Catalytic deprotonative functionalization of propargyl silyl ethers with imines

Article abstract of DOI:10.1002/adsc.200800281

A metal-free, catalytic C-H functionalization of propargyl silyl ethers with imines using the phosphazene base (t-Bu-P₄ base) provides structurally defined multisubstituted pyrroles in modest to excellent yields under mild conditions. A one-pot, three-component reaction using silylated acetylenes, aldehydes, and imines is also presented.

Full text of DOI:10.1002/adsc.200800281

FULL PAPERS
DOI: 10.1002/adsc.200800281
Catalytic Deprotonative Functionalization of Propargyl Silyl
Ethers with Imines
Hiroshi Naka,a,* Daiki Koseki,a and Yoshinori Kondoa,*
a
Graduate School of Pharmaceutical Sciences, Tohoku University, Aobayama, Aoba-ku, Sendai 980-8578, Japan
Fax : (+81)-22-795-5917; e-mail: naka@mail.pharm.tohoku.ac.jp or ykondo@mail.pharm.tohoku.ac.jp
Received: May 7, 2008; Revised: June 9, 2008; Published online: July 24, 2008
Supporting information for this article is available on the WWW under http://asc.wiley-vch.de/home/.
ꢀ
Abstract: A metal-free, catalytic C H functionaliza- three-component reaction using silylated acetylenes,
tion of propargyl silyl ethers with imines using the aldehydes, and imines is also presented.
phosphazene base (t-Bu-P4 base) provides structural-
ly defined multisubstituted pyrroles in modest to ex- Keywords: anionic reactions; C C bond formation;
cellent yields under mild conditions. A one-pot, heterocycles; metal-free conditions; phosphazene
bases
ꢀ
Introduction
Results and Discussion
ꢀ
ꢀ
ꢀ
Direct C C bond-forming reactions through propar- As a part of our survey on nucleophilic C H and C
gylic C H deprotonation are among the most power- Si functionalization using catalytic t-Bu-P4 base,[5,6] we
ꢀ
ful methods in modern organic synthesis, since they found that reaction of propargyl silyl ether 1a with
provide variously substituted allenes or propargylic imine 2a in the presence of 10 mol% of t-Bu-P4 base
compounds that serve as versatile building blocks in provides a tetraphenylated pyrrole 3aa in 94% yield
many synthetic scenarios.[1–3] Traditionally, strong or- (Table 1, entry 1).[7]
ganometallic bases such as organolithium reagents
Because the pyrrole ring architecture is one of the
have been used for such deprotonations.[1,2] However, most ubiquitous functionalities found in natural prod-
reactions using these reactive reagents often suffer ucts, bioactive chemicals, and functional molecules,[8,9]
from undesirable side reactions such as addition to we expected that the present catalysis would be a
electrophilic functional groups, and halogen-metal ex- powerful tool for the facile synthesis of multisubstitut-
change reactions to organic halide functionalities. Fur- ed pyrroles using propargyl silyl ethers 1 and imines
thermore, these reactions require stoichiometric use 2, both of which are easily prepared from aldehydes
of the organometallic reagents, and need to be carried and alkynes, and from aldehydes and amines respec-
out at very low temperatures (ꢀ788C to ꢀ1008C), tively. Thus, the reaction of 1a with various imines
both of which are undesirable for large-scale applica- 2a–n using t-Bu-P4 base was examined (Table 1). The
tions. Thus, a chemoselective, catalytic direct func- reaction can be performed using 5 mol% of t-Bu-P4
tionalization of propargylic compounds under mild base to give pyrrole 3aa in 92% yield (entry 2). Func-
conditions remains an attractive challenge.
tional groups such as halogens (Cl, Br, and I), ester
We have recently focused on the potential applica- (COOMe), CF3, methyl, and ether (OMe) on aromat-
bility of phosphazene base (t-Bu-P4 base)[4] as a che- ic rings were tolerated to give variously substituted
moselective catalytic substitute for strong organome- pyrroles in good to excellent yields (entries 3–12; 61–
tallic bases.[5] Herein, we report the first catalytic de- 99%). The reaction of naphthyl- or heteroaromatic-
ꢀ
protonative C C bond-forming functionalization of substituted imines also proceeded efficiently to give
propargyl silyl ethers with imines. The reaction direct- the corresponding pyrroles 3al–an (entries 13–15; 71–
ly afforded a variety of highly substituted pyrroles 96%).
under mild and metal-free conditions.
