Gold-catalyzed [2+2] cyclization of alkyne-propargylic pivaloates to fused bicyclic compounds

Article abstract of DOI:10.1055/s-2008-1032110

We discovered a new and highly convenient gold-catalyzed cyclization of alkyne-propargylic pivaloates leading to fused bicyclic compounds. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2008-1032110

CLUSTER
777
Gold-Catalyzed [2+2] Cyclization of Alkyne-propargylic Pivaloates to Fused
Bicyclic Compounds
G
old-Catalyzed[
h
2+2]
C
ycliza
a
tion of
A
lk
n
yne-proparg
g
s
Ho Oh,* Ahyun Kim
Department of Chemistry, Hanyang University, Sungdong-Gu, Seoul 133-791, Korea
Fax +82(2)22990762; E-mail: changho@hanyang.ac.kr
Received 3 December 2007
to B. The further conversion of B via demetalation (into
Abstract: We discovered a new and highly convenient gold-cata-
lyzed cyclization of alkyne-propargylic pivaloates leading to fused
bicyclic compounds.
C) and dehydrogenation afforded the tricycle 3
(Scheme 1). Yet its mechanism and the origin of hydrogen
were not clear.
Key words: gold, cyclization, pivaloate, catalyst, bicyclic com-
pounds
The present conditions toward a triyne 4a, a homologue of
1a, did not afford the expected tricycle, but exhibited a
different mode of reactions to give the [3.2.0]-bicyclic
system 7a. Herein we wish to report our results on the
scope and limitations of this new reaction leading to the
[3.2.0] and [4.2.0] bicycles 7 (Scheme 2).5 At first, we
surveyed the reaction conditions including catalysts, sol-
vent, and the reaction temperatures toward the substrate
4a (Table 1). Sodium tetrachloroaurate (NaAuCl4) was
tested in three different solvents (entries 1–3). While
NaAuCl4 in either dichloromethane at 50 °C or 1,4-diox-
ane at 80 °C was ineffective, NaAuCl4 in ethanol cata-
lyzed 4a into the allene intermediate 5a, which was
hydrolyzed to the corresponding enone 6a. The same con-
version into enone 6a was also carried out by AuBr3 in
ethanol at 80 °C (entry 4). Both AuCl/AgSbF6 and AuCl3/
AgSbF6 as cooperative catalysts in dioxane at 50 °C led to
decomposition of 4a. To our delight, 5 mol% AuCl(PPh3)
with AgSbF6 as a cocatalyst in 1,2-dichloroethane (DCE)
at room temperature converted 4a into the bicyclo[3.2.0]
compound 7a in 72% yield (entry 7). Finally, we tested
PtCl2 as a catalyst but found to be ineffective for this re-
action (entry 8). Next, we tested other structurally similar
Recent advances in gold-based alkyne activation led to
develop new and efficient catalytic reactions applicable to
the synthesis of complex molecules.1 On the behalf of the
excellent alkynophilicity of gold cations, terminal alkynes
in the presence of a nucleophile could form gold–carbene
complexes.2 Internal alkynes are weakly activated enough
to react with nucleophiles of alkenes or aldehydes. Phen-
yl-substituted alkynes, for example, might form weak p-
complexes which underwent [2+2+2] cycloaddition with
a pendent double bond and one double bond in the phenyl
ring.3 We became interested in gold-catalyzed chemistry
of triynes containing a terminal, an internal (propargylic
ester), and a phenyl-conjugated triple bond in the same
molecule.
In this context, we recently reported gold-catalyzed cas-
cade cyclization of the triyne 1 to the tricycle 3.4 Mecha-
nistically, the allene 2, the initial intermediate from 1
under the gold catalysis, would react with the terminal tri-
ple bond to form the gold-bound diene intermediate A,
which would subsequently undergo [4+2] cycloaddition
O
Ac
AcO
AcO
10 mol% AuCl(PPh3)
10 mol% AgSbF6
EDC, r.t., 3 h, 75%
–XnAu
A
Ph
Ph
Ph
2
1
O
Ac
O
O
Ac
– MeCHO
via
[+ H2O – AcOH – H2]
–XnAu
Ph
B
C
Ph
Ph
3
Scheme 1
SYNLETT 2008, No. 5, pp 0777–0781
x
x.
x
x.
