Facile and selective synthesis of propargylic amines and 1,6-diynes: One-pot three-component coupling reactions of alkynylsilanes, aldehydes and amines by a cooperative catalytic system comprised of CuCl and Cu(OTF) 2

Article abstract of DOI:10.1055/S-2008-1077790

Described herein is a three-component coupling reaction of alkynylsilanes, aldehydes and amines by a cooperative catalytic system comprised of CuCl and Cu(OTf)₂, leading to the production of a variety of propargyl amine derivatives. This catalytic system was successfully applied to the practical preparation of 1,6-diyne derivatives via twice-performed, domino-type coupling reactions.

Full text of DOI:10.1055/S-2008-1077790

LETTER
1515
Facile and Selective Synthesis of Propargylic Amines and 1,6-Diynes: One-Pot
Three-Component Coupling Reactions of Alkynylsilanes, Aldehydes and
Amines by a Cooperative Catalytic System Comprised of CuCl and Cu(OTf)2
F
acile andSelectiv
o
e
Synthesis
o
f
Propa
i
rgylic
A
o
mines and 1,6-Diy
S
nes akai,* Naoki Uchida, Takeo Konakahara
Department of Pure and Applied Chemistry, Faculty of Science and Technology, Tokyo University of Science (RIKADAI),
Noda, Chiba 278-8510, Japan
E-mail: sakachem@rs.noda.tus.ac.jp
Received 10 March 2008
somi, in which the silyl group of alkynylsilanes was
Abstract: Described herein is a three-component coupling reaction
cleaved by CuCl in a unique polar solvent to generate a
copper acetylide, followed by a coupling reaction of the
acetylide with acyl chlorides, which produced a-
of alkynylsilanes, aldehydes and amines by a cooperative catalytic
system comprised of CuCl and Cu(OTf)2, leading to the production
of a variety of propargyl amine derivatives. This catalytic system
was successfully applied to the practical preparation of 1,6-diyne alkynones.8g Based on this result, we examined a novel
derivatives via twice-performed, domino-type coupling reactions.
three-component coupling reaction of alkynylsilanes, al-
dehydes, and amines utilizing the activation of the C–Si
bond principally using a copper catalyst. In this letter, we
report the preliminary results wherein a cooperative cata-
lytic system consisting of CuCl and Cu(OTf)2 promoted a
three-component coupling reaction of alkynylsilanes, al-
dehydes, and amines, producing polyfunctionalized prop-
argylic amine derivatives. Herein, we also disclose that
the use of formaldehyde as the reaction substrate selec-
tively produced 1,6-diyne derivatives in good yields via
twice-performed, domino-type three-component coupling
reactions.
Keyword: multicomponent coupling reaction, copper catalyst,
alkynylsilane, propargylic amine, 1,6-diyne
The facile and practical preparation of multifunctional-
ized propargyl amines is attractive and important, since a
number of their derivatives constitute basic units in natu-
rally occurring products and related biologically active
substances.1 Until now, the major approach to the prepa-
ration of these compounds has been the nucleophilic addi-
tion of a variety of alkynyl metals to carbon electrophiles,
such as imines,2 enamines,3 nitrones,4 acetals5 and ami-
nals.6 Quite recently, a metal-promoted three-component
coupling reaction of alkynes, aldehydes, and amines, lead-
ing to propargylic amines in an organic–aqueous medium,
has been favored by organic and pharmaceutical chemists,
because of the achievement of a multibond formation in a
single step and its facile operation in the experiment.7 On
the other hand, alkynylsilanes have been widely employed
as a convenient partner in common organic reactions, due
to ready availability and a high tolerance to functional
groups.8 However, reactions using convenient silane com-
pounds as substrates in multicomponent coupling reac-
tions, as described above, have rarely been reported. In
addition, development of a new method for direct activa-
tion of an alkynylsilane without an additive, such as a flu-
oride ion and a base, would enable us to clear a new aspect
of organosilicon chemistry. We therefore planned the de-
velopment of a novel multicomponent coupling reaction
using an alkynylsilane. Taking into account the harmful
influence of a chemical process apparatus and environ-
mental impact, we intended to avoid the use of the cata-
lyst, which produces a fluoride ion, to activate the carbon–
silicon bond in an alkynylsilane. Thus, we focused our at-
tention on the interesting results reported by Ito and Ho-
As a model reaction, we initially examined the three-com-
ponent coupling of 1-phenyl-2-(trimethylsilyl)acetylene
Table 1 Examination of Reaction Conditionsa
MeO
OMe
SiMe3
N
cat.