Reactions of other propargyl silyl ethers 1b–h with
imines were similarly carried out (Table 2). Formation
of 3ba–da was observed in the reaction of 1b–d with
2a (entries 1–3; 68–91%).[10] Bis-thienylated pyrrole
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Hiroshi Naka et al.
FULL PAPERS
Table 1. Phosphazene-catalyzed direct functionalization of
1a with imines 2a–n.[a]
To obtain mechanistic information, a preliminary
deuterium labeling study using 1-[D]-1a was conduct-
ed. It was found that hydrogen at the 4-position on
the pyrrole 3aa originates exclusively from the prop-
argylic hydrogen in the silyl ether, and that the elimi-
nated Me3SiOH does not act as a proton source [Eq.
(2)].
A cross-over experiment using a mixture of 1-[D]-
1a and 1-[H]-1d gave a mixture of partially deuterated
pyrroles (4-[H]-3aa:4-[D]-3aa=35:65, 4-[H]-3da:4-
[D]-3da=47:53), suggesting that the intermediate
anions do not form strong ion pairs with the phospha-
zenium cations.[11] With these observations in hand, a
mechanistic hypothesis involving t-Bu-P4 base-mediat-
ed deprotonation of 1 at the propargylic position was
developed (Scheme 1). We consider that the inter-
mediate siloxylallenyl anion A reacts with imine 2
through a phosphazenium-activated imine B to form
allenylated intermediate C. Protonative ring closure
with another 1 gives the cyclized intermediate D and
siloxyallenyl anion A. The elimination of SiMe3OH
from D yields the pyrrole 3.
Entry
R1, R2 (Imine)
Product
Yield [%][b]
1
Ph, Ph (2a)
Ph, Ph (2a)
3aa
3aa
3ab
3ac
3ad
3ae
3af
3ag
3ah
3ai
3aj
3ak
3al
3am
3an
94
92
97
84
74
74
99
93
86
83
61
85
96
71
84
2[c]
3
p-C6H4Cl, Ph (2b)
p-C6H4Br, Ph (2c)
p-C6H4I, Ph (2d)
p-C6H4OMe, Ph (2e)
Ph, p-C6H4Cl (2f)
Ph, p-C6H4Br (2g)
Ph, p-C6H4COOMe (2h)
Ph, p-C6H4CF3 (2i)
Ph, p-C6H4Me (2j)
Ph, p-C6H4OMe (2k)
Ph, 2-naphthyl (2l)
Ph, 2-furyl (2m)
4
5
6
7
8
9
10
11
12
13
14
15
Ph, 2-thienyl (2n)
[a]
The reactions were carried out using 1a (0.375 mmol.), 2
(0.25 mmol), t-Bu-P4 base (10 mol%) in hexane (25 mL),
and toluene (1.0 mL).
Isolated yield.
5 mol% of t-Bu-P4 base were used.
Conclusions
ꢀ
In summary, we found a novel direct C C bond-form-
[b]
[c]
ing functionalization of propargyl silyl ethers with
imines catalyzed by t-Bu-P4 base, providing multi-sub-
stituted pyrroles in good to excellent yields under
3en and alkenyl-substituted pyrrole 3fa were also suc- metal-free mild conditions. The present method pro-
cessfully prepared in 80% and 73% yield, respectively vides a convenient entry for the facile synthesis of
(entries 4 and 5). Although the reaction of 1-alkyl- variously functionalized pyrroles using easily accessi-
substituted silyl ether 1g did not proceed at all ble starting materials. Further studies to elucidate in
(entry 6), the 3-alkyl-substituted silyl ether 1h fur- detail the reaction mechanism, as well as the scope
nished the product 3ha in 23% yield (entry 7). Assem- and limitations of this catalytic direct generation-func-
bly of various aromatic rings was easily accomplished, tionalization of siloxyallenyl anions, are in progress.
giving a multifunctionalized pyrrole 3ch in 77% yield
(entry 8).
