Stereoselective 1,3-dipolar cycloaddition of a maleate derivative with azomethine ylides derived from α-amino esters: Synthesis of 3-pyrrolines

Article abstract of DOI:10.1055/s-2007-977449

A new preparation of 3-pyrrolines is described by [3+2] cycloadditions of N-metalated azomethine ylides derived from α-amino esters with a dimethyl 7-oxabicyclo[2.2.1]hepta-2,5-diene-2,3-dicarboxylate derivative, followed by retro-Diels-Alder reactions. T

Full text of DOI:10.1055/s-2007-977449

1284
LETTER
Stereoselective 1,3-Dipolar Cycloaddition of a Maleate Derivative with
Azomethine Ylides Derived from a-Amino Esters: Synthesis of 3-Pyrrolines
S
ynthesis of 3-Pyr
d
rolines rien Soret,a Régis Guillot,b Gérard Rousseau,a Luis Blanco,a Sandrine Deloisy*a
a
Laboratoire de Synthèse Organique et Méthodologie, Institut de Chimie Moléculaire et des Matériaux d’Orsay (CNRS), Bât. 420,
Université Paris-Sud, 91405 Orsay Cedex, France
Fax +33(1)69156278; E-mail: sdeloisy@icmo.u-psud.fr
b
Service de Cristallographie, ICMMO (CNRS), Bât. 420, Université Paris-Sud, 91405 Orsay Cedex, France
Received 13 December 2006
efficient than the direct reaction of azomethine ylides with
dialkyl acetylenedicarboxylates which often gives moder-
ate yields, due to subsequent reactions of the pyrrolines
with the dienophiles.3,4
Abstract: A new preparation of 3-pyrrolines is described by [3+2]
cycloadditions of N-metalated azomethine ylides derived from a-
amino esters with a dimethyl 7-oxabicyclo[2.2.1]hepta-2,5-diene-
2,3-dicarboxylate derivative, followed by retro-Diels–Alder reac-
tions. This two-step sequence appears superior to the direct reaction
of ylides with dimethyl acetylenedicarboxylate and should be appli-
cable to solid-phase synthesis.
M
Ph
1)
N
CO2Me
R
CO2Me
NH
MeO2C
MeO2C
Key words: cycloadditions, amino esters, ylides, diastereoselectiv-
ity, retro reactions
R
1
+
2
2) retro-Diels–Alder
Ph
We recently reported that some N-lithiated azomethine
ylides generated from N-arylidene-a-amino esters react
unusually with dimethyl 7-oxabicyclo[2.2.1]hepta-2,5-
diene-2,3-dicarboxylate 2a (Scheme 1) to give b-amino
diesters (structural type 8, Scheme 3) instead of the ex-
pected [3+2] cycloadducts.1 The choice of the substrate
2a, prepared by reaction of dimethyl acetylenedicarboxy-
late (DMAD) with the furanic compound 1a, was justified
by the aim of a subsequent application of these reactions
in heterogeneous conditions using the polymer-supported
diester 2b (Scheme 1), as previously related in a similar
strategy.2
Scheme 2
1,3-Dipolar cycloaddition reactions of azomethine ylides
derived from imines of a-amino esters with olefins have
been extensively studied.5 Utilization of LiBr/DBU and
AgOAc/DBU are recognized to be useful conditions in
metal-catalyzed cycloadditions that can allow different
stereochemical pathways.6 Under these conditions, the
dissymmetric olefin 2a should lead, a priori, to the four
stereoisomers 4–7 by cycloaddition with the N-metalated
E,E-ylides since addition generally occurs on the exo-face
of such 7-oxabicycloheptadienic substrates (Scheme 3).