+
+
N
H
Ph
CHO
3a
1a
Ph
4
2a
Entry Catalyst (mol%)
Solvent
Time (h) Yield (%)b
1
2
3
4
5
6
7
8
9
CuCl (10)
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
1,4-dioxane
24
24
24
24
24
24
6
87
Cu(OTf)2 (10)
AgOTf (10)
AlCl3 (10)
83
78
NDc
NDc
NDc
96
Zn(OTf)2 (10)
Hf(OTf)4 (10)
CuCl (5) + Cu(OTf)2 (5) 1,4-dioxane
CuCl (5) + Cu(OTf)2 (5) MeCN
2
99
SYNLETT 2008, No. 10, pp 1515–1519
Advanced online publication: 16.05.2008
x
x
.x
x
.2
0
0
8
none
meCN
24
48
a Molar ratio: alkyne 1a/aldehyde 2a/amine 3a = 1.2:1:1.2.
b Isolated yield.
c ND: not determined.
DOI: 10.1055/s-2008-1077790; Art ID: U01608ST
© Georg Thieme Verlag Stuttgart · New York

1516
N. Sakai et al.
LETTER
(1a), p-methoxybenzaldehyde (2a), and piperidine (3a) in summarized in Table 2. Based on the results in Table 1,
the presence of CuCl in 1,4-dioxane under reflux condi- for example, when the reaction was run using benzalde-
tions. As a result, the expected reaction proceeded cleanly hydes 2b and 2c having a hydroxyl group and a chloro
to produce the desired propargylic amine 4 in 87% yield substituent, and piperidine (3a), the desired reaction was
(Table 1, entry 1).9 Similarly, when the reaction was run completed in a short time (<3 h) to produce the corre-
with Cu(OTf)2, the same propargylic amine was obtained sponding propargyl amine derivatives 5 and 6 in good to
in 83% yield (entry 2). AgOTf also showed a similar ef- excellent yields (entries 2 and 3). Additionally, this cop-
fect for the reaction (entry 3). However, a typical Lewis per catalytic system accommodated various heterocyclic
acid, such as AlCl3, Zn(OTf)2 and Hf(OTf)4 was ineffec- aldehydes, aliphatic aldehydes and paraformaldehyde
tive in the coupling reaction and resulted in the recovery (entries 4–8). Alternatively, use of 2-formylpyridine (2f)
of the starting materials (entries 4–6). It is noteworthy that led to a coupling reaction to produce the corresponding
when the reaction was performed using a catalytic system propargylic amine 9 in only 13% yield, but the indolizine
comprised of both Cu(OTf)2 and CuCl, the reaction time derivative 9¢, which was formed through intramolecular
was shortened to within six hours, and the yield was en- cycloisomerization of the amine 9, was isolated as the ma-
hanced to a nearly quantitative yield (entry 7). Moreover, jor product (56%; entry 6). The detailed results will be
it was found that the use of MeCN instead of 1,4-dioxane discussed below. When the reaction was run using other
further reduced the reaction time. These reaction condi- cyclic amines and aliphatic amines, such as morpholine,
tions were the best for the coupling reaction (entry 8).10
N-methylpiperazine, diethylamine or diallylamine, the
corresponding products were also obtained in good to ex-
cellent yields (entries 9–12). On the other hand, when a
primary amine, such as butylamine or benzylamine was
To generalize the reaction, the coupling reaction of alky-
nylsilane 1a with various aldehydes and amines, was car-
ried out under optimal conditions. The results are
Table 2 Synthesis of a Variety of Propargylic Aminesa
R1
NR2(NHR)
SiMe3
R1CHO
5 mol% CuCl
2
5 mol% Cu(OTf)2
+
MeCN, reflux
Amine
Ph
Ph
4–18
3
1a
Entry
Aldehyde R1
Amine
Time (h)
Yield (%)b
99 (4)
1
2
3
4
5
6
7
8
9
p-MeOC6H4
o-HOC6H4
p-ClC6H4
2-furyl
2a
2b
2c
2d
2e
2f
piperidine
piperidine
piperidine
piperidine
piperidine
piperidine
piperidine
piperidine
morpholine
3a
3a
3a
3a
3a
3a
3a
3a
3b
2
3
75 (5)
2
99 (6)
6
45 (7)
2-thienyl
2-pyridyl
n-Pr
6
57 (8)
2
13 (9)c
75 (10)
72 (11)
98 (12)
2g
2h
2a
12
12
2
Hd
p-MeOC6H4
10
p-MeOC6H4
2a
3c
2
92 (13)
MeN
NH
11
12
13
14
15
p-MeOC6H4
p-MeOC6H4
p-MeOC6H4
p-MeOC6H4
p-MeOC6H4
2a
2a
2a
2a
2a
Et2NH
3d
3e
3f
4
6
95 (14)
80 (15)
30 (16)
16 (17)
21 (18)
(allyl)2NH
n-BuNH2
t-BuNH2
BnNH2
24
24
24
3g
3h
a Molar ratio: alkyne 1/aldehyde 2/amine 3 = 1.5:1:1.2.