Moreover, the one-pot, three-component reaction
of alkynylsilane 4, aldehyde 5, and imine 2f was car-
Experimental Section
ꢀ
ried out using t-Bu-P4 base as a dual catalyst for Si C
and C H functionalization [Eq. (1)]. The reaction
[6]
General Comments
ꢀ
was found to proceed smoothly to give the corre-
Reactions were carried out under an argon atmosphere
using dry solvents. Melting points (mp) were determined
sponding pyrrole 3df in 84% yield.
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Catalytic Deprotonative Functionalization of Propargyl Silyl Ethers
FULL PAPERS
Table 2. Phosphazene-catalyzed direct functionalization of propargyl silyl ether with imines.[a]
Entry
Silyl ether
Imine
Product, Yield[b]
1
2
3
1b: R=Cl
1c: R=Br
1d: R=OMe
2a
2a
2a
3ba: R=Cl, 91%
3ca: R=Br, 76%
3da: R=OMe, 68%
4
1e
1f
1g
1h
1c
2n
2a
2a
2a
2h
3en, 80%
3fa, 73%
3ga, 0%
5[c]
6
7
3ha, 23%
3ch, 77%
8
[a]
The reactions were carried out using 1a (0.375 mmol.), 5 (0.25 mmol), t-Bu-P4 base (10 mol%) in hexane (25 mL), and tol-
uene (1.0 mL) at room temperature for 3 h.
Isolated yield.
Reaction performed at ꢀ408C.
[b]
[c]
Scheme 1. A plausible mechanism for the phosphazene-catalyzed direct functionalization of propargyl silyl ether 1 with
imine 2.
with a Yazawa micro melting point apparatus and are uncor-
rected. Infrared (IR) data were recorded on a SensIR ATR
(Attenuated Total Reflectance) FT-IR spectrometer. The
spectra were acquired in 32 scans per spectrum at a resolu-
tion of four using system ReactIRꢁ 2.20 software. Absorb-
ance frequencies are reported in reciprocal centimeters
(cmꢀ1). NMR data were recorded on a JEOL AL400 spec-
1
trometer (395.75 MHz for H, 99.50 MHz for 13C). Chemical
shifts are expressed in d (parts per million, ppm) values, and
coupling constants are expressed in hertz (Hz). 1H NMR
spectra were referenced to tetramethylsilane as an internal
standard. 13C NMR spectra were referenced to a tetrame-
Adv. Synth. Catal. 2008, 350, 1901 – 1906
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Hiroshi Naka et al.
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1
thylsilane as an internal standard or to a solvent signal
(CDCl3: 77.0 ppm). The following abbreviations are used:
s=singlet, d=doublet, t=triplet, q=quartet, m=multiplet,
dd=double doublet, dt=double triplet, td=triple doublet,
dq=double quartet, br=broad singlet. Low- and high-reso-
lution mass spectra (LR-MS and HR-MS) were obtained
from the Mass Spectrometry Resource, Graduate School of
Pharmaceutical Sciences, Tohoku University, on JEOL JMS-
DX303 and JMS-700 spectrometera, respectively.
colorless needles; mp 51–528C; H NMR (400 MHz, CDCl3/
TMS): d=7.18–7.25 (m, 3H), 7.38 (t, J=8.0 Hz, 2H), 7.44–
7.48 (m, 3H), 7.87–7.92 (m, 2H), 8.44 (s, 1H); 13C{1H} NMR
(100 MHz, CDCl3): d=120.83, 125.89, 128.73, 128.77, 129.11,
131.33, 136.19, 152.05, 160.33; LR-MS (EI) m/z=181 (M+);
HR-MS: m/z=181.0883, calcd. for C13H11N: 181.0891; IR
(neat): n=3058, 2889, 2360, 1625, 1576, 1449, 1366, 1192,
1162, 754, 690 cmꢀ1.