2
0
0
8
Advanced online publication: 26.02.2008
DOI: 10.1055/s-2008-1032110; Art ID: Y02107ST
© Georg Thieme Verlag Stuttgart · New York

778
C. H. Oh, A. Kim
CLUSTER
O
Ph
6a
O
PivO
PivO
Ph
7a
Ph
Ph
5a
4a
expected pathway by ref. 4
O
O
Ph
Ph
3a
A'
Scheme 2
Table 2 Gold(I)-Catalyzed Cyclization of Alkyne-pivaloates 4 to
Bicyclo[m.2.0] Compounds 7 (Figure 1)
Table 1 Cyclization of 4a under Various Conditions
Entry Catalyst (5 mol%) Solvent Temp Time Product
Substrates
Temp (°C) Time (h)
Product
Yield (%)a
(°C)
(h)
(yield, %)
1
2
3
4
5
6
7
8
NaAuCl4
CH2Cl2
dioxane
EtOH
50
5
NR
OPiv
R1
NaAuCl4
80
5
NR
NaAuCl4
80
0.5
0.5
15
6a (75)
6a (74)
dec.
R2
AuBr3
EtOH
80
4b
4c
4d
4e
4f
80
40
40
25
25
25
40
40
25
15
1
7b
7c
7d
7e
7f
81
75
80
72
80
72
65
55
75
AuCl/AgSbF6
AuCl3/AgSbF6
dioxane
dioxane
50
50
15
15
15
dec.
1
AuCl(PPh3)/AgSbF6 DCE
PtCl2 toluene
25
7a (72)
NR
1
100
1.5
4g
4h
4i
2
7g
7h
7i
substrates (4b–g and 4h–j) under the optimized condi-
tions described in entry 7 in Table 1 (Table 2).6
2.5
The substrates 4b–g were smoothly transformed to the
[3.2.0] bicycles 7b–g in good yields. Substrate 4b, pos-
sessing 6-phenylhex-1-ynyl at the R1 position and phenyl
group at the R2 position furnished the desired product 7b
in 81% yield. The reactions proceeded smoothly, when
the phenyl group (4c,d) and naphthyl group (4e,f) were lo-
cated at the R2 position, affording 4c–f in 72–81% yield.
Notably, the substrate 4g containing a cyclohexyl ring at
the R2 position was successfully cyclized to 7g in 72%
yield.
15
15
4j
7j
a All reactions were carried out 5 mol% of AuCl(PPh3) and AgSbF6 in
DCE.
4l were prepared and cyclized under the present condi-
tions to give the expected products 7k and 7l in 85% and
83% yields, respectively. Surprisingly, these cyclizations
4k,l to 7k,l seemed to proceed more easily in comparison
to substrates 4a–j; this might imply that the electron-with-
drawing effect by the first cyclization might facilitate the
second cyclization.
The present conditions were successfully applied to the
substrates 4h–j affording bicyclo[4.2.0] compounds 7h,
7i, and 7j in 65%, 55%, and 75% yields, respectively.
Next, we have extended further this reaction to two
alkyne-pivaloate groups in a molecule linked by a phenyl
group to obtain the corresponding dimeric bicycles for
useful building blocks (Scheme 3). Both substrates 4k and
A possible mechanism for gold-catalyzed cyclization of
alkyne-proparglic pivaloate 4a to 7a is proposed
(Scheme 4).
Synlett 2008, No. 5, 777–781 © Thieme Stuttgart · New York

CLUSTER
Gold-Catalyzed [2+2] Cyclization of Alkyne-propargylic Pivaloates
779
OPiv
OPiv
OPiv
Ph
n-Bu
Ph
Ph
4c
Ph
4b
Ph
4d
OPiv
OPiv
OPiv
n-Bu
1-Np
Ph
1-Np
Ph
4e
4g
4f
OPiv
OPiv
OPiv
n-Bu
Ph
n-Bu
Ph
4j
Ph
Ph
4i
4h
O
O
O
Ph
O
n-Bu
Ph
Ph
Ph
Ph
O
7b
7c
7d
O
Ph
n-Bu
1-Np
O
1-Np
Ph
7e
7f
7g
O
O
n-Bu
Ph
n-Bu
Ph
Ph
Ph
7j
7h
7i
Figure 1
O
PivO
OPiv
Bu
AuCl(PPh3),
AgSbF6 (10 mol%)
Bu
Bu
DCE, r.t., 0.5 h
Bu
7k (85 %)
O
4k
O
PivO
OPiv
Ph
Ph
Ph
AuCl(PPh3),
AgSbF6 (10 mol%)
DCE, r.t., 1 h
Ph
O
7l (83 %)
4l
Scheme 3
Coordination of gold(I) to propargylic alkyne induced mi- directly cycloadded via a [2+2] pathway to give the inter-
gration of the pivaloate to give the allene intermediate A. mediate F, which would afford the isolated product 7a
The allene A was expected to undergo condensation with upon hydrolysis.
