Defunctionalization of γ-alkylidene-α-hydroxybutenolides by palladium(0)-catalyzed reaction of enol triflates with hexylboronic acid

Article abstract of DOI:10.1002/ejoc.200500723

The Suzuki reaction of hexylboronic acid with enol triflates derived from γ-alkylidene-α-hydroxybutenolides resulted in reductive formation of α-unsubstituted γ-alkylidenebutenolides. The formation of the products can be explained based on an "oxidative a

Full text of DOI:10.1002/ejoc.200500723

FULL PAPER
DOI: 10.1002/ejoc.200500723
Defunctionalization of γ-Alkylidene-α-hydroxybutenolides by Palladium(0)-
Catalyzed Reaction of Enol Triflates with Hexylboronic Acid
Zafar Ahmed[a,b] and Peter Langer*[a,b]
Keywords: Butenolides / Heterocycles / Palladium
The Suzuki reaction of hexylboronic acid with enol triflates
derived from γ-alkylidene-α-hydroxybutenolides resulted in
reductive formation of α-unsubstituted γ-alkylidenebutenol-
ides. The formation of the products can be explained based
on an “oxidative addition/transmetalation/β-hydride elimi-
nation/reductive elimination” mechanism.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2006)
γ-Alkylidenebutenolides are present in a variety of phar-
macologically relevant natural products and natural prod-
uct analogues.[1] A number of natural products, such as pip-
erolide, contain a hydrogen atom located at the α-position
and a methoxy group located at the β-position of the buten-
olide.[2] γ-Alkylidene-α-hydroxybutenolides are available by
cyclization of 1,3-bis(silyl enol ethers)[3,4] with oxalyl chlo-
ride;[5] the hydroxy group has been functionalized by Stille[6]
and Suzuki[7] cross coupling reactions of the corresponding
enol triflates. This approach has been successfully applied
to the synthesis of a number of natural products, such as
pulvinic acids[8] or linderone and lucidone;[9] in addition,
an analog of norbadione A has been recently prepared.[10]
During a synthetic project, there was the need to replace
the α-hydroxy group of the butenolide by a hydrogen atom.
Brückner et al. reported Stille reactions of butenolide-de-
rived enol triflates with Bu3SnH using catalytic amounts
of palladium catalysts or NiCl2(PPh3)2.[11] However, these
conditions proved to be unsuccessful for our substrates.
Herein, we report an unexpected solution of this problem
based on the reaction of enol triflates with hexylboronic
acid; these transformations allow a convenient defunctiona-
lization of the butenolide based on an “oxidative addition/
transmetalation/β-hydride elimination/reductive elimi-
nation” mechanism.
Results and Discussion
Our starting point was the reaction of triflate 2a, readily
available from butenolide 1a,[8] with alkylboronic acids. No-
tably, the reaction of 2a with hexylboronic acid afforded the
defunctionalized γ-alkylidenebutenolide 3a rather than the
expected coupling product 4 (Scheme 1). Optimal yields
were obtained by application of standard reaction condi-
tions [3 mol-% Pd(PPh3)4, 1.5 equiv. K3PO4, dioxane, re-
flux]. All attempts to prepare 3a by palladium(0)-catalyzed
reactions using Bu3SnH or formic acid proved to be unsuc-
cessful. Unexpectedly, the use of butyl- rather than hexylbo-
ronic acid also proved to be unsuccessful.
[a] Institut für Chemie, Universität Rostock,
Albert-Einstein-Str. 3a, 18059 Rostock, Germany
Fax: +49-381-4986412
E-mail: peter.langer@uni-rostock.de
Scheme 1. Reductive cleavage of 2. i: (COCl)2, Me3SiOTf
(0.3 equiv.), CH2Cl2; ii: Tf2O, pyridine, –78 Ǟ –10 °C; iii: Pd-
(PPh3)4 (3 mol-%), K3PO4 (1.5 equiv.), dioxane, reflux.
