
46
> 95:5
Ph
Ph
Ph
Ph
Ph
p-ClC6H4
i-Pr
3e
4e
79
20:80
2f
Ph
Ph
3f
3ge
4f
62
47:53
2g
p-Tol
p-Tol
Ph
Ph
Me2N
4g
88
60:40
2g
Ph
i-Pr
3h
4h
66
45:55
2f
Ph
p-Tol
3i
5
99
72:28
1
a Isolated yield. b Cis:trans ratio determined based on H NMR integration. Ratio > 95:5 denotes that no minor trans isomer
was detected. c A mixture of isomers with cis:trans = 58:42 was used. Yields based on each isomer. d A prime mark in 3′ and
4′ denotes a trans relationship between the R1 and R2 groups. e Isolated (64% and 99% from cis-2d and 2g, respectively).

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HETEROCYCLES, Vol. 76, No. 1, 2008
The obtained monoadducts 2 having a transmitted 1-oxadiene 4π-moiety are not sufficiently reactive
towards dienophiles such as vinyl ethers, maleinimides, acrylates, and TCNE, but it was found that the
formyl group that activated in the initial HDA could be readily converted to imine and thiocarbonyl
functions. Thus, 1-azadienes 3 generated from 2 by treatment with amines in the presence of TiCl4–Et3N
were subjected to the second hetero-Diels–Alder reaction in a one-pot reaction with a reactive dienophile,
TsNCO, to produce [4 + 2] cycloadducts, pyrano[2,3-d]pyrimidines 415 in fair to good yield (Table 2). In
the cases of entries 1–4, the reactions are highly diastereo π-face-selective; only cis-isomers (H5–H8a,
based on NOESY) of 4a–d and 4′a were formed and they did not isomerize even in refluxing benzene-d6.
These facts suggest that the dienophile (TsNCO) attacked the azadiene from the bottom side to give
cis-isomers (H5–H8a) of 4a–d and 4′a, as shown in Scheme 1. In contrast, the reactions of azadienes 3e–h
produced cycloadducts 4e–h in good yields with low cis:trans selectivity and in addition, the ratios were
1
not reproducible (entries 5–8). H NMR monitoring of the isomers (e.g., 4g) revealed that in refluxing
benzene-d6 the cis:trans ratio of 67:33 for the isomers changed to 22:78 after 1.5 h and that in the
presence of some silica gel in CDCl3 at room temperature, 4g in a cis:trans ratio of 60:40 was completely
converted into the single trans isomer of 4g after one day. These facts imply that cis-4e–h are apt to
isomerize into the thermodynamically more stable trans-isomers and that the ratios for 4e–h are not
kinetically controlled ratios.
H7
EtO
H5
H5
Ph
Ph
H5
Ph
Ph
H5
R1
(OAc)
NHAc
R1
(OAc)
NHAc
H
H
H7
EtO
O
(OAc)
NHAc
H8a
H8a
H8a
EtO
O
O
O
O
from bottom
H8a
TsN
Ts N
R
N
Ts
N
NR4
R
NR4
N
N
O
TsN
Ts
N
R
O
O
C
O
H -H8a cis
4e-h
3a-d
O
4'a
H5-H8a cis
4e-h H5-H8a trans
4a-d
H5-H8a cis
5
Scheme 1
Similar results were also observed in the reaction of azadiene 3i with diphenylketene to produce [4 + 2]
cycloadducts 5 quantitatively in a cis:trans ratio of 72:28 (entry 9). No isomer 5 isomerized under the
reaction conditions.
Next, we examined the second DA reaction of 1-thiadienes 6 with several dienophiles. The monoadducts
2 were converted into 6 in the presence of a dienophile (methyl acrylate, methyl vinyl ketone, and
N-phenylmaleinimide) by slow addition of a 1,2-dichloroethane solution of Lawesson’s reagent (L.R.)