The cycloaddition reactions were run with equimolar
amounts of diester 2a and imine 3 in the presence of 1.5
equivalents of metal salt and 1.2 equivalents of DBU in
O
O
CO2Me
DMAD
OR
CO2Me
Ph
N
CO2Me
1a,b
a: R =
2a,b
R1
H
E
E
Ph
E
E
E
3
H
R1
H2C
2a
+
+
+
+
O
NH
O
NH
OR
MX, DBU, THF, 20 °C
R1
E
Ph
R2
H
R2
b: R =
H2C
R1 = H
3a:
4a–f (endo)
5a–f (endo)
3b:
3c:
3d:
3e:
3f:
R
1 = Me
R1 = i-Pr
1 = i-Bu
Scheme 1
Ph
E
H
E
E
R1
R
O
O
NH
R1
NH
R1 = Ph
R1 = 4-BzOC6H4CH2
We describe, in this communication, a two-step pathway
for the preparation of 3-pyrrolines involving [3+2] cy-
cloaddition reactions of the maleate derivative 2a with
azomethine ylides. The 3-pyrrolines were thereafter ob-
tained by retro-Diels–Alder reactions from the 1,3-dipolar
products (Scheme 2). This strategy is expected to be more
E
E
H
Ph
R2
R2
E
6a–f (exo)
7a–f (exo)
Ph
NH2
E = CO2Me
R2 = 4-BnOC6H4CH2
8:
O
CO2Me
CO2Me
SYNLETT 2007, No. 8, pp 1284–1288
Advanced online publication: 08.05.2007
1
6.
0
5.
2
0
0
7
R2
DOI: 10.1055/s-2007-977449; Art ID: D38606ST
© Georg Thieme Verlag Stuttgart · New York
Scheme 3

LETTER
Synthesis of 3-Pyrrolines
1285
tetrahydrofuran at room temperature. The structure of the
products 4–8 has been established from their NMR spec-
tra.
Table 1 Reactions of Diester 2a with Imines 3a–f
Entry Imine Reaction conditionsa Products (ratio)
Yield
(%)b
We report, in Figure 1, the selected effects in the NOESY
experiments carried out with compounds 4a,7 5a, 7d1 and
7f8 which secured their stereochemistries. The structure of
adducts 4b, 5b, 7a and 7b9 were determined by analogy of
the chemical shifts of their characteristic protons with
those of compounds 4a, 5a, 7d and 7f (see Table 2). The
characteristic protons of the minor cycloadduct 6b were
distinct from those of stereoisomers 4b, 5b and 7b and
were closer to those of isomer 7b. An exo-type structure
was thus attributed to this compound.
1
2
3
4
3a
3a
3b
3b
LiBr, DBU, 1.5 h
AgOAc, DBU, 1.5 h
LiBr, DBU, 1.5 h
AgOAc, DBU, 1.5 h
LiBr, DBU, 1.5 h
4a + 5a
(60:40)
82
86
93
74
4a + 5a + 7a
(33:18:48)
4b + 5b + 8c
(60:14:26)
7b + 6b
(85:15)
5
6
3c
3c
3d
3d
3e
3e
3f
mixture of products
–
AgOAc, DBU, 72 hd no reaction
–
7
LiBr, DBU, 2 h
8c
66
96
79
–
8
AgOAc, DBU, 2 h
LiBr, DBU, 1.5 h
AgOAc, DBU, 72 h
LiBr, DBU, 1.5 h
AgOAc, DBU, 2 h
7d
9
8c
10
11
12
no reaction
9f e
7f
66
68
3f
a Reactions were carried out in THF at r.t.
b Isolated yields after silica gel column chromatography.
c This compound was formed after hydrolysis of the reaction mixture.
See ref. 1.
d Reaction was also carried out in MeCN up to 72 h.
e The pyrroline 9f (Scheme 4) was obtained after a subsequent retro-
Diels–Alder reaction.
Figure 1 NOESY experiments for the structural determination of
exo and endo stereochemistries of the adducts.
The results, reported in Table 1, show that 1,3-dipolar cy-
cloadditions have generally occurred. In some cases, the
desired cycloadducts could not be obtained either by an
absence of reactivity in the presence of silver acetate (en-
tries 6, 10), or by an unusual reactivity of the intermediate
N-lithiated ylides previously observed1 (entries 7, 9).