one of the gold-activated triple bonds, path a and b. The
isolation of 7a and no formation of 3a might suggest the
intermediacy of C via path b. Intermediate C could elim-
inate pivaloic acid by addition of H2O to form D. Finally,
cyclization of D into E might be postulated, although such
a cyclization is not known. Instead, the allene A could be
In conclusion, we discovered a highly convenient gold-
catalyzed cyclization of alkyne-propargylic pivaloates
leading to [m.2.0] bicyclic compounds, that could provide
an easy access to valuable building blocks for polycyclic
compounds.
Synlett 2008, No. 5, 777–781 © Thieme Stuttgart · New York

780
C. H. Oh, A. Kim
CLUSTER
PivO
OPiv
PivO
" Au(I) "
via [2+2]
b
a
Ph
Au(I)
Ph
Ph
F
Au(I)
path a
4a
A
path b
O
OPiv
O
PivO
H2O
Ph
+
Ph
Ph
Au(0)
Ph
PivOH
7a
Au(0)
Au(0)
B
C
Au(I)
Au(I)
H2O
PivOH
O
O
O
Au(0)
Ph
Ph
Ph
Au(0)
3a
D
E
Scheme 4
being stirred for 10 min at 0 °C, a DCE solution (0.5 mL) of
diyne-propargylic pivaloate 4a (101.0 mg, 0.28 mmol) was
added. The resulting mixture was stirred for 15 h at r.t. and
the reaction was periodically monitored by TLC. Upon
completion, the solvent was removed under vacuum and the
crude product was subjected to flash column chroma-
tography (SiO2, n-hexane–EtOAc = 30:1) to afford the pure
product 7a as a colorless oil. All new compounds were fully
characterized by 1H NMR, 13C NMR, IR, and HRMS
(ESMS).
Compound 7a: IR (NaCl): 3301, 3064, 2940, 2869, 1707,
1671, 1491, 1287 cm–1. 1H NMR (400 MHz, CDCl3): d =
8.07–8.04 (m, 2 H), 7.42–7.37 (m, 3 H), 3.47 (q, J = 4.0 Hz,
1 H), 3.40 (q, J = 4.0 Hz, 1 H), 2.68–2.49 (m, 2 H), 2.22 (td,
J = 7.0, 3.2 Hz, 2 H), 1.95 (t, J = 2.4 Hz, 1 H), 1.83–1.68 (m,
5 H), 1.66–1.54 (m, 3 H), 1.49–1.38 (m, 3 H). 13C NMR (100
MHz, CDCl3): d = 197.13, 155.44, 136.26, 132.49, 130.25,
128.93, 128.35, 84.19, 68.46, 43.75, 43.28, 40.06, 28.01,
26.31, 26.07, 23.16, 22.72, 18.35. HRMS: m/z calcd for
C20H22ONa+: 301.3779; found: 301.3787.
Compound 7b: IR (NaCl): 3059, 3030, 2931, 2853, 2225,
1736, 1670, 1560, 1175 cm–1. 1H NMR (400 MHz, CDCl3):
d = 8.06–8.04 (m, 2 H), 7.39–7.37 (m, 5 H), 7.28–7.24 (m, 3
H), 3.45 (q, J = 3.6 Hz, 1 H), 3.39 (q, J = 3.6 Hz, 1 H), 2.71–
2.52 (m, 2 H), 2.44 (t, J = 7.6 Hz, 2 H), 1.86–1.77 (m, 4 H),
1.73–1.54 (m, 6 H), 1.48–1.38 (m, 2 H). 13C NMR (100
MHz, CDCl3): d = 197.23, 155.39, 136.35, 132.55, 131.55,
130.23, 128.94, 128.35, 128.14, 127.49, 123.97, 89.87,
80.89, 43.78, 43.33, 40.17, 28.33, 26.34, 26.09, 23.18,
22.97, 19.35. HRMS: m/z calcd for C26H26ONa+: 377.4733;
found: 377.4778.