[b] Leibniz-Institut für Organische Katalyse an der Universität Ro-
stock e. V. (IfOK),
Albert-Einstein-Str. 29a, 18059 Rostock, Germany
Eur. J. Org. Chem. 2006, 1057–1060
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1057

Z. Ahmed, P. Langer
FULL PAPER
The formation of 3a can be explained by oxidative ad- enolides 3f and 3g, containing an ethoxy and a benzyloxy
dition, transmetalation, β-hydride elimination and subse- group located at the butenolide moiety, were prepared.
quent reductive elimination (Scheme 2). It is known that Starting with 2h, the (Z)-configured butenolide 3h, contain-
alkylboranes sometimes undergo a fast β-hydride elimi- ing an acetyl rather than an alkoxycarbonyl group located
nation using Pd(PPh3)4 as a catalyst.[12]
at the exocyclic double bond, was prepared. The reaction
of hexylboronic acid with triflates 2i and 2j, containing an
ethyl group or a hydrogen atom located at the butenolide
moiety, respectively, failed to give the corresponding de-
functionalized butenolides. In contrast, the corresponding
butenolides 1i and 1j were recovered. This result can be ex-
plained based on electronic or neighbouring-group effects
exerted by the alkoxy group located at carbon atom C-4.
Notably, the reaction of hexylboronic acid with 2-methoxy-
4-(methoxycarbonyl)phenyl triflate resulted, under identical
conditions, in the formation of the expected methyl 4-hexyl-
3-methoxybenzoate (5) (Scheme 4).
Scheme 2. Possible mechanism for the formation of 3a.
Table 1. Products and yields.
The reaction of triflates 2b–d, prepared from 1b–d, with
HexB(OH)2 afforded the defunctionalized γ-alkylidenebut-
enolides 3b–d containing a methoxy-substituted butenolide
moiety and an aryl group located at the exocyclic double
bond (Scheme 3, Table 1). The high diastereomeric purity
[(E)/(Z) Ͼ 98:2] of the exocyclic double bond was not re-
duced during the reaction, due to the higher thermo-
dynamic stability of the (E)- compared to the (Z)-config-
ured isomer. Butenolide 3e was prepared by reaction of 2e
with hexylboronic acid. The high diastereomeric purity
[(E)/(Z) Ͻ 2:98] was again not reduced during the reaction,
due to the steric effect of the methoxy group and the ab-
sence of an additional substituent located at the exocyclic
double bond. Likewise, the (Z)-configured γ-alkylidenebut-
2,3
R1
R2
R3
2 [%][a]
3 [%][a] (E)/(Z)[b]
a
b
c
d
e
f
g
h
i
OMe
OMe
OMe
Ph
OMe
OMe
OMe
61[c]
77[c]
66[c]
74[c]
61[d]
89
83[d]
46
76[e]
52[e]
60
55
54
47
70
62
45
67
0
Ͼ 98:2
Ͼ 98:2
Ͼ 98:2
Ͼ 98:2
Ͻ 2:98
Ͻ 2:98
Ͻ 2:98
Ͻ 2:98
Ͻ 2:98
Ͼ 98:2
4-(MeO)C6H4
3,4-(MeO)2C6H3
OMe 3,4,5-(MeO)3C6H2 OMe
OMe
OEt
OBn
OMe
Et
H
H
H
H
H
H
OMe
OEt
OEt
Me
OEt
OMe
j
H
0
[a] Yields of isolated products. [b] Configuration of the exocyclic
double bond (by 1H NMR). [c] Known compound.[8] [d] Known
compound.[6] [e] Known compound.[7]
Scheme 4. i: nHexB(OH)2, Pd(PPh3)4 (3 mol-%), K3PO4
(1.5 equiv.), dioxane, reflux.
Conclusion
In summary, we have reported the defunctionalization of
γ-alkylidene-α-hydroxybutenolides based on palladium(0)-
catalyzed reactions of enol triflates with hexylboronic acid.
Experimental Section
General Comments: All solvents were dried by standard methods
1
and all reactions were carried out under an inert gas. For the H
and 13C NMR spectra the deuterated solvents indicated were used.
MS data were obtained using the electron ionization (70 eV) or
the chemical ionization technique (CI; H2O). For preparative-scale
chromatography silica gel (60–200 mesh) was used. Melting points
are uncorrected.
Scheme 3. Reductive cleavage of 2. i: Tf2O, pyridine, –78 Ǟ –10 °C;
ii: Pd(PPh3)4 (3 mol-%), K3PO4 (1.5 equiv.), dioxane, reflux.
1058
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© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2006, 1057–1060

Defunctionalization of γ-Alkylidene-α-hydroxybutenolides
FULL PAPER
General Procedure for the Preparation of Triflates 2: To a dichloro-
methane (10 mL per 1 mmol of starting material) solution of but-
enolide 1 (1.0 equiv.) triflic anhydride (1.2 equiv.) and pyridine
(2.0 equiv.) were added at –78 °C. The solution was warmed to
–10 °C within 4 h. The product was isolated by rapid chromatog-
raphy (silica gel; dichloromethane) of the reaction mixture.