Amine 8 was also present in the reaction mixture of the
LiBr-catalyzed reaction of 3b (entry 3). With the imine
3c, formed from valine, reaction in the presence of LiBr
(entry 5) led to an intractable mixture of unidentified
products.
starting furanic compound 1a was recovered. Structures
of pyrrolines were established from their NMR spectra. In
the case of R = H, the isolated 1-pyrroline 10 was proba-
bly formed by 1,3-hydrogen shifts from the related 3-pyr-
roline. This isomerization was highly stereoselective. Its
structure was unambiguously determined using HSQC,
NOESY, HMBC and INADEQUAT NMR programs.
Relative stereochemistry of 1-pyrroline 10 was confirmed
by analogy of its 1H NMR spectrum with those of similar
reported compounds.13
Interestingly the 3-pyrrolinic urea 1114 was obtained in
high yield, by reaction of the 60:40 mixture of 4a and 5a
with phenylisocyanate at room temperature. In these con-
The Ag(I)-catalyzed reactions led, mainly or exclusively,
to the cycloadducts 6 and 7 resulting from exo transition
states (entries 2, 4, 8, 12). In contrast, use of LiBr allowed
the products 4 and 5 to be obtained via endo transition
states (entries 1, 3). Such different behaviors with the 7-
oxabicycloheptadienedicarboxylate 2a could result from
different chelation sites of the lithium or the silver cation.
Pyrroline 9f, isolated after LiBr-catalyzed reaction of 3f
(entry 11), should proceed from unstable endo cycload-
duct isomer(s).
MeO2C
R
CO2Me
MeO2C
MeO2C
MeO2C
toluene
NH
H
or
+
4–7
1a
N
∆
MeO2C
H
Ph
Ph
R = H
9a (0%)
10 (72%)
(68%)
(83%)
(86%)
(82%)
R = Me
R = i-Bu
9b (82%)
9d (81%)
9f (81%)
Retro-Diels–Alder reactions of cycloadducts 4–7 were
generally run under argon in toluene at 75 °C for 16 hours.
Results, reported in Scheme 4, show the formation of pyr-
rolines 9b,10 9d,1 9f11 or 1012 in excellent yields and the
R = 4-BzOC6H4CH2
Scheme 4
Synlett 2007, No. 8, 1284–1288 © Thieme Stuttgart · New York

1286
A. Soret et al.
LETTER
Table 2 Selected Chemical Shifts (ppm) of Characteristic Protons of 1,3-Dipolar Cycloadducts
Ha
Rb
E
Rc
O
NH
Re
E = CO2Me
R = 4-BnOC6H4
E
Hf
Rd
R
Hf
4–7
Related
Assignments
4
5
6
7
Amino acid
endo
endo
exo
exo
Glycine a
Ha
4.95
5.02
4.86
Hf
3.25, 3.48a
4.41 (Hb)
4.45 (Hd)
3.47, 3.58a
4.28 (Hd)
4.72 (Hb)
2.40, 2.50a
5.28 (He)
n.d.b
PhCH
MeO2CCH
Alanine b
Leucine d
Tyrosine f
Ha
Hf
4.88
4.99
n.d.b
4.63
n.d.b
4.84
3.00–4.00a
1.96, 2.37a
PhCH
4.73 (Hb)
4.55 (Hd)
5.32 (Hc)
5.71 (He)
Ha
Hf
4.69
1.95, 2.37a
PhCH
5.53 (He)
Ha
Hf
4.77
1.95, 2.40a
PhCH
5.97 (He)
a AB system.
b Not determined.
ditions, urea formation from the 1,3-dipolar adducts in-
duced the retro-Diels–Alder reaction at
temperature (Scheme 5).
a lower
Preparation of pyrroline 9b10 requires special comments.
The high reported yield was achieved when the cyclore-
version was run in a vacuum-sealed tube for two hours to
prevent further degradation. The spectroscopic data of this
3-pyrroline are different from those of the compound pre-
pared by reaction of DMAD with imine 3b under thermal
conditions.3c The X-ray diffraction study of crystalline
compound 9b supports unambiguously our proposed
structure (Figure 2).15 In addition, we were not able to ob-
serve either the reported compound or pyrroline 9b on re-
Figure 2 ORTEP16 structure of compound 9b. Ellipsoids are drawn
producing the reported reaction. This result strengthens at the 30% probability level.
the advantage of our two-step preparation of 3-pyrrolines.
