Rare-earth silylamide-catalyzed selective dimerization of terminal alkynes and subsequent hydrophosphination in one pot

Article abstract of DOI:10.1021/jo0509206

Rare-earth silylamides, Ln[N(SiMe₃)₂]₃ (Ln = Y, La, Sm), catalyzed regio- and stereoselective dimerization of terminal alkynes in the presence of amine additives to give conjugated enynes in high yields. The additives play

Full text of DOI:10.1021/jo0509206

Rare-Earth Silylamide-Catalyzed Selective Dimerization of
Terminal Alkynes and Subsequent Hydrophosphination
in One Pot
Kimihiro Komeyama,* Tomonori Kawabata, Katsuomi Takehira, and Ken Takaki*
Department of Chemistry and Chemical Engineering, Graduate School of Engineering,
Hiroshima University, Kagamiyama, Higashi-Hiroshima 739-8527, Japan
kkome@hiroshima-u.ac.jp
Received May 9, 2005
Rare-earth silylamides, Ln[N(SiMe3)2]3 (Ln ) Y, La, Sm), catalyzed regio- and stereoselective
dimerization of terminal alkynes in the presence of amine additives to give conjugated enynes in
high yields. The additives played a crucial role to depress the oligomerization and to control the
regio- and stereochemistry of the dimerization. Thus, the selectivity for (Z)-head-to-head enynes
was increased in the order of tertiary < secondary < primary amine additives. On the other hand,
the reversed order was observed for the formation of head-to-tail dimers. When R,ω-diynes were
subjected to the dimerization, very novel cyclic bisenyne compounds were given through double-
dimerization in satisfactory yields. In addition, an application of the system allowed subsequent
hydrophosphination of the enynes generated in situ with diphenylphosphine, giving rise to
1-phosphinyl-1,3-dienes as the sole products in excellent yields after oxidative workup.
Introduction
for the alkyne dimerization.4 Preparation of these com-
plexes needs multisteps despite their good catalyst activi-
ties.7 In contrast, readily available rare-earth silylamides,
Ln[N(SiMe3)2]3, would be potentially attractive catalysts,
Enyne compounds have been known as important
building blocks in organic synthesis1 and as key units
found in a variety of biologically active compounds.2 Of
their synthetic methods, the dimerization of terminal
alkynes could be a very practical and straightforward
approach in an atom-economical manner. For this reason,
the reaction has been frequently investigated with use
of many metal catalysts, which include group 4 and 8-10
metals,3 lanthanides,4 actinides,5 and others.6 However,
exclusive formation of one enyne out of three possible
isomers: (Z), (E)-head-to-head and head-to-tail dimers,
could be achieved with only a few catalysts.3c,f,h,4b More-
over, effective catalysts for the dimerization of both
aromatic and aliphatic alkynes have been rarely re-
ported.6 With respect to lanthanide catalysts, only met-
allocene and half-metallocene complexes have been used
(3) Zr: (a) Horton, A. D. J. Chem. Soc., Chem. Commun. 1992, 185-
187. Ru: (b) Yi, C. S.; Liu, N. Orgaometallics 1996, 15, 3968-3971.
(c) Qu, J. P.; Masui, D.; Ishii, Y.; Hidai, M. Chem. Lett. 1998, 1003-
1004. (d) Bassetti, M.; Marini, S.; Tortorella, F.; Cadierno, V.; Diez,
J.; Gamasa, M. P.; Gimeno, J. J. Organomet. Chem. 2000, 593-594,
292-298. Ir: (e) Ohmura, T.; Yorozuya, S.; Yamamoto, Y.; Miyaura,
N. Organometallics 2000, 19, 365-367. Pd: (f) Trost, B. M.; Sorum,
M. T.; Chan, C.; Harms, A. E.; Ruhter, G. J. Am. Chem. Soc. 1997,
119, 698-708. (g) Lucking, U.; Pfaltz, A. Synlett 2000, 1261-1264.
(h) Rubina, M.; Gevorgyan. V. J. Am. Chem. Soc. 2001, 123, 11107-
11108.
(4) (a) Heeres, H. J.; Teuben, J. H. Organometallics 1991, 10, 1980-
1986. (b) Nishiura, M.; Hou, Z.; Wakatsuki, Y.; Yamaki, T.; Miyamoto,
T. J. Am. Chem. Soc. 2003, 125, 1184-1185. (c) Tazelaar, C. G. J.;
Bambirra, S.; Leusen, D.; Meetsma, A.; Hessen, B.; Teuben, J. H.;
Organometallics 2004, 23, 936-939.