Typical Procedure for the Synthesis of Pyrrole 3aa[12]
Materials
To a mixture of imine (0.25 mmol) and propargyl silyl ether
(0.375 mmol) in toluene (1.0 mL) was added dropwise t-Bu-
P4 base (1.0M solution in n-hexane, 25 mL, 0.025 mmol) at
room temperature under an argon atmosphere. The reaction
mixture was stirred for 3 h, then quenched with saturated
NH4Cl and extracted with AcOEt. The organic layer was
washed with brine, dried over MgSO4, and concentrated
using a rotary evaporator to afford the crude product. Pu-
rification by column chromatography on silica gel afforded
1,2,3,5-tetraphenyl-1-H-pyrrole (3aa).Recrystallization from
acetone/hexane gave colorless needles; mp 202–2048C; anal.
calcd. for C28H21N: C 90.53, H 5.70, N 3.77; found: C 90.58,
Unless otherwise noted, materials were purchased from
Tokyo Kasei Co., Aldrich Inc., and other commercial suppli-
ers and were used after appropriate purification (distillation
or recrystallization). t-Bu-P4 base (tert-butyl P4 base, 1.0M
solution in n-hexane) was purchased from Fluka Chemie
and used as supplied. Flash column chromatographies were
performed with Kanto silica gel 60 N (spherical, neutral, 70–
230 mesh).
Typical Procedure for the Preparation of Propargyl
Silyl Ether 1a
1
H 5.90, N 3.74; H NMR (400 MHz, CDCl3/TMS): d=6.70
To a solution of phenylacetylene (1.47 g, 15.0 mmol) in THF
(100 mL) was added dropwise n-BuLi (1.6M solution in n-
hexane, 9.8 mL, 15.7 mmol) at ꢀ788C under an argon at-
mosphere. The reaction mixture was stirred for 1 h, then
benzaldehyde (1.02 g, 10.0 mmol) was added at ꢀ788C. The
reaction mixture was stirred for 1 h, then quenched with sa-
turated NH4Cl and extracted with AcOEt. The organic layer
was washed with brine, dried over MgSO4, and concentrated
using a rotary evaporator to afford the crude product. Pu-
rification by column chromatography on silica gel (gradient
elution; 5–15% AcOEt in hexane) afforded 1,3-diphenyl-
prop-2-yn-1-ol. This product was used without further purifi-
cation.
To a mixture of 1,3-diphenyl-prop-2-yn-1-ol and triethyl-
amine (2.0 mL, 14 mmol) in CH2Cl2 (10 mL) was added tri-
methylsilylchloride (1.5 mL, 12.5 mmol) at 08C. The reac-
tion mixture was stirred for 1 h, then hexane added and the
mixture filtered to remove triethylammonium chloride. The
filtrate was concentrated using a rotary evaporator to afford
the crude product. Purification by distillation (4 torr, 140–
1458C) afforded trimethyl-(1,3-diphenylprop-2-ynyloxy)si-
lane (1a); yield; 2.03 g (72% in 2 steps). Pale yellow oil;
1H NMR (400 MHz, CDCl3/TMS): d=0.25 (s, 9H), 5.71 (s,
1H), 7.28–7.33 (m, 4H), 7.38 (t, J=7.6 Hz, 2H), 7.42–7.61
(m, 2H), 7.56 (d, J=7.6 Hz, 2H); 13C{1H} NMR (100 MHz,
CDCl3): d=0.34, 65.14, 85.96, 89.73, 122.84, 126.50, 127.86,
128.23, 128.34, 128.40, 131.62, 141.44; LR-MS (EI): m/z=
280 (M+). HR-MS: m/z=280.1259, calcd. for C18H20NSi:
280.1283; IR (neat): n=3062, 2956, 1490, 1250, 1061, 872,
839, 752, 717, 688 cmꢀ1.
(s, 1H), 6.95–7.27 (m, 20H); 13C{1H} NMR (100 MHz,
CDCl3): d=109.92, 123.40, 125.39, 126.26, 126.87, 127.02,
127.75, 127.87, 128.04, 128.10, 128.38, 128.49, 129.02, 131.41,
132.11, 132.59, 132.82, 134.73, 136.04, 138.72; LR-MS (EI):
m/z=371 (M+); HR-MS: m/z=371.1656, calcd. for C28H21N:
371.1674; IR (neat): n=3058, 1598, 1493, 1370, 1077, 1027,
914, 758, 694 cmꢀ1.