In conclusion, we describe a new sequence to prepare 3-
MeO2C
MeO2C
H
N
H
Ph
pyrrolines by reaction of ylides derived from a-amino es-
ters with dimethyl 7-oxabicyclo[2.2.1]hepta-2,5-diene-
2,3-dicarboxylate, followed by a thermal retro-Diels–
Alder reaction. This methodology could be applicable to
solid-phase employing ester-type 2b, since the thermal
stability of the [3+2] cycloadducts allows the reactants to
be removed before the thermal cycloreversion.
NHPh
O
N
C O
4a + 5a
1a
+
CH2Cl2, 20 °C
MeO2C
Ph
(84%)
11 (83%)
Scheme 5
Synlett 2007, No. 8, 1284–1288 © Thieme Stuttgart · New York

LETTER
Synthesis of 3-Pyrrolines
1287
1713, 1604, 1584, 1506, 1469, 1451, 1433, 1245, 1198,
1169, 1080, 1060 cm–1. MS (ES+): m/z (%) = 522 (100)
[pyrroline 9f + Na]+.
Acknowledgment
A. Soret thanks the French Ministry of Education and Research for
a grant. The authors express their thanks to Abdelkrim Meddour
(ICMMO) for the discussions about NMR results.
(9) Trimethyl (1S*,3S*,3aR*,4S*,7R*,7aS*)-4-[4-(Benzyl-
oxy)phenylmethyl]-1-methyl-3-phenyl-2,3,3a,4,7,7a-
hexahydro-1H-4,7-epoxyisoindole-1,3a,7a-tri-carboxy-
late (7b)
References and Notes
Oil. 1H NMR (400 MHz, CDCl3): d = 1.62 (s, 3 H), 1.96 (d,
J = 14.8 Hz, 1 H), 2.37 (d, J = 14.8 Hz, 1 H), 3.63 (s, 3 H),
3.91 (s, 3 H), 3.94 (s, 3 H), 4.21 (br s, 1 H), 4.84 (br s, 1 H),
4.94 (s, 2 H), 5.71 (s, 1 H), 5.94 (d, J = 5.2 Hz, 1 H), 6.45 (d,
J = 5.2 Hz, 1 H), 6.74 (d, J = 8.8 Hz, 2 H), 6.89 (d, J = 8.8
Hz, 2 H), 7.24–7.60 (m, 10 H). 13C NMR (100 MHz, CDCl3):
d = 21.3, 34.9, 51.7, 52.4, 52.6, 65.7, 69.2, 69.7, 69.9, 80.9,
83.0, 96.7, 113.9, 127.2, 127.6, 127.7, 128.2, 128.3, 130.3,
130.4, 130.8, 132.0, 136.9, 137.3, 145.4, 156.9, 169.3,
171.7, 171.9. IR (neat): 3450, 3062, 3032, 3003, 2951, 1744,
1726, 1654, 1611, 1511, 1454, 1434, 1249, 1225, 1079 cm–1.
MS (ES+): m/z (%) = 274 (33), 334 (100), 598 (15) [M + H]+.
HRMS (ES+): m/z calcd for C35H36O8N: 598.2435; found:
598.2453.
(1) Soret, A.; Blanco, L.; Deloisy, S. Lett. Org. Chem. 2006, 3,
648.
(2) Blanco, L.; Bloch, R.; Bugnet, E.; Deloisy, S. Tetrahedron
Lett. 2000, 41, 7875.
(3) (a) Anderson, W.; Kinder, F. R. J. Heterocycl. Chem. 1990,
27, 975. (b) Komatsu, M.; Ohno, M.; Tsuno, S.; Ohshiro, Y.
Chem. Lett. 1990, 575. (c) Grigg, R.; Gunaratne, N. H. Q.;
Kemp, J. Tetrahedron 1990, 46, 6467.