Compound 7c: IR (NaCl): 3065, 3030, 2945, 2857, 2247,
1797, 1634, 1490, 1228, 1172 cm–1. 1H NMR (400 MHz,
CDCl3): d = 7.88 (d, J = 3.8 Hz, 2 H), 7.57–7.54 (m, 2 H),
7.49 (t, J = 7.2 Hz, 1 H), 7.38 (t, J = 7.2 Hz, 2 H), 7.28–7.23
(m, 3 H), 3.64–3.56 (m, 2 H), 1.87–1.78 (m, 2 H), 1.74–1.63
(m, 2 H), 1.52–1.46 (m, 1 H), 1.42–1.32 (m, 1 H). 13C NMR
(100 MHz, CDCl3): d = 191.46, 153.85, 138.08, 136.24,
132.54, 132.40, 129.54, 128.94, 128.69, 128.39, 128.19,
45.69, 44.53, 26.49, 26.27, 23.29 29. HRMS: m/z calcd for
Acknowledgment
We wish to acknowledge the financial support of Korea Science and
Engineering Foundation (R01-2007-000-20315-0).
References and Notes
(1) For reviews, see: (a) Hashmi, A. S. K.; Hutchings, G. J.
Angew. Chem. Int. Ed. 2006, 45, 7896. (b) Gorin, D. J.;
Toste, F. D. Nature (London) 2007, 446, 395. (c) Jiménez-
Núñez, E.; Echavarren, A. M. Chem. Commun. 2007, 333.
(2) (a) Huang, X.; Zhang, L. J. Am. Chem. Soc. 2007, 129,
6398. (b) Nieto-Oberhuber, C.; Pérez-Galán, P.; Herrero-
Gómez, E.; Lauterbach, T.; Rodriguez, C.; López, S.; Bour,
C.; Rosellon, A.; Cárdenas, D. J.; Echavarren, A. M. J. Am.
Chem. Soc. 2008, 130, 269. (c) Luo, T.; Schreiber, S. L.
Angew. Chem. Int. Ed. 2007, 46, 8250. (d)Johansson, M. J.;
Gorin, D. J.; Staben, S. T.; Toste, F. D. J. Am. Chem. Soc.
2005, 127, 18002. (e) Luzung, M. R.; Markham, J. P.; Toste,
F. D. J. Am. Chem. Soc. 2004, 126, 10858. (f) Zhang, L.;
Kozmin, S. A. J. Am. Chem. Soc. 2004, 126, 11806.
(g) Zhang, L.; Kozmin, S. A. J. Am. Chem. Soc. 2005, 127,
6963. (h) C. Nieto-Oberhuber, S.; López, A. M.;
Echavarren, A. M. J. Am. Chem. Soc. 2005, 127, 6178.
(i) Fürstner, A.; Hannen, P. Chem. Commun. 2004, 2546.
(3) (a) Mézailles, N.; Ricard, L.; Gagosz, F. Org. Lett. 2005, 7,
4133. (b) Nieto-Oberhuber, C.; Muñoz, M. P.; López, S.;
Jiménez-Núñez, E.; Nevado, C.; Herrero-Gómez, E.;
Raducan, M.; Echavarren, A. M. Chem. Eur. J. 2006, 12,
1677.
(4) Oh, C. H.; Kim, A. New J. Chem. 2007, 31, 1719.
(5) For Au-catalyzed [2+2] cyclization, see: (a) Couty, S.;
Meyer, C.; Cossy, J. Angew. Chem. Int. Ed. 2006, 45, 6726.
(b) Luzung, M. R.; Mauleon, P.; Toste, F. D. J. Am. Chem.
Soc. 2007, 129, 12402.
(6) Typical Experimental Procedure for Cyclization of 4a to
7a
In a 5 mL new test tube were placed AuCl(PPh3) (7.0 mg,
14.0 mmol, 5 mol%) and AgSbF6 (4.8 mg, 14 mmol) and
added dried DCE (1.0 mL) under argon atmosphere. After
Synlett 2008, No. 5, 777–781 © Thieme Stuttgart · New York

CLUSTER
C20H18ONa+: 297.3461; found: 297.3462.
Gold-Catalyzed [2+2] Cyclization of Alkyne-propargylic Pivaloates
781
(m, 2 H), 1.66–1.58 (m, 3 H), 1.57–1.42 (m, 4 H), 1.39–1.30
(m, 2 H), 1.27–1.22 (m, 1 H). 13C NMR (100 MHz, CDCl3):
d = 198.18, 158.27, 140.18, 133.32, 129.95, 128.78, 128.31,
40.80, 37.91, 37.56, 25.74, 23.94, 23.81, 22.43, 18.85,
18.70, 13.94. HRMS: m/z calcd for C19H24ONa+: 291.3824;
found: 291.3830.