One-Pot Synthesis of Pyrrole 3df using Aldehyde,
Alkynylsilane and Imine
To
a
mixture of 4-methoxybenzaldehyde (102.1 mg,
0.75 mmol) and phenylethynyltrimethylsilane (139.4 mg,
0.8 mmol) in toluene (1.0 mL) was dropwised t-Bu-P4 base
(1.0M solution in n-hexane, 100 mL, 0.1 mmol) at ꢀ788C
under an argon atmosphere. The reaction mixture was
stirred for 1 h, then a solution of 4-chlorobenzylideneaniline
(107.9 mg, 0.5 mmol) in toluene (0.5 mL) was added and the
mixture warmed up to room temperature. The reaction mix-
ture was stirred for 1 h, then quenched with saturated
NH4Cl and extracted with AcOEt. The organic layer was
washed with brine, dried over MgSO4, and concentrated
using a rotary evaporator to afford the crude product. Pu-
rification by column chromatography on silica gel (gradient
elution; 20–30% toluene in hexane) afforded 2-(4-chloro-
phenyl)-5-(methoxyphenyl)-1,3-diphenyl- 1-H-pyrrole (3df);
yield: 182.4 mg (84%). Recrystallization from acetone/
hexane gave colorless needles; mp 203–2048C; anal. xalcd.
for C29H22ClNO: C 79.90, H 5.09, Cl, 8.13, N 3.21, O 3.67;
1
found: C 79.92, H 5.24, N 3.31; H NMR (400 MHz, CDCl3/
TMS): d=3.75 (s, 3H), 6.61 (s, 1H), 6.73 (d, J=8.8 Hz, 2H),
6.91–6.99 (m, 4H), 7.03 (d, J=8.8 Hz, 2H), 7.09 (d, J=
8.4 Hz, 2H), 7.13–7.26 (m, 8H); 13C{1H} NMR (100 MHz,
CDCl3): d=55.11, 109.43, 113.46, 123.78, 125.30, 125.66,
127.25, 128.12, 128.22, 128.28, 128.64, 129.09, 129.89, 130.05,
131.20, 132.59, 132.75, 135.07, 135.95, 138.61, 158.33; LR-MS
(EI): m/z=435 (M+); HR-MS: m/z=435.1391, calcd. for.
C29H22ClNO: 435.1390; IR (neat): n=3074, 2834, 2358, 1603,
Typical Procedure for the Preparation of Imine 2a
Benzaldehyde (2.65 g, 25 mmol) and aniline (2.33 g,
25 mmol) were dissolved in ethanol (30 mL). The reaction
mixture was stirred for 3 h at room temperature. The solvent
was removed using a rotary evaporator. Purification of the
residue by recrystallization gave N-benzylideneaniline (2a);
yield: 3.36 g (83%) Recrystallization from Et2O/hexane gave
1904
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ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2008, 350, 1901 – 1906

Catalytic Deprotonative Functionalization of Propargyl Silyl Ethers
FULL PAPERS
1488, 1374, 1245, 1175, 1090, 1030, 1011, 829, 798, 760,
739 cmꢀ1.
1610–1612; Angew. Chem. Int. Ed. 2002, 41, 1532–
1535; f) O. Flçgel, M. G. Okala Amombo, H.-U. Reis-
sig, G. Zahn, I, Brüdgam, H. Hartl, Chem. Eur. J.
2003, 9, 1405–1415; g) A. Chowdhury, H.-U. Reissig,
Synlett 2006, 15, 2383–2386; h) T. K. Macklin, J. Pante-
leev, V. Snieckus, Angew. Chem. 2008, 120, 2127–2131;
Angew. Chem. Int. Ed. 2008, 47, 2097–2101.
X-Ray Analysis of 3ba
5-(4-Chlorophenyl)-1,2,3-triphenyl-1-H-pyrrole 3ba was re-
crystallized from acetone/n-hexane at room temperature. X-
ray data were collected on a Rigaku RAXIS-RAPID dif-
fractometer with graphite monochromated Mo-Ka radiation
(l=0.71075 Š). The data were corrected for Lorentz and
polarization effects. The structures were solved by direct
methods and refined by full-matrix least squares against F2
using SHELXL-97 program.[13] Crystal data for the structure
of 3ba have been deposited in the Cambridge Crystalloga-
phic Data Center with number CCDC 671214. Crystal data
[3] a) J. Tsuji, in: Transition Metal Reagents and Catalysts,
John Wiley & Sons, Chichester, 2000, pp 199–226; b) S.