b Isolated yield.
c Indolizine 9¢ was formed in 56% yield.
d Paraformaldehyde was used.
Synlett 2008, No. 10, 1515–1519 © Thieme Stuttgart · New York

LETTER
Facile and Selective Synthesis of Propargylic Amines and 1,6-Diynes
1517
used, the reaction required a longer reaction time, and the Table 3 Synthesis of Symmetrical 1,6-Diynesa
yield was drastically reduced to less than 30% (entries 13–
15).
R3
N
R2
R2
SiMe3
5 mol% CuCl
5 mol% Cu(OTf)2
R3NH2
The reaction of several alkynylsilanes 1 with p-methoxy-
benzaldehyde (2a) and piperidine (3a) was then conduct-
ed under optimal conditions (Scheme 1). For example,
when the reactions were run with the alkyne involving an
aliphatic group, such as a hexyl and a methyl group, the
reactions proceeded cleanly producing the corresponding
propargylic amines 19 and 20 in good to excellent yields.
Interestingly, the use of an internal alkyne having both a
TBS (t-butyldimethylsilyl) group and a TMS group pro-
duced the propargylic amine 21 quantitatively, in which
the more bulky TBS group remained on the terminal car-
bon. This result indicates that the copper catalytic system,
due to the steric effect for substituents on the silicon atom,
selectively cleaved the smaller substituent, the TMS
group. Similarly, when the reaction was conducted with
trimethylsilylacetylene, the desired propargylic amine 22
with no substituent group on the carbon–carbon triple
bond was obtained in good yield.
+
R2CHO
+
MeCN, reflux, 24 h
2
3
R1
R1
R1
1
Entry R1
R2
R3
Yield (%)b Diyne
1
2
3
4
5
6
7
8
Ph
Hc
Hc
Hc
Hc
Hc
Bn
80
23
24
25
26
27
18
28
29
Ph
n-Bu
Bn
60
C6H13
Me
TBS
Ph
71
Bn
70
Bn
67
p-MeOC6H4
n-Pr
Bn
Bn
Bn
16
Ph
ND
ND
Ph
CF3
a Molar ratio: alkyne 1/aldehyde 2/amine 3 = 3:3:1.
b Isolated yield.
c Paraformaldehyde was used.
MeO
OMe
5 mol% CuCl
5 mol% Cu(OTf)2
SiMe3
N
+
+
5 mol% CuCl
5 mol% Cu(OTf)2
MeCN
reflux, 2 h
CN
CN
N
H
+
+
BnNH2
R1
Me3SiCN
Bn
N
(HCHO)n
R1
MeCN
reflux, 20 h
CHO
2a
3a
30
2h
3h
1
31: 97%
21: 99% (R1 = t-BuMe2Si)
22: 72% (R1 = H)
19: 99% (R1 = C6H13
20: 77% (R1 = Me)
)
Scheme 2
Scheme 1
Recently, several groups have reported the metal-cata-
lyzed cycloisomerization of propargylic pyridine and its
derivatives leading to the preparation of indolizine deriv-
atives.13 These reports strongly motivated us to develop a
more general method for the synthesis of a nitrogen-con-
taining heterocycle from an alkynylsilane, an aldehyde
and an amine in the presence of these copper catalysts.