(C), 130.91 (2 C, CH), 139.59, 160.53, 166.88, 167.50, 170.01 (C)
ppm. IR (KBr): ν = 3215 (w), 2926 (w), 1779 (s), 1732 (s), 1605
˜
(s), 1514 (m), 1289 (m), 1258 (m), 1185 (m), 1043 (m), 873 (m)
cm–1. MS (EI; 70 eV): m/z (%) = 290.0 (100) [M+], 231.0 (81), 175.0
(19), 147.4 (19), 83.1 (44). C15H14O6 (290.27): calcd. C 62.06, H
4.86; found C 61.80, H 5.03.
2f: Starting with 1f (311 mg, 1.36 mmol), pyridine (0.22 mL,
2.72 mmol) and triflic anhydride (0.27 mL, 1.63 mmol), 2f was iso-
lated as a yellow solid (433 mg, 89%), m.p. 60–62 °C. 1H NMR
(300 MHz, CDCl3): δ = 1.33 (t, 3 H, J = 7.2 Hz, CH3), 1.51 (t, 3
H, J = 6.9 Hz, CH3), 4.28 (q, 2 H, J = 7.2 Hz, OCH2), 4.61 (q, 2
H, J = 6.9 Hz, OCH2), 5.83 (s, 1 H, =CH) ppm. 13C NMR
(75 MHz, CDCl3): δ = 14.09, 14.88 (CH3), 61.43, 70.14 (CH2),
3c: Starting with 2c (196 mg, 0.41 mmol), hexylboronic acid
(71 mg, 0.54 mmol), K3PO4 (142 mg, 0.66 mmol) and Pd(PPh3)4
(15 mg, 0.01 mmol), 3c was isolated as a yellow solid (71 mg, 54%),
m.p. 155–156 °C. 1H NMR (300 MHz, CDCl3): δ = 3.88 (s, 3 H,
OCH3), 3.90 (s, 6 H, OCH3), 3.96 (s, 3 H, OCH3), 5.34 (s, 1 H,
=CH), 6.87 (d, 1 H, J = 8.5 Hz, ArH), 7.16 (dd, 1 H, J = 2.2 Hz,
8.5 Hz, ArH), 7.30 (d, 1 H, J = 2.1 Hz, ArH) ppm. 13C NMR
100.41 (CH), 113.85 (C), 118.30 (q, J = 319.5, CF3), 148.23, 154.41, (75 MHz, CDCl3): δ = 52.76, 55.86, 55.93, 59.99 (CH3), 89.69,
159.89, 162.16 (C) ppm. IR (KBr): ν = 2990 (s), 1813 (s), 1722 (s), 110.95, 112.09 (CH), 116.33 (C), 122.61 (CH), 123.34, 139.66,
˜
1664 (s), 1430 (s), 1328 (s), 1236 (s), 1133 (m), 1032 (m), 944 (m), 148.88, 150.24, 166.69, 167.26, 169.90 (C) ppm. IR (KBr): ν = 3115
˜
814 (m) cm–1. MS (EI; 70 eV): m/z (%) = 359.9 (2) [M+], 314.9 (2), (w), 2948 (w), 1769 (s), 1733 (s), 1604 (s), 1522 (s), 1448 (m), 1366
198.9 (33), 114.3 (49), 69.9 (100). C11H11O8SF3 (360.26): calcd. C (m), 1262 (s), 1155 (m), 873 (m) cm–1. MS (EI; 70 eV): m/z (%) =
36.67, H 3.07; found C 36.77, H 3.48.
320.0 (100) [M+], 261.1 (76), 205.1 (14), 143.1 (9), 69.9 (17).
C16H16O7 (320.29): calcd. C 59.99, H 5.03; found C 59.66, H 5.28.