(5) (a) Haskel, A.; Straub, T.; Dash, A. K.; Eisen, M. S. J. Am. Chem.
Soc. 1999, 121, 3014-3024. (b) Wang, J.; Kapon, M.; Berthet, J. C.;
Ephritikhine, M.; Eisen, M. S. Inorg. Chim. Acta 2002, 334, 183-192.
(6) Dash, A. K.; Eisen, M. S. Org. Lett. 2000, 2, 737-740.
(7) Jesk, G.; Lauke, H.; Mauermann, H.; Swepston, P. N.; Schu-
mann, H.; Marks, T. J. J. Am. Chem. Soc. 1985, 107, 8091-8103.
(1) (a) Trost, B. M. Science 1991, 254, 1471-1477. (b) Trost, B. M.
Angew. Chem., Int. Ed. Engl. 1995, 34, 259-281.
(2) Nicolaou, K. C.; Dai, M. W.; Tsay, S. C.; Estevez, V. A.; Wrasidlo,
W. Science 1992, 256, 1172-1178.
10.1021/jo0509206 CCC: $30.25 © 2005 American Chemical Society
Published on Web 07/28/2005
7260
J. Org. Chem. 2005, 70, 7260-7266

Silylamide-Catalyzed Selective Dimerization of Terminal Alkynes
TABLE 1. Effect of Amine Additives for Dimerization of
Terminal Alkynes 1 Catalyzed by the Rare-Earth
Silylamide
because they are found to be effective for hydroamina-
tion,8 hydrosilylation,9 and hydrophosphination10 of un-
saturated bonds as well as the lanthanocenes. In fact,
we recently reported that regio- and stereoselective
dimerization of various functional terminal alkynes was
induced by the amide complexes.11 In this paper, we
describe more detailed features of the reaction, particu-
larly, the scope and limitation, and double-dimerization
of R,ω-diynes leading to cyclic bisenynes. As an applica-
tion of the present method, one-pot synthesis of 1-phos-
product and
yieldb (%)
convb
(%)
phinyl-1,3-butadiene derivatives through the dimeriza-
tion and subsequent hydrophosphination using the single
catalyst is also documented herein.
entry
R
Ln
Y
additivea
2
3
4
1
2
Ph (1a)
none
97
95
94
5
2
1
11
7
2
3
0
2
0
0
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
Et3N
3
Ph3N
37
4
Ph2NH
C5H11NH2
PhNH2
88 22 35
Results and Discussion
5
99
90
0
0
0
0
0
0
0
0
0
70
87
9
6
When phenylacetylene (1a) was treated with
Y[N(SiMe3)2]3 (5 mol %) in toluene at 100 °C for 17 h,
97% of 1a was consumed, but head-to-tail dimer, 2,4-
diphenylbut-1-en-3-yne (2a), and head-to-head dimer, (Z)-
and (E)-1,4-diphenylbut-1-en-3-yne (3a) and (4a) were
obtained only in 5%, 11%, and 2% yields, respectively.
The low mass balance was attributed to the formation of
oligomers, which were not fully characterized. The se-
lectivities of 2a-4a hardly changed even by decrease of
the conversion 1a at lower temperature (60 °C). The
reaction became sluggish in THF, wherein 2a was given
in 17% yield as a single product with 50% conversion
after 46 h at refluxing temperature. Then, we investi-
gated the effect of various additives in order to improve
the product yield and selectivity. An addition of Ph3P,
Ph2PH, and Ph2O showed no significant effect and PhOH
ceased the reaction. Fortunately, amine additives exhib-
ited a different effect to produce the dimer 3a with much
improved selectivity. These results are summarized in
Table 1. Tertiary aliphatic amines such as Et3N showed
no effect for inhibition of the oligomerization (entry 2),
but Ph3N slightly increased the yield of 3a to 37% (entry
3). With secondary amine, Ph2NH, the enyne 3a was
obtained in similar yield, but head-to-tail enyne 2a was
also provided in 22% yield (entry 4). Surprisingly, good
regio- and stereospecific dimerization was caused by
C5H11NH2 in high yield (entry 5). Moreover, better yield
was attained by the addition of PhNH2 (entry 6). These
results indicate that the selectivity of 3a is increased in
the order of tertiary < secondary < primary-amine, and
higher reactivity is observed by aromatic amines rather
than aliphatic ones. We next tested the effect of substi-
tuted aromatic primary amines. Bulky amines such as
2,6-iPr2C6H3NH2 predominantly caused the alkyne to
oligomerize (entry 7), whereas both electron-donating and
-withdrawing groups substituted at the para position
7
2,6-iPr2C6H3NH2 >99
8
4-MeOC6H4NH2
4-MeC6H4NH2
4-FC6H4NH2
97
98
96
92
94
95
95
76
94
91
48
58
5
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
4-ClC6H4NH2
Sm
La
Y
hexyl (1h)
none
98 62
Et3N
>99 73
7
Ph3N
92 69 20
Et2NH
Ph2NH
C5H11NH2
PhNH2
DBU
90 48
8
93 60 45
94
30
>99
0
0
9
13
17
8
quinuclidine
N(SiMe3)3
>99 58
>99 92
>99 29
9
5
Sm
La
7
>99 35 13
a The additive was pretreated with the catalyst for 1 h at room
temperature. b Determined by GC.