Thus, when the similar reaction with alkynylsilane 1a, 2-
formylpyridine (2a) and piperidine (3a) was conducted
under conditions shown in Scheme 3, the desired cycloi-
somerization proceeded quantitatively to produce the cor-
responding indolizine 9¢ (vide entry 6 in Table 2).14 It was
found that our copper catalytic system could be success-
fully applied to the synthesis of nitrogen-containing het-
erocycles via intramolecular cycloisomerization.
Then, we anticipated that a reaction using a primary amine
and an excess amount of alkynylsilane and paraformalde-
hyde, would form a symmetrical 1,6-diyne derivative
through consecutive three-component coupling reac-
tions.11 After many examinations it was found that, unlike
the result shown in Table 2, when the coupling reaction of
alkynylsilane 1a (3 equiv) and formaldehyde (2h; 3 equiv)
with benzylamine (3h) was conducted with our copper
catalytic system, the reaction completed cleanly within 24
hours to produce the expected 1,6-diyne 23 in 80% yield
(Table 3, entry 1).12 In addition, this catalytic system ac-
commodated the coupling reaction using n-butylamine
and other types of alkynylsilanes having an aliphatic
group and a TBS group in good yields (entries 2–5). When
the reaction with an aromatic aldehyde, such as p-meth-
oxybenzaldehyde, was carried out, the corresponding pro-
pargylic amine 18 was obtained in a low yield (entry 6).
Unfortunately, an aliphatic aldehyde led to the production
of a complex mixture (entries 7 and 8).
SiMe3
N
[Cu] cat.
+
+
MeCN
reflux, 1 h
N
CHO
N
H
N
Ph
2g (1.5 equiv)
On the other hand, when the reaction was run using tri-
methylsilyl cyanide (30) instead of a silylacetylene, the
expected double Strecker-type reactions cleanly proceed-
ed to produce the corresponding tertiary amine 31 in a
nearly quantitative yield (Scheme 2).
3a
Ph
1a (1.5 equiv)
9': 97%
[Cu] cat.: 5 mol% CuCl + 5 mol% Cu(OTf)2
Scheme 3
Synlett 2008, No. 10, 1515–1519 © Thieme Stuttgart · New York

1518
N. Sakai et al.
LETTER
R. B.; Scheidt, K. A. Org. Lett. 2005, 7, 3227.
There is no clear explanation for the role of each of these
copper catalysts. We assumed that CuCl activates the C–
Si bond of an alkynylsilane to generate a copper acetyl-
ide,8g,i,15 and that Cu(OTf)2 has a role, in which it behaves
as a Lewis acid for in situ generation of the iminium inter-
mediate, which forms from the starting materials, an alde-
hyde and an amine.
(e) Nishihara, Y.; Ikegashira, K.; Hirabayashi, K.; Ando, J.-
I.; Mori, A.; Hiyama, T. J. Org. Chem. 2000, 65, 1780.
(f) Abele, E.; Rubina, K.; Abele, R.; Popelis, J.; Mazeika, I.;
Lukevics, E. J. Organomet. Chem. 1999, 586, 184. (g) lto,
H.; Arimoto, K.; Sensui, H.; Hosomi, A. Tetrahedron Lett.
1997, 38, 3977. (h) Hayashi, M.; Inubushi, A.; Mukaiyama,
T. Chem. Lett. 1987, 16, 1975. (i) Ikegashira, K.; Nishihara,
Y.; Hirabayashi, K.; Mori, A.; Hiyama, T. Chem. Commun.
1997, 1039.
Thus far, we have demonstrated that a cooperative catalyt-
ic system comprised of CuCl and Cu(OTf)2 effectively
catalyzes a three-component coupling reaction of alkynyl-
silanes, aldehydes, and primary/secondary amines to pro-
duce a variety of propargylic amine derivatives in
moderate to excellent yields. We have also found that use
of an excess amount of paraformaldehyde and alkynylsi-
lanes selectively produced 1,6-diyne derivatives in good
yields through twice-performed, domino-type three-com-
ponent coupling reactions.