(4) For a solid-phase application of this methodology, see:
Komatsu, M.; Okada, H.; Akaki, T.; Oderaotoshi, Y.;
Minakata, S. Org. Lett. 2002, 4, 3505.
(5) (a) Pandey, G.; Banerjee, P.; Gadre, S. R. Chem. Rev. 2006,
106, 4484. (b) Husinec, S.; Savic, V. Tetrahedron:
Asymmetry 2005, 16, 2047. (c) Najara, C.; Sansano, J. M.
Curr. Org. Chem. 2003, 7, 1105. (d) Harwood, L. M.;
Vickers, R. J. In The Chemistry of Heterocyclic Compounds,
Vol. 59; Padwa, A.; Pearson, W. H., Eds.; John Wiley and
Sons: New York, 2002, 169–252. (e) Broggini, G.; Zecchi,
G. Synthesis 1999, 905. (f) Grigg, R.; Sridharan, V. In
Advances in Cycloaddition, Vol. 3; Curran, O. P., Ed.; JAI
Press: Greenwich CT, 1993, 161–204.
(10) Trimethyl (2S*,5S*)-2-Methyl-5-phenyl-2,5-dihydro-
1H-pyrrole-2,3,4-tricarboxylate (9b)
White solid; mp 62–63 °C. 1H NMR (400 MHz, CDCl3):
d = 1.66 (s, 3 H), 2.74 (br s, 1 H), 3.60 (s, 3 H), 3.80 (s, 3 H),
3.83 (s, 3 H), 5.35 (s, 1 H), 7.20–7.35 (m, 5 H). 13C NMR
(100 MHz, CDCl3): d = 24.8, 52.2, 52.4, 52.9, 69.0, 73.0,
127.4, 128.3, 128.4, 140.1, 140.9, 141.2, 163.5, 163.7,
172.9. IR (KBr): 3359, 2992, 2950, 2832, 1733, 1715, 1656,
1449, 1433, 1334, 1244, 1204 cm–1. MS (ES+): m/z
(%) = 274 (74), 334 (77) [M + H]+, 356 (100) [M + Na]+.
HRMS (ES+): m/z calcd for C17H19O6NNa: 356.1105; found:
356.1119.
(6) (a) Grigg, R.; Montgomery, J.; Somasunderam, A.
Tetrahedron 1992, 48, 10431. (b) Nyerges, M.; Rudas, M.;
Tòth, G.; Herényi, B.; Kàdas, I.; Bitter, I.; Töke, L.
Tetrahedron 1995, 51, 13321.
(11) Trimethyl (2S*,5S*)-2-[4-(Benzoyloxy)phenylmethyl]-5-
phenyl-2,5-dihydro-1H-pyrrole-2,3,4-tricarboxylate (9f)
Oil. 1H NMR (250 MHz, CDCl3): d = 2.83 (br s, 1 H), 3.32
(s, 2 H), 3.54 (s, 3 H), 3.80 (s, 3 H), 3.90 (s, 3 H), 4.68 (br s,
1 H), 7.14 (d, J = 8.5 Hz, 2 H), 7.26–7.30 (m, 5 H), 7.42 (d,
J = 8.5 Hz, 2 H), 7.46–7.52 (m, 2 H), 7.57–7.67 (m, 1 H),
8.20 (d, J = 7.0 Hz, 2 H). 13C NMR (62.9 MHz, CDCl3):
d = 42.5, 52.0, 52.5, 52.8, 69.1, 77.5, 121.1, 127.7, 128.1,
128.5, 128.6, 129.5, 130.0, 131.8, 133.1, 133.5, 140.4,
140.7, 141.1, 150.0, 162.7, 164.5, 165.0, 171.9. IR (neat):
3367, 3063, 3032, 3005, 2953, 2847, 1739, 1731, 1713,
1659, 1601, 1507, 1452, 1434, 1250, 1200, 1168, 1082,
1063, 1024 cm–1. MS (ES+): m/z (%) = 552 (100) [M + Na]+.
HRMS (ES+): m/z calcd for C30H27O8NNa: 552.1629; found:
552.1628.