2h: Starting with 1h (700 mg, 3.80 mmol), pyridine (0.61 mL,
7.60 mmol) and triflic anhydride (0.77 mL, 4.56 mmol), 2h was iso-
lated as a yellow solid (550 mg, 46%), m.p. 51–52 °C. 1H NMR
(300 MHz, CDCl3): δ = 2.51 (s, 3 H, CH3), 4.33 (s, 3 H, OCH3),
3d: Starting with 2d (245 mg, 0.49 mmol), hexylboronic acid
(83 mg, 0.64 mmol), K3PO4 (256 mg, 0.78 mmol) and Pd(PPh3)4
(18 mg, 0.014 mmol), 3d was isolated as a yellow solid (80 mg,
5.90 (s, 1 H, =CH) ppm. 13C NMR (75 MHz, CDCl3): δ = 31.83, 47%), m.p. 149–150 °C. H NMR (300 MHz, CDCl3): δ = 3.87 (s,
1
60.70 (CH3), 108.46 (CH), 113.66 (C), 118.40 (q, J = 319.50 Hz, 12 H, OCH3), 3.97 (s, 3 H, OCH3), 5.37 (s, 1 H, =CH), 6.87 (s, 2
CF ), 146.75, 155.71, 159.32, 194.80 (C) ppm. IR (KBr): ν = 1804
H, ArH) ppm. 13C NMR (75 MHz, CDCl3): δ = 52.82, 56.21 (2
˜
3
(s), 1674 (s), 1428 (s), 1362 (m), 1325 (m), 1237 (s), 1217 (s), 1135
C), 60.05, 60.84 (CH3), 90.09, 106.62 (2 C, CH), 116.17, 125.86,
(s), 1073 (s), 956 (m), 828 (m) cm–1. MS (EI; 70 eV): m/z (%) = 139.39, 140.59, 153.13 (2 C), 166.45, 167.01, 169.75 (C) ppm. IR
316.6 (7) [M+], 300.6 (21), 167.8 (27), 126.9 (48), 69.9 (61).
C9H7O7SF3 (316.21): calcd. C 34.18, H 2.23; found C 34.51, H
2.44.
(KBr): ν = 2943 (w), 1778 (s), 1740 (s), 1607 (s), 1510 (m), 1336
˜
(m), 1275 (m), 1249 (m), 1160 (m), 1127 (s), 1057 (m), 866 (m)
cm–1. MS (EI; 70 eV): m/z (%) = 349.7 (3) [M+], 290.7 (3), 238.8 (3),
180.9 (5), 57.3 (7), 28.0 (100). C17H18O8 (350.32): calcd. C 58.28, H
5.17; found C 58.68, H 5.10.
General Procedure for the Synthesis of Butenolides 3 by Suzuki Re-
actions: A dioxane (5 mL per 1 mmol of starting material) solution
of triflate 2 (1.0 equiv.), hexylboronic acid (1.3 equiv.), K3PO4
(1.5 equiv.) and Pd(PPh3)4 (3 mol-%) was refluxed for 4 h. A satu-
rated aqueous solution (10 mL) of ammonium chloride was added.
The organic and the aqueous layer were separated and the latter
was extracted (3×) with diethyl ether. The combined organic layers
were dried (Na2SO4), filtered and the filtrate was concentrated in
vacuo. The residue was purified by chromatography (silica gel;
EtOAc/hexane).
3e: Starting with 2e (400 mg, 1.20 mmol), hexylboronic acid
(203 mg, 1.56 mmol), K3PO4 (383 mg, 1.80 mmol) and Pd(PPh3)4
(42 mg, 0.03 mmol), 3e was isolated as a yellow solid (154 mg,
1
70%), m.p. 120–121 °C. H NMR (300 MHz, CDCl3): δ = 3.81 (s,
3 H, OCH3), 3.98 (s, 3 H, OCH3), 5.38 (s, 1 H, =CH), 5.64 (s, 1
H, =CH) ppm. 13C NMR (75 MHz, CDCl3): δ = 53.01, 59.69
(CH3), 90.96, 95.98 (CH), 151.60, 163.61, 166.68, 170.16 (C) ppm.
IR (KBr): ν = 3395 (w), 3224 (m), 3133 (m), 1796 (s), 1729 (s),
˜
1674 (m), 1625 (s), 1440 (m), 1353 (m), 1238 (m), 1149 (m), 853
(m), 745 (w) cm–1. MS (EI; 70 eV): m/z (%) = 183.9 (28) [M+], 152.4
(41), 125.0 (8), 69.9 (100). C8H8O5 (184.14): calcd. C 52.18, H 4.37;
found C 52.22, H 4.50.