Ma, Pure Appl. Chem. 2006, 78, 197–208; c) S. Ma,
Chem. Rev. 2005, 105, 2829–2872; d) M. A. Tius, Acc.
Chem. Res. 2003, 36, 284–290; e) R. Zimmer, C. U.
Dinesh, E. Nandanan, F. A. Khan, Chem. Rev. 2000,
100, 3067–3126; f) A. Hoffmann-Rçder, N. Krause,
Org. Biomol. Chem. 2005, 3, 387–391.
[4] a) R. Schwesinger, H. Schlemper, Angew. Chem. 1987,
99, 1212–1214; Angew. Chem. Int. Ed. Engl. 1987, 26,
1167–1169; b) T. Pietzonka, D. Seebach, Angew. Chem.
1993, 105, 741–742; Angew. Chem. Int. Ed. Engl. 1993,
32, 716–717; c) R. Schwesinger, et al., Liebigs Ann.
1996, 1055–1081; see also Supporting Information;
d) I. Leito, T. Rodima, I. A. Koppel, R. Schwesinger,
V. M. Vlasov, J. Org. Chem. 1997, 62, 8479–8483;
e) G. A. Kraus, N. Zhang, J. G. Verkade, M. Nagarajan,
P. B. Kisanga, Org. Lett. 2000, 2, 2409–2410; f) C. A.
Sandoval, T. Ohkuma, K. Muniz, R. Noyori, J. Am.
Chem. Soc. 2003, 125, 13490–13503.
[5] a) T. Imahori, Y. Kondo, J. Am. Chem. Soc. 2003, 125,
8082–8083; b) T. Imahori, C. Hori, Y. Kondo, Adv.
Synth. Catal. 2004, 346, 1090–1092; c) M. Ueno,
A. E. H. Wheatley, Y. Kondo, Chem. Commun. 2006,
3549–3550.
[6] a) M. Ueno, C. Hori, K. Suzawa, M. Ebisawa, Y.
Kondo, Eur. J. Org. Chem. 2005, 1965–1968; b) K. Ko-
bayashi, M. Ueno, Y. Kondo, Chem. Commun. 2006,
3128–3130; c) K. Suzawa, M. Ueno, A. E. H. Wheatley,
Y. Kondo, Chem. Commun. 2006, 4850–4852; d) M.
Ueno, M. Yonemoto, M. Hashimoto, A. E. H. Wheat-
ley, H. Naka, Y. Kondo, Chem. Commun. 2007, 2264–
2266; e) M. Ebisawa, M. Ueno, Y. Oshima, Y. Kondo,
Tetrahedron Lett. 2007, 48, 8918–8921.
of
C28H20NCl, M=405.93, triclinic, space group P-1 (No.2), a=
9.8755(4) Š, b=10.2622(4) Š, c=11.4287(6) Š, a=
83.9049(18)8, b=86.0386(16)8, g=67.04551(12)8, V=
1060.01(8) Š3, T=173.3 K, Z=2, (MoKa)=1.945 cmꢀ1,
5-(4-chlorophenyl)-1,2,3-triphenyl-1-H-pyrrole
3ba:
m
ACHTREUNG
10457 reflections measured, 4798 unique (Rint =0.027). The
final R1 and wR2 were 0.0410 [I>2s (I)] and 0.1113 (for all
data), respectively. {R1=SjjFo jꢀjFcjj/SjFo j, wR2=[S(w
A
G
Supporting Information
Full experimental details and characterization data for all
compounds are given in the electronic Supporting Informa-
tion.
Acknowledgements
This research was partly supported by Grants-in-Aid for Sci-
entific Research on Priority Areas “Advanced Molecular
Transformation of Carbon Resources”, “Synergistic Effects
for Creation of Functional Molecules” (to Y. K.), Grants-in-
Aid for Young Scientists (B) (to H. N.), and IREMC
(Tohoku Univ. Global COE, to H. N.).