(7) Trimethyl (1S*,3S*,3aR*,4R*,7S*,7aS*)-7-[4-(Benzyl-
oxy)phenylmethyl]-3-phenyl-2,3,3a,4,7,7a-hexahydro-
1H-4,7-epoxyisoindole-1,3a,7a-tricarboxylate (4a)
White solid; mp 106 °C. 1H NMR (400 MHz, CDCl3):
d = 2.93 (s, 3 H), 3.25 (d, J = 15.2 Hz, 1 H), 3.48 (d, J = 15.2
Hz, 1 H), 3.81 (s, 3 H), 3.86 (s, 3 H), 4.41 (s, 1 H), 4.45 (s, 1
H), 4.95 (s, 1 H), 5.07 (s, 2 H), 6.15 (d, J = 6.0 Hz, 1 H), 6.66
(d, J = 6.0 Hz, 1 H), 6.96 (d, J = 8.4 Hz, 2 H), 7.27 (d, J = 8.4
Hz, 2 H), 7.29–7.92 (m, 10 H). 13C NMR (100 MHz, CDCl3):
d = 35.0, 51.5, 52.0, 52.4, 66.6, 70.0, 70.1, 73.5, 82.6, 83.9,
94.5, 114.5, 127.2, 127.6, 128.1, 128.4, 128.5, 128.6, 129.3,
131.4, 133.4, 137.2, 137.8, 141.3, 157.6, 169.8, 170.9,
171.2. IR (KBr): 3307, 1744, 1731, 1609, 1581, 1511, 1452,
1431, 1245, 1222, 1106 cm–1. MS (ES+): m/z (%) = 320
(100) [pyrroline 10 + H]+, 342 (16) [pyrroline 10 + Na]+.
Anal. Calcd for C34H33NO8: C, 69.97; H, 5.70; N, 2.40.
Found: C, 69.81; H, 5.67; N, 2.27.
(12) Trimethyl (3S*,4S*,5R*)-5-Phenyl-4,5-dihydro-3H-
pyrrole-2,3,4-tricarboxylate (10)
Oil. 1H NMR (400 MHz, CDCl3): d = 3.15 (s, 3 H), 3.76 (s,
3 H), 3.87 (dd, J = 9.2, 6.0 Hz, 1 H), 3.93 (s, 3 H), 4.72 (dd,
J = 6.0, 2.4 Hz, 1 H), 5.86 (dd, J = 9.2, 2.4 Hz, 1 H), 7.05–
7.08 (m, 2 H), 7.22–7.32 (m, 3 H). 13C NMR (100 MHz,
CDCl3): d = 51.8, 52.7, 52.9, 56.5, 56.6, 78.9, 127.4, 128.2,
128.3, 135.6, 161.9, 164.0, 170.0, 170.1. IR (neat): 3059,
3033, 3007, 2956, 2919, 2847, 1726, 1648, 1452, 1437,
1369, 1312, 1258, 1217, 1101 cm–1. MS (ES+): m/z (%) =
260 (100), 342 (82) [M + Na]+. HRMS (ES+): m/z calcd for
C16H17O6NNa: 342.0948; found: 342.0955.