gave exclusively the enyne 3a in more than 90% yield,
except for 4-MeC6H4NH2 (entries 8-11). Comparing the
metal size of the lanthanide catalysts, smaller Y is
superior to larger Sm and La (entries 11-13).
In the reaction of oct-1-yne (1h) without an additive,
the dimerization proceeded mainly to afford the 2-hexyl-
dec-1-en-3-yne (2h) and (Z)-hexadec-7-en-9-yne (3h) in
62% and 5% yield, respectively. When the screening of
various amine additives was performed in a similar
manner, their effect was found to be very different from
that observed in the dimerization of the aromatic alkyne
1a (Table 1, entries 14-23). Addition of Et3N gave a
better yield of 2h (73%) than Ph3N (entries 15 and 16).
The yield and selectivity decreased with the secondary
amines, wherein Et2NH gave the lowest product selectiv-
ity in the screening (entries 17 and 18). Although the
addition of C5H11NH2 and PhNH2 resulted in the exclu-
sive formation of 3h (entries 19 and 20), they seemed to
depress the catalyst activity. Thus, it can be concluded
that selectivity for the synthesis of the head-to-tail dimer
from the aliphatic alkyne 1h increased in the order of
primary < secondary < tertiary-amine additive, and that
aliphatic amines were superior to aromatic additives, in
sharp contrast to the results in the dimerization of 1a.
Other strong organic bases such as DBU (1,8-diazabicyclo-
[5.4.0]undec-7-ene) and quinuclidine (1-azabicyclo[2.2.2]-
octane) exhibited an undesirable effect, resulting in the
predominant oligomerization with the former base and
(8) (a) Kim, Y. K.; LivingHouse, T.; Bercaw, J. E. Tetrahedron Lett.
2001, 42, 2933-2935. (b) Kim, Y. K.; LivingHouse, T. Angew. Chem.,
Int. Ed. 2002, 41, 3645-3647. (c) Kim, Y, K.; LivingHouse, T.; Horino,
Y. J. Am. Chem. Soc. 2003, 125, 9560-9561. (d) Hong, S. W.; Tian, S.;
Metz, M. V.; Marks, T. J. J. Am. Chem. Soc. 2003, 125, 14768-14783.
(9) (a) Horino, Y.; LivingHouse, T. Organometallics 2004, 23, 12-
14.
(10) (a) Takaki, K.; Takeda, M.; Koshoji, G.; Shishido, T.; Takehira,
K, Tetrahedron Lett. 2001, 42, 6357-6360. (b)Takaki, K.; Koshoji, G.;
Komeyama, K.; Takeda, M.; Shishido, T.; Kitani, A.; Takehira, K. J.
Org. Chem. 2003, 68, 6554-6565. (c) Kawaoka, A. M.; Douglass, M.
R.; Marks, T. J. Organometallics 2003, 22, 4630-4632.
(11) Komeyama, K.; Takehira, K.; Takaki, K. Synthesis 2004, 1062-
1066.
J. Org. Chem, Vol. 70, No. 18, 2005 7261

Komeyama et al.