with gentle refluxing in THF for several hours, providing the bisadducts (7, 8, 9)16–18 in fair to good
yields (Table 3). The stereochemistry of the major isomer of 7 obtained from the reaction with dimethyl
acetylenedicarboxylate (Entry 1) suggests that the dienophile selectively attacks the thiadiene 6 π-facially

HETEROCYCLES, Vol. 76, No. 1, 2008
231
(72:28) from the bottom side, as shown in the Scheme. The reactions of 6b, c generated from 2a and 2′b,
with methyl acrylate and methyl vinyl ketone, respectively, produced the cycloadducts 8a, b, d with both
high endo/exo selectivity (H8–H8a cis) and diastereo π-facial selectivity (H4–H8a cis) (Entries 2, 3, and 5),
whereas the reaction of 6d with methyl acrylate showed high π-facial selectivity but moderate endo/exo
selectivity (60:40) (Entry 4). In all cases (Entries 1–5) the dienophile attacks from the bottom side of 6 as
observed above (for azadiene 3). In contrast, the reaction of 6b, e with N-phenylmaleinimide gave
unusual results in terms of the diastereo π-facial selectivity of the reaction. In the reaction of 6e, isomer 9
was exclusively formed, whereas the reaction of 6b produced the endo-isomer 9′ and exo-isomer 9″ in a
ratio of 77:23, both of which are likely to be formed arising from the top side-attack of the dienophile
onto the diene moiety. A further detailed study will be necessary to explain these observations.
Table 3. Generation and second HDA cycloaddition of thiadienes 6.
2
L.R.
R3
THF, reflux
R3
R2
R3
R2
R3
R2
H4
R1
H6
R1
R3
R2
R3
R2
H6
H6
H4
O
R1
R1
H8a
H9a
H9a
H9a
R1
H8a
H
N
Ph
O
O
COR4
E
O
O
H
O
R1
R2
+
+
H8
H
O
H
S
S
S
S
or
O
S
O
O
O
R4 C
O
E
H
E
H
H
S
N
N
N
E
O
Ph
O
O
Ph
Ph
E = CO2Me
bottom
7
endo
endo-bottom
endo-top
exo-top
8
6
9
9'
9"
Entry
2
R1
R2
R3
R4
–
Thiadiene
Adduct
Yield a / %
Endo:exob
π-Facialb
1
2
3
4
5
6
7
2g
2a
2′bc
2f
p-Tol
AcNH
AcNH
Ph
Ph
Ph
H
Ph
Ph
Ph
Ph
Ph
Ph
H
6a
6b
6c
6d
6b
6b
6e
7
65
78
88
78
60
80
74
–
72:28
> 95:5
> 95:5
> 95:5
> 95:5
> 95:5d
> 95:5e
MeO
MeO
MeO
Me
–
8a
8b
8c
8d
9a
9b
> 95:5
> 95:5
60:40
> 95:5
77:23d
> 95:5e
Ph
Ph
Ph
Ph
2a
2a
2b
AcNH
AcNH
AcNH
–
a Isolated yield. b Ratios of stereoisomers determined based on 1H NMR integration. Ratio > 95:5 denotes that no minor trans
isomer was detected. c A prime mark in 2′ denotes a trans relationship between the R1 and R2 groups. d 9:9′:9″ = 0:77:23.
e 9:9′:9″ = 100:0:0.
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special case of the DTDA reaction where one or more heteroatoms are contained within either a
triene framework or a dienophile
second DA
initial DA
skeleton or both. For DTDA reactions
of carbotrienes, see the literatures in
reference 4. For DTHDA reactions of
heterotrienes, see the literatures in references 5–10.
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−
1
173–175 °C; IR (KBr) νmax 3255, 1820, 1681, 1635 cm ; ¹H-NMR (300 MHz/CDCl3); δ 1.69 (s,
3H, Ac), 2.83 (dd, 1H, J = 5.7, 14.5 Hz, H-3'), 3.02 (dd, 1H, J = 5.2, 14.5 Hz, H-3), 4.75 (ddd, 1H,
J = 5.2, 5.7, 5.7 Hz, H-4), 5.29 (d, 1H, J = 5.7 Hz, NH), 7.21–7.38 (m, 8H, Ar), 7.40–7.48 (m, 2H,
Ar), 7.67 (s, 1H, H-6), 9.26 (s, 1H, CHO); 13C-NMR (75.5 MHz/CDCl3) δ 22.87 (CH3), 36.46 (CH2),
38.83 (CH), 85.61 (C), 118.21 (C), 125.29 (CH×2), 125.55 (CH×2), 127.60 (CH), 128.00 (CH),
128.32 (CH×2), 128.54 (CH×2), 141.97 (C), 142.14 (C), 165.37 (CH), 169.78 (C), 189.03 (CH);
Anal. Calcd for C20H19NO3: C, 74.70; H, 5.96; N, 4.36.ꢀ Found: C, 74.39; H, 6.09; N, 4.45.