[7] Use of various other organic (t-Bu-P2 base, DBU,
DABCO) or organometallic (n-BuLi, t-BuOK,
KHMDS) bases was ineffective under the same condi-
tions.
References
[1] a) R. Zimmer, H.-U. Reissig, Donor-Substituted Al-
lenes, in Modern Allene Chemistry, Vol. 1, (Eds.: N.
Krause, A. S. K. Hashmi), Wiley-VCH, Weinheim,
2004, pp 425–492; b) C. Najera, M. Yus, in: The
Chemistry of Organolithium Compounds, Vol. 2, (Eds.:
Z. Rappoport, I. Marek), Wiley, Chichester, 2006,
pp 258–268; c) L. Brandsma, J. W. Zwikker, in: Science
of Synthesis, Vol. 8a, (Eds.: M. Majewski, V. Snieckus),
Thieme, Stuttgart, 2006, pp 271–283.
[2] Selected references: a) D. Hoppe, C. Riemenschneider,
Angew. Chem. 1983, 95, 64–65; Angew. Chem. Int. Ed.
Engl. 1983, 22, 54; b) D. Hoppe, C. Gonschorrek, D.
Schmidt, E. Egert, Tetrahedron 1987, 43, 2457–2466;
c) A. R. Katritzky, D. Feng, H. Lang, J. Org. Chem.
1997, 62, 715–720; d) C. Schultz-Fademrecht, B. Wibb-
eling, R. Frçhlich, D. Hoppe, Org. Lett. 2001, 3, 1221–
1224; e) C. Schultz-Fademrecht, M. A. Tius, S. Grimme,
B. Wibbeling, D. Hoppe, Angew. Chem. 2002, 114,
[8] a) G. W. Gribble, in: Comprehensive Heterocyclic
Chemistry II, Vol. 2, (Eds.: A. R. Katritzky, C. W. Rees,
E. F. V. Scriven), Elsevier, Oxford, U.K., 1996, pp 207–
257; b) N. T. Patil, Y. Yamamoto, ARKIVOC 2007, 10,
121–141; c) G. Balme, Angew. Chem. 2004, 116, 6396–
6399; Angew. Chem. Int. Ed. 2004, 43, 6238–6241.
[9] Recent examples: a) D. J. St. Cyr, N. Martin, B. A.
Arndtsen, Org. Lett. 2007, 9, 449–452; b) C. V. Galli-
ford, K. A. Scheidt, J. Org. Chem. 2007, 72, 1811–1813;
c) I. Bergner, T. Opatz, J. Org. Chem. 2007, 72, 7083–
7090; d) M. Shindo, Y. Yoshimura, M. Hayashi, H. Soe-
jima, T. Yoshikawa, K. Matsumoto, K. Shishido, Org.
Lett. 2007, 9, 1963–1966.
[10] The molecular structure of 3ba has been unambiguous-
ly determined by single-crystal X-ray structural analy-
sis. CCDC 671214 contains the supplementary crystal-
lographic data for this paper. These data can be ob-
Adv. Synth. Catal. 2008, 350, 1901 – 1906
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
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Hiroshi Naka et al.
FULL PAPERS
tained free of charge from The Cambridge Crystallo-
graphic Data Centre via www.ccdc.cam.ac.uk/data_
request/cif or from the Cambridge Crystallographic
Data Centre, 12 Union Road, Cambridge CB21EZ,
UK [fax: (+44)1223–336–033; or deposit@ccdc.cam.a-
c.uk].
599–602; c) J. P. Sonye, K. Koide, J. Org. Chem. 2006,
71, 6254–6257.
[12] A. E. Mattson, A. R. Bharadwaj, A. M. Zuhl, K. A.
Scheidt. , J. Org. Chem. 2006, 71, 5715–5724.
[13] G. M. Sheldrick, SHELXL-97, Program for the Refine-
ment of Crystal Structures, University of Gçttingen,
Germany, 1997.
[11] a) J. P. Sonye, K. Koide, Org. Lett. 2006, 8, 199–202;
b) J. P. Sonye, K. Koide, Synth. Commun. 2006, 36,
1906
asc.wiley-vch.de
ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2008, 350, 1901 – 1906