TABLE 2. Examples of Dimerization of Terminal
Alkynes 1
SCHEME 1
SCHEME 2
product and yielda (%)
entry
R
additive
2
3
1
2
Ph (1a)
4-ClC6H4NH2
0
0
0
0
0
0
0
90 (91)
93 (95)
90 (97)
89 (90)
80 (95)
(27)
75 (77)
tr
(5)
43 (45)
4-MeOC6H4 (1b)
4-MeC6H4 (1c)
4-BrC6H4 (1d)
4-FC6H4 (1e)
3
4
5
6
2-MeC6H4 (1f)
7b
8
butyl (1g)
hexyl (1h)
N(SiMe3)2
C5H11NH2
85 (99)
89 (92)
0
9
10
a Isolated yield. The value in parentheses indicates GC yield.
b 10 mol % of the catalyst and additive were used.
monomer and dimer could be generated in situ through
coordination or ligand exchange with the silylamide.13 Of
course, no reaction took place with these additives alone
and their excess loading lowered the catalyst activity.14
As regards the regioselectivity of the reaction, the alkyne
would insert preferentially to the alkynide coordinated
by bulky amine through the transition state A as depicted
in Scheme 1. On the other hand, the dimerization with
primary amine would proceed via B to avoid the steric
hindrance between substituents of the alkynes. The
formation of the (Z)-isomer of the two head-to-head
dimers may be accounted for by the participation of
dimeric alkynide species.4b
Performing the head-to-tail dimerization of R,ω-diynes
potentially enables two distinctive processes, i.e., mono-
and double-dimerization to afford (n + 3) and (2n + 6)-
membered rings, respectively, as shown in Scheme 2.
With respect to the former reaction, Trost has employed
the palladium-catalyzed reaction to obtain mono cyclic
head-to-tail enynes.15 In addition, Hidai has reported the
synthesis of cyclic (Z)-head-to-head enynes from R,ω-
diynes catalyzed by ruthenium complexes.16 To the best
of our knowledge, there is no precedent of a direct
synthesis of cyclic bisenynes from R,ω-diynes by the
double-dimerization. However, we expected that R,ω-
diynes containing a short carbon chain would dimerize
intermolecularly at first due to the steric reason, which
would be followed by intramolecular dimerization instead
of oligomerization, because the resulting two terminal
alkyne units would come close together by coordination
to the electron-deficient rare-earth metal center.
lower yields with the latter (entries 21 and 22). Finally,
a bulky tris(trimethylsily)amine, N(SiMe3)3, gave 2h and
3h in 92% and 5% yields, respectively (entry 23). The
smaller metal, i.e., Y, gave better results as in the case
of 1a (entries 23-25).
We next investigated the scope of terminal alkynes
under the optimized conditions (Table 2). The reaction
of aromatic alkynes 1b-e with electron-donating and
-withdrawing groups at the para position of the aromatic
ring gave the corresponding enynes 3b-e in high yields
(entries 2-5). However, the presence of an ortho sub-
stituent such as 1-ethynyl-2-methylbezene (1f) resulted
in lower yield of the product 3f (27%) with retention of
the substrate (entry 6). The problem could be overcome
by increasing the catalyst loading to give 3f in 77% yield
(entry 7). The dimerization could not be applied to
aromatic alkynes containing acetyl, ester, and dioxolanyl
groups at the para position.12 In the reaction of aliphatic
alkynes using N(SiMe3)3, 2g and 2h were provided in 92%
and 99% yield, respectively (entries 8 and 9). Substitution
of the tertiary amine by a primary amine like amylamine
enabled exclusive formation of (Z)-head-to-head dimer 3g,
though in low yield (entry 10).
When the silylamide complex was substituted by
lithium hexamethyldisilazane, LiN(SiMe3)2, no reactions
of the terminal alkynes took place under the identical
conditions. The result indicated that the present dimer-
ization is owing to the useful characteristics of the rare-
earth silylamide. By referring to the work of Teuben4a
and Hou,4b it is almost certain that the dimerization
proceeded through alkyne insertion to the rare-earth
alkynide, followed by protonation with another molecule
of the alkyne to give the enyne and the alkynide. The
present reaction sharply depended on the nature of the
amine additives. Although their exact role has not been
clear, they would act as proton sources to inhibit the
alkyne oligomerization and as ligands to prevent an
aggregation of the reaction intermediates. In the latter
case, it is likely that a more active species such as
When 1,7-octadiyne (5a) was treated with the yttrium
catalyst and N(SiMe3)3 in toluene (0.7 M) at 100 °C for
(13) Evans reported that (C5Me5)2LnN(SiMe3)2 did not react with
phenylacetylene in toluene even at 100 °C, but the metathesis occurred
in THF. Evans, W. J.; Keyer, R. A.; Ziller, J. W. Organometallics 1993,
12, 2618-2633.