13. (Acyloxymethylene)propanedials (1b, c) were prepared by the reaction of triformylmethane with
acyl anhydride in the presence of a small amount of pyridine.
14. 2-(Arylmethylene)propanedials (1d, e) were prepared according to the known method: (a) Z.
Arnold, V. Král, and D. Dvorak, Tetrahedron Lett., 1982, 23, 1725. (b) D. Dvorak, D. Saman, Z.
Arnold, I. Císarova, and V. Petricek, Coll. Czech. Chem. Commun., 1992, 57, 2337.
Cycloaddition reactions of 1d and its aryl-substituted analogues with electron-rich dienophiles such
as ethyl vinyl ether have also been reported.
15. N-[7-Ethoxy-3-(4-methoxyphenyl)-2-oxo-1-(toluene-4-sulfonyl)-1,3,5,6,7,8a-hexahydro-2H-
pyrano[2,3-d]pyrimidin-5-yl]-acetamide (4a): Yellowish crystals; mp 101–103 °C; IR (KBr) νmax

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3412, 1682 cm ; H-NMR (500 MHz/CDCl3) δ 1.37 (t, 3H, J = 7.0 Hz, Me (OEt)), 1.99 (br ddd,
1H, J = 0.9, 2.0, 14.2 Hz, H-2), 2.04 (s, 3H, Ac), 2.19 (ddd, 1H, J = 4.1, 5.2, 14.2 Hz, H-3), 2.39 (s,
3H, Me (Ts)), 3.68 (dq, 1H, J = 7.0, 9.3 Hz, CH2 (OEt)), 3.75 (s, 3H, OMe), 4.38 (dq, 1H, J = 7.0,
9.3 Hz, CH2 (OEt)), 4.71 (br ddd, 1H, J = 2.0, 5.2, 7.5 Hz, H-4), 5.15 (br dd, 1H, J = 0.9, 4.1 Hz,
H-1), 6.37 (s, 1H, H-6), 6.70 (s, 1H, H-5), 6.82 (d, 2H, J = 9.0 Hz, Ar), 7.10 (d, 2H, J = 9.0 Hz, Ar),
7.14 (br d, 1H, J = 7.5 Hz, NH), 7.27 (d, 2H, J = 8.4 Hz, Ar), 8.00 (d, 2H, J = 8.4 Hz, Ar);
13C-NMR (126 MHz/CDCl3) δ 14.97 (CH3), 21.51 (CH3), 23.52 (CH3), 37.53 (CH2), 46.22 (CH),
55.36 (CH3), 64.07 (CH2), 74.30 (CH), 98.90 (CH), 109.99 (C), 114.27 (CH×2), 124.71 (CH),
127.69 (CH×2), 129.09 (CH×2), 129.14 (CH×2), 131.77 (C), 136.38 (C), 144.38 (C), 147.49 (C),
158.85 (C), 169.27 (C).
16. Dimethyl 2,2-diphenyl-4-p-tolyl-2,3,4,8a-tetrahydrothiopyrano[4,3-b]pyran-7,8-dicarboxylate
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1
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(7) (cis isomer): Colorless crystals; mp 172–173 °C; IR (KBr) νmax 1726 cm ; H-NMR (400
MHz/CDCl3) δ 2.35 (s, 3H, CH3), 2.54 (dd, 1H, J = 13.7, 13.7 Hz, H-3), 3.04 (dd, 1H, J = 3.4, 13.7
Hz, H-3'), 3.81 (br d, 1H, J = 13.7 Hz, H-4), 3.82 (s, 3H, OMe), 3.92 (s, 3H, OMe), 5.28 (s, 1H,
13
H-8a), 5.57 (s, 1H, H-5), 7.10–7.50 (m, 14H, Ar); C-NMR (100 MHz/CDCl3) δ 21.03 (CH3),
43.85 (CH2), 45.29 (CH), 52.35 (CH3), 53.18 (CH3), 67.65 (CH), 81.70 (C), 110.55 (CH), 124.55
(CH×2), 126.51 (CH), 127.45 (CH), 127.49 (CH), 127.70 (CH), 128.07 (CH×2), 128.57 (CH),
128.78 (CH×2), 129.69 (C), 133.78 (C), 135.96 (C), 137.17 (C), 141.43 (C), 147.64 (C), 163.73
(C); EIMS (m/z) 512 (M+, 4).