(9) General Procedure for the Synthesis of a Propargyl
Amine: To a MeCN solution (300 mL) in a screw-capped
vial under an N2 atmosphere, alkynylsilane 1 (0.45 mmol),
aldehyde 2 (0.30 mmol), amine 3 (0.36 mmol), Cu(OTf)2
(5.4 mg, 0.015 mmol) and CuCl (1.5 mg, 0.015 mmol) were
successively added, and the vial was sealed with a cap
containing a PTFE septum. The reaction mixture was heated
at 100 °C until the reaction was completed as monitored by
TLC. After the reaction, the mixture was directly subjected
to SiO2 gel without the usual extraction, and was purified by
flash column chromatography (hexane–EtOAc) to give the
corresponding propargyl amines in the yields shown in
Table 2.
Acknowledgment
1-[1-(4-Methoxyphenyl)-3-phenylpropyn-2-yl]-4-methyl-
piperazine (13): pale yellow oil. 1H NMR (500 MHz,
CDCl3): d = 2.21 (s, 3 H), 2.40 (m, 4 H), 2.59 (m, 4 H), 3.74
(s, 3 H), 4.69 (s, 1 H), 6.82 (d, J = 7.5 Hz, 2 H), 7.23 (m, 3
H), 7.42 (m, 2 H), 7.46 (d, J = 7.5 Hz, 2 H). 13C NMR (125
MHz, CDCl3): d = 46.0, 48.8, 55.3, 55.3, 61.0, 85.7, 88.1,
113.4, 113.5, 123.2, 128.0, 128.2, 129.6, 130.4, 131.8,
159.1. MS (EI): m/z = 320. HRMS (FAB): m/z calcd for
C21H24N2O: 320.1889; found: 320.1876.
N-(tert-Butyl)-1-(4-methoxyphenyl)-3-phenylprop-2-yn-1-
amine (17): colorless oil. 1H NMR (500 MHz, CDCl3): d =
1.26 (s, 9 H), 3.80 (s, 3 H), 4.80 (s, 1 H), 6.89 (d, J = 7.5 Hz,
2 H), 7.29 (m, 3 H), 7.42 (m, 2 H), 7.51 (d, J = 7.5 Hz, 2 H).
13C NMR (125 MHz, CDCl3): d = 29.9, 48.2, 51.2, 55.3,
84.1, 92.8, 113.9, 123.6, 127.9, 128.2, 128.5, 131.4, 135.0,
158.9. MS (EI): m/z = 293. HRMS (FAB): m/z calcd for
C20H23NO: 293.1780; found: 293.1785.
This work was partially supported by a grant for a ‘High-Tech Re-
search Center’ project awarded to private universities and a
matching fund subsidy from MEXT, 2000-2004, and 2005-2007.
References and Notes
(1) In Encyclopedia of the Alkaloids; Glasby, J. S., Ed.; Plenum
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(2) (a) Jiang, B.; Si, Y.-G. Tetrahedron Lett. 2003, 44, 6767.
(b) Wei, C.; Li, C. J. J. Am. Chem. Soc. 2002, 124, 5638.
(c) Fischer, C.; Carreira, E. M. Org. Lett. 2001, 3, 4319.
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(5) (a) Sakai, N.; Kanada, R.; Hirasawa, M.; Konakahara, T.
Tetrahedron 2005, 61, 9298. (b) Sakai, N.; Hirasawa, M.;
Konakahara, T. Tetrahedron Lett. 2003, 44, 4171.
(c) Fleming, J. J.; Fiori, K. W.; Du Bois, J. J. Am. Chem. Soc.
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(6) (a) Gommermann, N.; Koradin, C.; Knochel, P. Synthesis
2002, 2143. (b) Ahn, J. H.; Joung, M. J.; Yoon, N. M.;
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(10) When a similar coupling reaction was carried out with
phenylacetylene, propargylic amine 4 was obtained in a 61%
yield (7 h).
(11) (a) Bonfield, E. R.; Li, C.-J. Org. Biomol. Chem. 2007, 5,
435. (b) Sakaguchi, S.; Mizuta, T.; Furuwan, M.; Kubo, T.;
Ishii, Y. Chem. Commun. 2004, 1638.
(12) General Procedure for the Synthesis of a Symmetrical
1,6-Diyne: To a MeCN solution (300 mL) in a screw-capped
vial under a N2 atmosphere, alkynylsilane 1 (0.90 mmol),
paraformaldehyde 2h (0.90 mmol), primary amine 3 (0.30
mmol), Cu(OTf)2 (5.4 mg, 0.015 mmol) and CuCl (1.5 mg,
0.015 mmol) were successively added, and the vial was
sealed with a cap containing a PTFE septum. The reaction
mixture was heated at 100 °C for 24 h. After the reaction, the
mixture was directly subjected to SiO2 gel without the usual
extraction, and was purified by flash column
chromatography (hexane–EtOAc) to give the corresponding
1,6-diynes in the yields shown in Table 3.