(14) When 1a was treated with PhNH2 (15 mol %) and Y[N(SiMe3)2]3
(5 mol %), no reaction commenced (see entry 4 in Table 1). The reaction
of 1h using Et3N (15 mol %) and the Y-silylamide (5 mol %) decreased
the yield of 2 g and 3g to 21 and 7% yields, respectively, with 49%
conversion (see entry 15).
(15) Trost, M. B.; Mathubara, S.; Caringi, J. J. J. Am. Chem. Soc.
1989, 111, 8745-8746.
(16) Nishibayashi, Y.; Yamanashi, M.; Wakiji, I.; Hidai, M. Angew.
Chem., Int. Ed. 2000, 39, 2909-2911.
(12) Molander, G. A.; Romero, J. A, C. Chem. Rev. 2002, 102, 2161-
2185
7262 J. Org. Chem., Vol. 70, No. 18, 2005

Silylamide-Catalyzed Selective Dimerization of Terminal Alkynes
TABLE 4. Examples of One-Pot Synthesis of
1-Phosphinyl-1,3-butadienes 10 by the Dimerization and
Subsequent Hydrophosphination
FIGURE 1. Two isomers derived from 1,7-octadiyne (5a).
entry
R
time (min)
yield of 10a (%)
TABLE 3. Examples for Double-Dimerization of
1
Ph (1a)
5
40
60
120
10
35
10a
94
r,ω-Diynes Leading to Bisenynes
2b
3
4-MeOC6H4 (1b)
4-MeC6H4 (1c)
4-BrC6H4 (1d)
4-FC6H4 (1e)
10b
10c
10d
10e
10f
81
81
4
80
5
92 (94)c
76
6d
2-MeC6H4 (1f)
a Isolated yield based on the phosphine. b Carried out at 100
°C. c The value in parentheses indicates an NMR yield. d 10 mol
% of the catalyst and additive were used.
balance of the reaction decreased with increasing con-
centration to 4.9 M due to the formation of oligomers
(entry 1). In contrast, 7a and 8a were isolated in 90%
combined yield at lower concentration (0.3 M) (entry 4).
Similarly, 1,8-nonadiyne (5b) was converted to the 16-
membered cyclic bisenynes 7b and 8b in 78% yield in
the dilute solution (entry 5). Interestingly, the ratio of 7
and 8 was always ca. 73:26 irrespective of the concentra-
tion and carbon-chain length. The reaction mode was
changed in the dimerization of 1,13-tetradecadiyne (5c),
which gave 13-membered monoenyne 9 in 61% yield
exclusively (entry 6).
a Isolated yield. The ratio was determined by NMR. b 10 mol %
of the catalyst and additive were used.
Last, we investigated one-pot synthesis of 1-phosphi-
nyl-1,3-butadienes from two moles of terminal alkyne and
one mole of phosphine in order to explore the synthetic
utility of the present dimerization. This idea evolved from
the fact that the rare-earth amide catalysts did not
decompose after completion of the alkyne dimerization
in the first step, and that they could catalyze hydrophos-
phination of the alkyne moiety of the thus-generated
enyne in the second step.10b It turned out that the reac-
tion worked successfully (Table 4). Thus, after generation
of (Z)-1,4-diphenylbut-1-en-3-yne (3a) from phenylacety-
lene (1a) with the yttrium catalyst and 4-chloroaniline
under the standard conditions, the mixture was subse-
quently treated with half-molar amounts of diphenylphos-
phine in the presence of the HMPA ligand (15 mol %) at
room temperature and then, oxidized with hydrogen
peroxide to give 1-diphenylphosphinyl-1,3-butadiene 10a
in 94% yield (entry 1). Similarly, various phosphinyl-
butadienes 10 were prepared in high yields via the head-
to-head dimers 3, starting from aromatic terminal alkynes.
In the reaction of 1b, the hydrophosphination in the
second step took place only at elevated temperature
probably because the chelate effect of the methoxy
substituent would retard the reaction.
All products 10 were obtained as single isomers whose
structures were determined unambiguously by X-ray
crystallographic analysis of 10c (see the Supporting
Information, Figure S2). The Ph2(O)P group was attached
to C(1) to form an (E)-double bond between C(1)-C(2),
in agreement with the previous results,10b whereas the
original (Z)-stereochemistry of C(3)-C(4) in 3c was
reversed to (E). The change of the stereochemistry of the
C(3)-C(4) double bond would be explained as shown in
Scheme 3. Initially, some yttrium amide species remained
20 h, a mixture of two dimeric products (76:24) was
obtained in 71% total yield, which was inseparable even
by HPLC. The mixture showed no signals assignable to
carbons and protons of terminal alkynes in the 13C and
1H NMR spectra, but two pairs of four olefinic protons
were observed in the region of 5.13-5.18 ppm, instead.