Compound 7i: IR (NaCl): 3051, 2905, 2322, 1745, 1678,
1487, 1145 cm–1. 1H NMR (400 MHz, CDCl3): d = 8.04–
8.02 (m, 2 H), 7.39–7.37 (m, 3 H), 3.46 (q, J = 3.6 Hz, 1 H),
3.41 (q, J = 3.6 Hz, 1 H), 2.69–2.64 (m, 1 H), 1.86–1.77 (m,
5 H), 1.74–1.68 (m, 2 H), 1.66–1.59 (m, 1 H), 1.50–1.41 (m,
3 H), 1.34–1.21 (m, 5 H). 13C NMR (100 MHz, CDCl3): d =
201.37, 155.99, 136.40, 132.64, 130.11, 128.85, 128.30,
47.53, 43.66, 43.56, 29.13, 28.13, 26.62, 26.19, 25.97,
25.87, 25.57, 23.18. HRMS: m/z calcd for C20H24ONa+:
303.3932; found: 303.3930.
Compound 7j: IR (NaCl): 3067, 3032, 2863, 2246, 1769,
1649, 1652, 1507, 1338 cm–1. 1H NMR (400 MHz, CDCl3):
d = 8.05–8.03 (m, 2 H), 7.43–7.41 (m, 3 H), 7.37–7.35 (m, 1
H), 7.23–7.15 (m, 2 H), 7.11–7.09 (m, 1 H), 4.21 (d, J = 4.8
Hz, 1 H), 3.79 (t, J = 4.8 Hz, 1 H), 2.61–2.49 (m, 2 H), 2.37–
2.30 (m, 2 H), 1.65–1.50 (m, 2 H), 1.46–1.35 (m, 2 H), 1.30–
1.21 (m, 2 H), 0.84 (t, J = 7.2 Hz, 3 H). 13C NMR (100 MHz,
CDCl3): d = 197.73, 155.56, 139.72, 137.17, 136.27, 132.32,
130.51, 130.02, 129.29, 129.00, 128.91, 128.80, 128.69,
128.60, 126.58, 126.39, 43.16, 41.42, 39.84, 26.48, 25.67,
39.84, 26.48, 25.67, 25.41, 22.53, 14.12. HRMS: m/z calcd
for C23H24ONa+: 339.4253; found: 339.4254.
Compound 7k: IR (NaCl): 3065, 2949, 2845, 2358, 2249,
1728, 1634, 1598, 1579, 1501, 1446, 1289 cm–1. 1H NMR
(400 MHz, CDCl3): d = 8.05 (s, 4 H), 3.46 (q, J = 3.2 Hz, 2
H), 3.40 (q, J = 4 Hz, 2 H), 2.66–2.46 (m, 4 H), 1.80 (td,
J = 13.6, 5.2 Hz, 4 H), 1.72–1.57 (m, 8 H), 1.47–1.30 (m, 8
H), 0.92 (t, J = 7.2 Hz). 13C NMR (100 MHz, CDCl3): d =
197.79, 154.25, 137.53, 133.82, 128.86, 43.68, 43.54, 40.47,
29.68, 26.35, 25.81, 23.16, 22.43, 13.98. HRMS: m/z calcd
for C30H38O2Na+: 453.6107; found: 453.6104.
Compound 7d: IR (NaCl): 3066, 2956, 2933, 2869, 2350,
1716, 1655, 1540, 1458 cm–1. 1H NMR (400 MHz, CDCl3):
d = 8.06–8.04 (m, 2 H), 7.40–7.37 (m, 3 H), 3.47–3.38 (m, 2
H), 2.64–2.46 (m, 2 H), 1.84–1.77 (m, 2 H), 1.74–1.56 (m, 5
H), 1.49–1.33 (m, 5 H), 0.92 (t, J = 7.2 Hz, 3 H). 13C NMR
(100 MHz, CDCl3): d = 197.87, 155.07, 136.52, 132.57,
130.15, 128.92, 128.32, 43.70, 43.34, 40.41, 26.32, 26.09,
25.80, 23.17, 22.43, 13.96. HRMS: m/z calcd for
C18H22ONa+: 277.3559; found: 277.3554.