(8) Trimethyl (1S*,3S*,3aR*,4S*,7R*,7aS*)-1-[4-(Benzoyl-
oxy)phenylmethyl]-4-[4-(benzyloxy)phenylmethyl]-3-
phenyl-2,3,3a,4,7,7a-hexahydro-1H-4,7-epoxyisoindole-
1,3a,7a-tricarboxylate (7f)
Oil. 1H NMR (250 MHz, CDCl3): d = 1.95 (d, J = 15.0 Hz, 1
H), 2.40 (d, J = 15.0 Hz, 1 H), 3.09 (d, J = 14.0 Hz, 1 H),
3.49 (d, J = 14.0 Hz, 1 H), 3.73 (s, 3 H), 3.84 (s, 3 H), 3.99
(s, 3 H), 4.77 (d, J = 1.8 Hz, 1 H), 4.94 (s, 2 H), 5.97 (br s, 1
H), 6.00 (dd, J = 5.5, 1.8 Hz, 1 H), 6.49 (d, J = 5.5 Hz, 1 H),
6.75 (d, J = 8.8 Hz, 2 H), 6.90 (d, J = 8.8 Hz, 2 H), 7.04 (d,
J = 8.5 Hz, 2 H), 7.31–7.60 (m, 15 H), 8.15 (d, J = 7.0 Hz, 2
H). 13C NMR (62.9 MHz, CDCl3): d = 35.1, 37.1, 52.1, 52.5,
52.8, 65.2, 69.8, 70.8, 74.4, 81.7, 83.6, 96.9, 114.1, 120.9,
127.4, 127.7, 127.8, 127.9, 128.1, 128.5, 130.1, 130.4,
131.0, 131.6, 131.8, 132.5, 133.2, 133.3, 133.4, 137.1,
137.4, 145.6, 149.6, 157.1, 165.0, 169.5, 170.6, 172.9. IR
(neat): 3327, 3060, 3028, 3005, 2951, 2851, 1738, 1729,
(13) Katritzky, A. R.; Hitchings, G. J.; Zhao, X. Synthesis 1991,
863.
(14) Trimethyl (2S*,5S*)-1-(Phenylcarbamoyl)-5-phenyl-2,5-
dihydro-1H-pyrrole-2,3,4-tricarboxylate (11)
White solid; mp 156–157 °C. 1H NMR (250 MHz, CDCl3):
d = 3.69 (s, 3 H), 3.86 (s, 3 H), 3.93 (s, 3 H), 5.60 (d, J = 3.0
Hz, 1 H), 5.96 (d, J = 3.0 Hz, 1 H), 6.76 (br s, 1 H), 6.99 (t,
Synlett 2007, No. 8, 1284–1288 © Thieme Stuttgart · New York

1288
A. Soret et al.
LETTER
collected with MoKa radiation on Kappa X8 APEX II
system. Data analysis was carried out with Bruker program
SMART and SAINT,17 the structure was solved and refined
by direct methods using SHELXTL program18 to
R1 = 0.0572, wR2 = 0.1505. The supplementary
crystallographic data can be obtained free of charge from the
Cambridge Crystallographic Data Centre via
www.ccdc.cam.uk/data_request/cif. Please quote reference
number CDDC 630085.
J = 8.6 Hz, 1 H), 7.14 (d, J = 7.6 Hz, 2 H), 7.19–7.22 (m, 2
H), 7.41–7.48 (m, 3 H), 7.72 (d, J = 7.2 Hz, 2 H). 13C NMR
(62.9 MHz, CDCl3): d = 52.3, 52.6, 52.9, 67.0, 69.3, 119.2,
123.2, 127.9, 128.6, 129.1, 129.2, 131.2, 136.5, 137.8,
140.6, 152.9, 161.8, 161.9, 169.5. IR (neat): 3365, 3033,
3007, 2956, 2919, 2847, 1749, 1726, 1646, 1541, 1447,
1434, 1363, 1333, 1279, 1247 cm–1. MS (ES+): m/z (%) =
461 (100) [M + Na]+. HRMS (ES+): m/z calcd for
C23H22O7N2Na: 461.1319; found: 461.1328.
(15) X-ray Crystal Data of 9b
(16) Farrugia, L. J. J. Appl. Cryst. 1997, 30, 565.
(17) Bruker SMART and SAINT, Bruker AXS Inc., Madison,
Wisconsin, USA, 1997.
(18) Bruker SHELXTL, Version 6.3.1, Bruker AXS Inc.,
Madison, Wisconsin, USA, 2004.
C17H19NO6, M = 333.33, triclinic, space group P-1, Z = 2,
a = 6.0095 (8) Å, b = 8.1268 (13) Å, c = 18.151 (3) Å,
a = 78.363 (3)°, b = 89.035 (2)°, g = 77.285 (3)°, V = 846.6
(2) Å3, d = 1.308 g/cm3, 3217 independent reflections were
Synlett 2007, No. 8, 1284–1288 © Thieme Stuttgart · New York

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