17. 4-Acetylamino-2,2-diphenyl-3,4,8,8a-tetrahydro-2H,7H-thiopyrano[4,3-b]pyran-8-carboxylic
acid methyl ester (8a): Colorless crystals; mp 236–238 °C; IR (KBr) νmax 3247, 1812, 1735, 1643
−
1
1
cm ; H-NMR (300 MHz/CDCl3) δ 1.78 (dd, 1H, J = 12.7, 13.3 Hz, H-3'), 2.06 (s, 3H, Ac),
2.86–2.99 (m, 2H, H-8 & H-7), 3.06 (dd, 1H, J = 4.0, 13.3 Hz, H-3), 3.22 (dd, 1H, J = 3.3, 13.1 Hz,
H-7’), 3.79 (s, 3H, MeO), 4.25 (d, 1H, J = 4.4 Hz, H-8a), 5.01 (ddd, 1H, J = 4.0, 8.4, 12.7 Hz, H-4),
5.43 (d, 1H, J = 8.4 Hz, NH), 6.01 (s, 1H, H-5), 7.07–7.19 (m, 2H, Ar), 7.19–7.32 (m, 4H, Ar),
13
7.34–7.46 (m, 4H, Ar); C-NMR (75.5 MHz/CDCl3) δꢀ23.26 (CH2), 23.37 (CH3), 45.27 (CH2),
46.47 (CH), 49.28 (CH), 51.70 (CH3), 65.70 (CH), 81.22 (C), 113.14 (CH), 124.64 (CH×2), 126.60
(CH), 127.66 (CH×2), 128.01 (CH×2), 128.46 (CH), 128.85 (CH×2), 132.08 (C), 141.68 (C),
147.39 (C), 169.47 (C), 171.55 (C); Anal. Calcd for C24H25NO4S: C, 68.06; H, 5.95; N, 3.31.ꢀ
Found: C, 67.85; H, 6.08; N, 3.27.
18. N-(1,3-Dioxo-2,8-diphenyl-1,2,3,3a,7,8,9a,9b-octahydro-6H-9-oxa-4-thia-2-aza-cyclopenta[a]-
naphthalen-6-yl)acetamide (9b): Colorless crystals; mp 112–114 °C; IR (KBr) νmax 3262, 1781,
−
1
1712, 1658 cm ; 1H-NMR (600 MHz/CDCl3) δ 1.77 (ddd, 1H, J = 11.1, 11.3, 12.8 Hz, H-7'), 2.05
(s, 3H, Ac), 2.28 (ddd, 1H, J = 2.6, 5.3, 12.8 Hz, H-7), 4.02 (dd, 1H, J = 4.6, 9.4 Hz, H-9b), 4.08 (d,

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1H, J = 1.2, 9.4 Hz, H-3a), 4.87 (dd, 1H, J = 2.3, 4.6 Hz, H-9a), 5.08 (dddd, 1H, J = 2.3, 5.5, 8.8,
11.3 Hz, H-6), 5.49 (d, 1H, J = 8.8 Hz, NH), 5.58 (dd, 1H, J = 2.6, 11.1 Hz, H-8), 6.33 (d, 1H, J =
1.2 Hz, H-5), 7.27–7.33 (m, 3H, Ar), 7.37 (dd, 2H, J = 7.7, 7.7 Hz, Ar), 7.39–7.43 (m, 3H, Ar),
7.49 (dd, 2H, J = 7.8, 7.8 Hz, Ar); 13C-NMR (150 MHz/CDCl3) δ 23.27 (CH3), 37.62 (CH2), 43.47
(CH), 47.76 (CH), 51.19 (CH), 74.57 (CH), 75.00 (CH), 115.36 (CH), 126.12 (CH×2), 126.66
(CH×2), 127.99 (CH), 128.56 (CH×2), 129.03 (CH), 131.35 (C), 141.33 (C), 141.45 (C), 169.67
(C), 174.09 (C), 174.52 (C); HRMS (ESI): Calcd for C24H22N2NaO4S: [M+Na]+ 457.1199, Found:
457.1207.