3a: Starting with 2a (100 mg, 0.24 mmol), hexylboronic acid
(42 mg, 0.31 mmol), K3PO4 (84 mg, 0.39 mmol) and Pd(PPh3)4
(10 mg, 0.008 mmol), 3a was isolated as a yellow solid (38 mg,
1
60%), m.p. 137–138 °C. H NMR (300 MHz, CDCl3): δ = 3.88 (s,
3 H, OCH3), 3.97 (s, 3 H, OCH3), 5.37 (s, 1 H, =CH), 7.26–7.66 3f: Starting with 2f (360 mg, 0.99 mmol), hexylboronic acid
(m, 5 H, ArH) ppm. 13C NMR (150 MHz, CDCl3): δ = 53.02, 60.27
(169 mg, 1.30 mmol), K3PO4 (340 mg, 1.60 mmol) and Pd(PPh3)4
(CH3), 90.50 (CH), 116.62 (C), 128.94 (2 C), 129.31 (2 C), 129.68
(35 mg, 0.03 mmol), 3f was isolated as a yellow solid (130 mg,
1
(CH), 130.96, 141.22, 166.76, 167.40, 170.09 (C) ppm. IR (KBr): ν 62%), m.p. 129–130 °C. H NMR (300 MHz, CDCl3): δ = 1.32 (t,
˜
= 3433 (w), 2954 (w), 1766 (s), 1730 (s), 1607 (s), 1440 (m), 1366 3 H, J = 7.2 Hz, CH3), 1.47 (t, 3 H, J = 6.9 Hz, CH3), 4.18 (q, 2
(m), 1300 (m), 1207 (m), 1043 (m), 974 (m), 872 (m), 793 (m) cm–1. H, J = 6.9 Hz, OCH2), 4.26 (q, 2 H, J = 7.2 Hz, OCH2), 5.33 (s, 1
MS (EI; 70 eV): m/z (%) = 260.1 (77) [M+], 201.0 (12), 144.8 (26), H, =CH), 5.66 (s, 1 H, =CH) ppm. 13C NMR (75 MHz, CDCl3):
118.0 (49), 69.9 (59). C14H12O5 (260.24): calcd. C 64.61, H 4.64;
found C 64.10, H 4.85.
δ = 13.89, 14.11 (CH3), 60.96, 69.07 (CH2), 90.80, 96.24 (CH),
151.80, 163.21, 167.10, 169.16 (C) ppm. IR (KBr): ν = 3423 (w),
˜
3123 (m), 1807 (s), 1723 (s), 1676 (s), 1620 (s), 1332 (s), 1238 (s),
1148 (s), 1025 (m), 835 (m) cm–1. MS (EI; 70 eV): m/z (%) = 211.8
(7) [M+], 183.8 (21), 166.8 (27), 138.9 (19), 86.8 (26). C10H12O5
(212.20): calcd. C 56.60, H 5.70; found C 56.70, H 5.84.
3b: Starting with 2b (100 mg, 0.22 mmol), hexylboronic acid
(39 mg, 0.29 mmol), K3PO4 (112 mg, 0.34 mmol) and Pd(PPh3)4
(8 mg, 0.006 mmol), 3b was isolated as a yellow solid (35 mg, 55%),
m.p. 141–142 °C. 1H NMR (300 MHz, CDCl3): δ = 3.83 (s, 3 H,
OCH3), 3.88 (s, 3 H, OCH3), 3.95 (s, 3 H, OCH3), 5.33 (s, 1 H, 3g: Starting with 2g (200 mg, 0.51 mmol), hexylboronic acid
=CH), 6.92 (dd, 2 H, J = 2.1, 6.9 Hz, ArH), 7.61 (dd, 2 H, J =
2.1 Hz, 6.9 Hz, ArH) ppm. 13C NMR (75 MHz, CDCl3): δ = 52.83,
55.38, 60.02 (CH3), 89.73 (CH), 114.31 (2 C, CH), 116.40, 123.21
(86 mg, 0.66 mmol), K3PO4 (174 mg, 0.81 mmol) and Pd(PPh3)4
(20 mg, 0.01 mmol), 3g was isolated as a yellow solid (63 mg, 45%),
1
m.p. 120–121 °C. H NMR (300 MHz, CDCl3): δ = 1.31 (t, 3 H, J
Eur. J. Org. Chem. 2006, 1057–1060
© 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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1059

Z. Ahmed, P. Langer
FULL PAPER
= 6.9 Hz, CH3), 4.26 (q, 2 H, J = 6.9 Hz, OCH2), 5.14 (s, 2 H,
OCH2), 5.41 (s, 1 H, =CH), 5.69 (s, 1 H, =CH), 7.35–7.44 (m, 5
H, ArH) ppm. 13C NMR (75 MHz, CDCl3): δ = 14.12 (CH3),
61.03, 74.69 (CH2), 91.91, 96.56, 127.91 (2 C), 128.93 (2 C), 129.30
Acknowledgments
Financial support from the Deutsche Forschungsgemeinschaft and
from the state of Mecklenburg-Vorpommern (scholarship for Z. A.)
is gratefully acknowledged.