Therefore, the two compounds should be double-dimer-
ization products 7a and 8a (Figure 1). Considering their
structural symmetry, it is reasonable to assume that four
methylene protons A-D situated in linear relation for
7a, and four methylene protons a-d separated in two
parts for 8a, would appear independently. Thus, we
measured the H-H COSY spectra of the mixture to
determine their structures (see Supporting Information,
Figure S1). The major product exhibited four methylene
signals at ca. 1.5 (B), 1.8 (C), 2.2 (D), and 2.4 (A) ppm as
expected, wherein three COSY signals of A-B, B-C, and
C-D were clearly found, in addition to those of D-olefinic
protons. The minor product also showed three separate
signals at ca. 1.6 (c), 1.7 (b), and 2.3 (a) and one obscured
signal at 2.2 (d). However, only two COSY signals of a-b
and c-d were observed, other than those of d-olefinic
protons. On the basis of these results, the structure of
the major isomer was determined as 7a and the minor
as 8a.
The present reaction was found to be very sensitive to
the reaction conditions, particularly to the concentration
of the R,ω-diynes and the length of their methylene
chains, because the initial products 6 were able to react
further both intra- and intermolecularly to yield cyclic
bisenynes and oligomers, respectively (Table 3). The
reaction of 5a in 2.0 M solution gave a mixture of the
bisenynes 7a and 8a and mono-dimerization product 6a
in 30% and 53% yields, respectively (entry 2). Mass
J. Org. Chem, Vol. 70, No. 18, 2005 7263

Komeyama et al.
with ether (2 mL). GC yield was determined by using methyl
benzoate as an internal standard. The aqueous layer was
extracted with ether (30 mL). The combined organic layer was
washed with brine (30 mL), dried over MgSO4, filtered, and
concentrated in vacuo. The crude mixture gave 129 mg (90%)
of the dimer 3a by flash column chromatography on silica gel
with hexane eluent.
SCHEME 3
2-Butyloct-1-en-3-yne (2 g) [CAS Registry No. 5663-86-
5]: isolated in 85% yield as a yellow liquid; IR (neat) 3094,
2957, 2930, 2224 cm-1; MS m/z 164 (M+, 1), 149 (4), 122 (60),
107 (91), 93 (86), 79 (100); 1H NMR (CDCl3) δ 0.91 (3H, t, J )
7.3 Hz), 0.92 (3H, t, J ) 7.3 Hz), 1.25-1.55 (8H, m), 2.12 (2H,
t, J ) 7.4 Hz), 2.31 (2H, t, J ) 6.9 Hz), 5.12 (1H, s), 5.20 (1H,
s); 13C NMR (CDCl3) δ 10.8, 11.1, 16.2, 19.1, 19.2, 27.5, 28.1,
34.5, 78.2, 87.2, 116.5, 129.6.
2-Hexyldec-1-en-3-yne (2h) [CAS Registry No. 13343-
81-2]: isolated in 89% yield as a yellow liquid; IR (neat) 3427,
2928, 2858, 2212 cm-1; MS m/z 220 (M+, 10), 29 (100); 1H NMR
(CDCl3) δ 0.89 (3H, t, J ) 6.8 Hz), 0.90 (3H, t, J ) 6.9 Hz),
1.20-1.57 (16H, m), 2.11 (2H, t, J ) 7.5 Hz), 2.30 (2H, t, J )
7.0 Hz), 5.12 (1H, d, J ) 1.2 Hz), 5.20 (1H, d, J ) 1.4 Hz); 13
C
NMR (CDCl3) δ 14.0, 14.1, 19.3, 22.57, 22.62, 28.1, 28.5, 28.6,
28.8, 31.4, 31.7, 37.6, 81.0, 90.0, 119.2, 132.4.
after the dimerization reacted with Ph2PH to yield
phosphide complex C.10b syn-Addition of C to the alkyne
moiety of 3 affords dienyl yttrium (Z)-D. Because the (Z)-
stereochemistry causes severe steric repulsion, (Z)-D
would isomerize to more stable (E)-D via an allenic
intermediate E. Subsequent protonation with Ph2PH
affords the product 10 and phosphide C.