Compound 7e: IR (NaCl): 3058, 2942, 2859, 2252, 1747,
1636, 1578, 1445, 1334 cm–1. 1H NMR (400 MHz, CDCl3):
d = 7.96 (d, J = 8 Hz, 1 H), 7.74–7.69 (m, 2 H), 7.57 (d,
J = 7.2 Hz, 2 H), 7.39–7.28 (m, 4 H), 6.93 (t, J = 7.6 Hz, 2
H), 3.86 (q, J = 3.6 Hz, 1 H), 3.68 (q, J = 3.6 Hz, 1 H), 2.31–
2.27 (m, 1 H), 1.89–1.65 (m, 2 H), 1.86–1.77 (m, 2 H), 1.63–
1.51 (m, 2 H), 1.44–1.34 (m, 2 H). 13C NMR (100 MHz,
CDCl3): d = 191.50, 154.83, 139.20, 137.60, 133.31, 131.96,
131.86, 130.83, 129.02, 128.95, 128.68, 128.20, 127.60,
127.01, 126.24, 125.79, 125.23, 124.89, 48.74, 45.71, 26.85,
25.58, 23.54. HRMS: m/z calcd for C24H20ONa+: 347.4042;
found: 347.4042.
Compound 7f: IR (NaCl): 3056, 2956, 2930, 2858, 1655,
1506, 1460, 1391, 1198, 1026 cm–1. 1H NMR (400 MHz,
CDCl3): d = 7.97–7.84 (m, 3 H), 7.52–7.37 (m, 4 H), 3.62–
3.50 (m, 2 H), 2.23–2.08 (m, 2 H), 2.04–2.01 (m, 1 H), 1.84–
1.76 (m, 2 H), 1.61–1.58 (m, 2 H), 1.51–1.41 (m, 1 H), 1.38–
1.26 (m, 4 H), 0.59 (t, J = 7.6 Hz, 3 H). 13C NMR (100 MHz,
CDCl3): d = 198.22, 155.35, 141.22, 133.55, 132.77, 130.74,
128.86, 128.51, 126.48, 126.20, 125.81, 125.41, 125.13,
48.87, 43.80, 39.96, 26.37, 26.23, 24.96, 23.47, 22.16,
13.52. HRMS: m/z calcd for C22H24ONa+: 327.4146; found:
327.4145.
Compound 7g: IR (NaCl): 3032, 2936, 2863, 2246, 1769,
1649, 1507, 1338 cm–1. 1H NMR (400 MHz, CDCl3): d =
7.89–7.86 (m, 2 H), 7.54–7.47 (m, 3 H), 7.39–7.35 (m, 2 H),
7.26–7.24 (m, 1 H), 3.41–3.30 (m, 2 H), 2.06–1.96 (m, 1 H),
1.87–1.47 (m, 7 H). 13C NMR (100 MHz, CDCl3): d =
191.65, 157.03, 139.83, 138.07, 133.36, 132.40, 129.37,
128.86, 128.53, 128.41, 128.22, 39.68, 38.60, 24.10, 23.51,
18.82, 18.70. HRMS: m/z calcd for C21H20ONa+: 311.3721;
found: 311.3725.
Compound 7h: IR (NaCl): 2961, 2860, 2255, 1794, 1714
cm–1. 1H NMR (400 MHz, CDCl3): d = 8.01–7.98 (m, 2 H),
7.40–7.37 (m, 3 H), 3.19 (q, J = 6.0 Hz, 1 H), 3.13 (q, J = 5.6
Hz, 1 H), 2.62–2.43 (m, 2 H), 1.97–1.89 (m, 2 H), 1.78–1.68
Compound 7l: IR (NaCl): 2955, 2859, 2357, 1746, 1667,
1588, 1504, 1457, 1177 cm–1. 1H NMR (400 MHz, CDCl3):
d = 7.87 (d, J = 7.6 Hz, 4 H), 7.52–7.36 (m, 10 H), 3.62 (q,
J = 3.2 Hz, 2 H), 3.54 (q, J = 3.6 Hz, 2 H), 1.82–1.62 (m, 8
H), 1.41–1.31 (m, 4 H). 13C NMR (100 MHz, CDCl3): d =
191.29, 137.31, 133.29, 128.90, 128.53, 128.47, 120.62,
45.92, 44.43, 26.48, 26.27, 23.27. HRMS: m/z calcd for
C34H30O2Na+: 493.5900; found: 493.5889.
Synlett 2008, No. 5, 777–781 © Thieme Stuttgart · New York

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