(CH), 133.19, 151.70, 163.16, 166.89, 168.75 (C) ppm. IR (KBr): ν
˜
= 3425 (m), 3102 (w), 1794 (s), 1701 (s), 1615 (s), 1324 (m), 1285
(m), 949 (m), 855 (m) cm–1. MS (EI; 70 eV): m/z (%) = 274.1 (5)
[M+], 246.0 (6), 229.0 (4), 205.0 (4), 159.0 (7), 91.0 (100). C15H14O5
(274.27): calcd. C 65.68, H 5.14; found C 65.41, H 5.41.
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3h: Starting with 2h (320 mg, 1.01 mmol), hexylboronic acid
(170 mg, 1.30 mmol), K3PO4 (343 mg, 1.61 mmol) and Pd(PPh3)4
(35 mg, 0.03 mmol), 3h was isolated as a yellow solid (114 mg,
1
67%), m.p. 112–114 °C. H NMR (300 MHz, CDCl3): δ = 2.52 (s,
3 H, CH3), 4.01 (s, 3 H, OCH3), 5.42 (s, 1 H, =CH), 5.73 (s, 1 H,
=CH) ppm. 13C NMR (75 MHz, CDCl3): δ = 31.09, 59.76 (CH3),
90.69, 104.90 (CH), 150.35, 166.26, 170.85, 196.13 (C) ppm. IR
(KBr): ν = 3105 (m), 1797 (s), 1769 (m), 1657 (s), 1616 (s), 1359
˜
(m), 1332 (m), 1257 (s), 1182 (m), 976 (s), 849 (s) cm–1. MS (EI;
70 eV): m/z (%) = 167.8 (17) [M+], 152.3 (47), 136.8 (34), 110.0
(10), 69.8 (100). C8H8O4 (168.14): calcd. C 57.14, H 4.79; found C
57.48, H 5.36.
5: Starting with triflate (315 mg, 1.00 mmol), hexylboronic acid
(169 mg, 1.30 mmol), K3PO4 (340 mg, 1.60 mmol) and Pd(PPh3)4
(35 mg, 0.03 mmol), 5 was isolated as a colorless oil (100 mg, 40%).
1H NMR (250 MHz, CDCl3): δ = 0.87 (t, 3 H, J = 1.5 Hz, CH3),
1.29–1.60 (m, 8 H, CH2), 2.63 (t, 2 H, J = 7.6 Hz, CH2), 3.86 (s,3
H, OCH3), 3.89 (s,3 H, OCH3), 7.16 (d, 1 H, J = 7.6 Hz, ArH),
7.49 (d, 1 H, J = 1.5 Hz, ArH), 7.57 (dd, 1 H, J = 1.8 Hz, 7.6 Hz,
ArH) ppm. 13C NMR (75 MHz, CDCl3): δ = 14.11 (CH3), 22.65,
29.24, 29.47, 30.31, 31.97 (CH2), 52.00, 55.42 (CH3), 111.09, 122.18
(CH), 129.38 (C), 129.54 (CH), 137.13, 157.32, 167.23 (C) ppm. IR
[10] M. Desage-El Murr, S. Nowaczyk, T. Le Gall, C. Mioskowski,
B. Amekraz, C. Moulin, Angew. Chem. 2003, 115, 1327; Angew.
Chem. Int. Ed. 2003, 42, 1289.
[11] a) K. Siegel, R. Brückner, Chem. Eur. J. 1998, 4, 1116; b) F.
Goerth, A. Umland, R. Brückner, Eur. J. Org. Chem. 1998,
1055.
(neat): ν = 3054 (m), 2928 (m), 2858 (m), 1722 (s), 1460 (m), 1291
˜
(m), 1106 (w), 761 (w) cm–1. MS (EI; 70 eV): m/z (%) = 249.8 (50)
[M+], 218.8 (8), 178.8 (100), 148.1 (17), 120.8 (14). C15H22O3
(250.33): calcd. C 71.97, H 8.86; found C 72.03, H 9.07.
[12] N. Miyaura, A. Suzuki, Chem. Rev. 1995, 95, 2457.
Received: September 23, 2005
Published Online: December 12, 2005
1060
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Eur. J. Org. Chem. 2006, 1057–1060