(Z)-1,4-Diphenylbut-1-en-3-yne (3a) [CAS Registry No.
13343-78-7]: isolated in 90% as a yellow liquid; IR (neat) 3061,
3020, 2189, 1489, 1447 cm-1; MS m/z 204 (M+, 59), 202 (100),
1
101 (50); H NMR (CDCl3) δ 5.93 (1H, d, J ) 11.8 Hz), 6.71
(1H, d, J ) 11.8 Hz), 7.29-7.41 (6H, m), 7.48-7.50 (2H, m),
7.93 (2H, d, J ) 7.5 Hz); 13C NMR (CDCl3) δ 88.2, 95.8, 107.4,
123.4, 128.27, 128.34, 128.4, 128.5, 128.7, 131.4, 136.5, 138.6.
(Z)-1,4-Di(4-anisyl)but-1-en-3-yne (3b) [CAS Registry
No. 500906-72-9]: isolated in 93% as a yellow liquid; IR (neat)
3005, 2957, 2930, 2835, 2185 cm-1; MS m/z 264 (M+, 100), 249
(38); 1H NMR (CDCl3) δ 3.80 (3H, s), 3.81 (3H, s), 5.77 (1H, d,
J ) 11.8 Hz), 6.58 (1H, d, J ) 11.8 Hz), 6.87 (2H, d, J ) 8.9
Hz), 6.89 (2H, d, J ) 8.9 Hz), 7.42 (2H, d, J ) 8.9 Hz), 7.88
(2H, d, J ) 8.7 Hz); 13C NMR (CDCl3) δ 55.22, 55.23, 87.4,
95.4, 105.1, 113.6, 114.0, 115.7, 129.7, 130.1, 132.8, 137.3,
159.5, 159.6.
Summary
Regio- and stereoselective dimerization of terminal
alkynes to produce conjugated enynes has been achieved
using rare-earth silylamide catalysts and amine addi-
tives. The yttrium catalyst is superior to larger metals
such as Sm and La. The amine additives play a crucial
role to control efficiency of the reaction and regiochem-
istry of the products. Oligomerization of the alkynes
predominates or competes with the dimerization in the
absence of the additives. As a rule, primary amines tend
to produce (Z)-head-to-head dimers preferentially and,
in contrast, tertiary amines bring about the head-to-tail
products. Thus, nearly complete formation of (Z)-head-
to-head dimers from aromatic terminal alkynes with
aniline derivatives and head-to-tail dimers from aliphatic
alkynes with N(SiMe2)3 is realized. When this reaction
is extended to R,ω-diynes, unprecedented double dimer-
ization takes place to afford cyclic bisenyne compounds,
depending on the length of the carbon chain and concen-
tration of the reaction mixture. Moreover, dimerization
of aromatic terminal alkynes, followed by hydrophosphi-
nation with diphenylphosphine enables highly efficient
synthesis of 1-phosphiny-1,3-butadienes in one-pot using
single rare-earth catalysts.
(Z)-1,4-Di(4-tolyl)but-1-en-3-yne (3c) [CAS Registry No.
189331-74-6]: isolated in 90% as a yellow solid; mp 61-63
°C; IR (KBr) 3026, 2920, 2856, 2361 cm-1; MS m/z 232 (M+,
1
100), 215 (58), 202 (67); H NMR (CDCl3) δ 2.37 (6H, s), 5.85
(1H, d, J ) 11.8 Hz), 6.65 (1H, d, J ) 11.8 Hz), 7.16 (2H, d, J
) 8.2 Hz), 7.19 (2H, d, J ) 8.2 Hz), 7.38 (2H, d, J ) 8.0 Hz),
7.83 (2H, d, J ) 8.2 Hz); 13C NMR (CDCl3) δ 21.4, 21.5, 87.9,
95.9, 106.5, 120.5, 128.7, 129.0, 129.2, 131.3, 133.9, 138.2,
138.4, one signal was obscured.