N-Benzyl-N,N-bis[3-(tert-butyldimethylsilyl)propyn-2-
yl]amine (27): colorless oil. 1H NMR (500 MHz, CDCl3):
d = 0.12 (s, 12 H), 0.96 (s, 18 H), 3.40 (s, 4 H), 3.69 (s, 2 H),
7.32 (m, 5 H). 13C NMR (125 MHz, CDCl3): d = –4.5, 16.5,
26.1, 43.1, 56.9, 88.2, 101.7, 127.3, 128.3, 129.4, 138.0. MS
(EI): m/z = 411. HRMS (FAB): m/z calcd for C25H42NSi2:
412.2856; found: 412.2866.
(8) For selected papers for the reactions using an alkynylsilane,
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Lett. 2006, 47, 5269. (b) Montel, F.; Beaudegnies, R.;
Kessabi, J.; Martin, B.; Muller, E.; Wendeborn, S.; Jung, P.
M. J. Org. Lett. 2006, 8, 1905. (c) Kitazawa, T.; Minowa,
T.; Mukaiyama, T. Chem. Lett. 2006, 35, 1002. (d) Lettan,
Synlett 2008, No. 10, 1515–1519 © Thieme Stuttgart · New York

LETTER
Facile and Selective Synthesis of Propargylic Amines and 1,6-Diynes
1519
(13) (a) Kim, I.; Choi, J.; Won, H. K.; Lee, G. H. Tetrahedron
Lett. 2007, 48, 6863. (b) Yan, B.; Zhou, Y.; Zhang, H.;
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Liu, Y. Org. Lett. 2007, 9, 4323. (d) Seregin, I. V.;
Schammel, A. W.; Gevorgyan, V. Org. Lett. 2007, 9, 3433.
(e) Schwier, T.; Sromek, A. W.; Yap, D. M. L.; Chernyak,
D.; Gevorgyan, V. J. Am. Chem. Soc. 2007, 129, 9868.
(f) Seregin, I. V.; Gevorgyan, V. J. Am. Chem. Soc. 2006,
128, 12050.
(14) Procedure for the Synthesis of 1-Aminoindolizine 9¢: To
a MeCN solution (300 mL) in a screw-capped vial under a N2
atmosphere, alkynylsilane 1a (78 mg, 0.45 mmol), aldehyde
2g (48 mg, 0.45 mmol), amine 3a (26 mg, 0.30 mmol) and
Cu(OTf)2 (5.4 mg, 0.015 mmol) were successively added,
and the vial was sealed with a cap containing a PTFE
septum. The reaction mixture was heated at 100 °C for 1 h.
After the reaction, the mixture was directly subjected to
Al2O3 gel without the usual extraction, and was purified by
flash column chromatography (hexane–EtOAc) to give 1-
aminoindolizine 9¢ in 97% yield (80 mg).
3-Phenyl-1-piperidin-1-ylindolizine (9¢): yellow oil. 1H
NMR (500 MHz, CDCl3): d = 1.50 (quint, J = 6.0 Hz, 2 H),
1.71 (quint, J = 6.0 Hz, 4 H), 2.94 (t, J = 6.0 Hz, 4 H), 6.30
(t, J = 7.5 Hz, 1 H), 6.44 (t, J = 7.5 Hz, 1 H), 6.60 (s, 1 H),
7.22 (t, J = 7.5 Hz, 1 H), 7.36 (m, 3 H), 7.47 (d, J = 7.0 Hz,
2 H), 8.11 (d, J = 7.5 Hz, 1 H). 13C NMR (125 MHz, CDCl3):
d = 24.4, 26.5, 55.2, 105.7, 110.7, 114.3, 118.1, 121.6, 126.7,
127.5, 127.7, 128.6, 128.9, 131.1, 132.6. MS (EI): m/z = 276.
(15) Nishihara, Y.; Takemura, M.; Mori, A.; Osakada, K.
J. Organomet. Chem. 2001, 620, 282.
Synlett 2008, No. 10, 1515–1519 © Thieme Stuttgart · New York

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