(Z)-1,4-Di(4-bromophenyl)but-1-en-3-yne (3d) [CAS Reg-
istry No. 500906-74-1]: isolated in 89% as a yellow liquid;
IR (CCl4) 2957, 2926, 2854, 2359, 2340 cm-1; MS m/z 364 (M+
1
+ 4, 5), 362 (M+ + 2, 12) (M+, 7), 202 (100); H NMR (CDCl3)
δ 5.92 (1H, d, J ) 11.8 Hz), 6.66 (1H, d, J ) 11.8 Hz), 7.32
(2H, d, J ) 8.4 Hz), 7.49 (2H, d, J ) 7.6 Hz), 7.51 (2H, d, J )
7.6 Hz), 7.76 (2H, d, J ) 8.5 Hz); 13C NMR (CDCl3) δ 88.9,
95.4, 107.9, 122.1, 122.5, 122.9, 130.1, 131.5, 131.8, 132.8,
135.3, 137.8.
(Z)-1,4-Di(4-fluorophenyl)but-1-en-3-yne (3e) [CAS Reg-
istry No. 557083-83-7]: isolated in 80% as a yellow liquid;
IR (CCl4) 3024, 2925, 2855, 2186 cm-1; MS m/z 240 (M+, 76),
1
239 (60), 238 (100); H NMR (CDCl3) δ 5.87 (1H, d, J ) 11.8
Experimental Section
Hz), 6.66 (1H, d, J ) 11.8 Hz), 7.03-7.09 (4H, m), 7.43-7.47
(2H, m), 7.87-7.91 (2H, m); 13C NMR (CDCl3) δ 87.6, 94.8,
106.8 (d, J ) 2.5 Hz), 115.2 (d, J ) 21.3 Hz), 115.7 (d, J )
23.0 Hz), 119.4 (d, J ) 3.3 Hz), 130.4 (d, J ) 8.2 Hz), 132.7 (d,
J ) 4.1 Hz), 133.3 (d, J ) 8.2 Hz), 137.4 (d, J ) 8.2 Hz), 162.5
(d, J ) 249.4 Hz), 162.6 (d, J ) 250.2 Hz).
General Procedure for the Dimerization of Terminal
Alkynes Catalyzed by Y[N(SiMe3)2]3 with Amine Addi-
tives. According to entry 1 in Table 2, Y[N(SiMe3)2]3 (39 mg,
0.07 mmol) and 4-ClC6H4NH2 (8.9 mg, 0.07 mmol) were placed
in a 20-mL Schlenk tube and dissolved in toluene (1.4 mL).
After the mixture was stirred for 1 h at room temperature,
phenylacetylene (1a) (146 mg, 1.4 mmol) was added. The
Schlenk tube was sealed, and stirring was continued for 17 h
at 100 °C. The reaction mixture was cooled, quenched with
H2O (2 mL) and saturated NH4Cl solution (1 mL), and diluted
(Z)-1,4-Di(2-tolyl)but-1-en-3-yne (3f) [CAS Registry No.
259090-89-6]: isolated in 75% as a yellow liquid; IR (neat)
3005, 2957, 2930, 2835, 2185 cm-1; MS m/z 232 (M+, 92), 215
(100), 202 (75), 115 (79); 1H NMR (CDCl3) δ 2.33 (3H, s), 2.43
(3H, s), 5.99 (1H, d, J ) 11.8 Hz), 6.86 (1H, d, J ) 11.8 Hz),
7264 J. Org. Chem., Vol. 70, No. 18, 2005

Silylamide-Catalyzed Selective Dimerization of Terminal Alkynes
7.12-7.22 (6H, m), 7.38 (1H, d, J ) 7.3 Hz), 8.25-8.27 (1H,
m); 13C NMR (CDCl3) δ 19.7, 20.7, 91.6, 93.9, 108.5, 123.2,
125.5, 128.2, 128.3, 129.4, 130.1, 132.1, 135.3, 136.4, 136.5,
140.2, two signals were obscured.
(Z)-Hexadec-7-en-9-yne (3h) [CAS Registry No. 13343-
80-1]: isolated in 43% as a yellow liquid; IR (neat) 3020,
2925, 2856, 1466 cm-1; MS m/z 220 (M+, 5), 29 (100); 1H
NMR (CDCl3) δ 0.86-0.90 (6H, m), 1.27-1.44 (14H, m), 1.48-
1.57 (2H, m), 2.26 (2H, q, J ) 7.2 Hz), 2.32 (2H, dt, J ) 1.8,
7.0 Hz), 5.42 (1H, dt, J ) 10.6, 1.8 Hz), 5.80 (1H, dt, J ) 10.6,
7.2 Hz); 13C NMR (CDCl3) δ 14.04, 14.08, 19.5, 22.58, 22.61,
28.6, 28.85, 28.86, 28.89, 30.0, 31.4, 31.7, 77.4, 94.3, 109.3,
142.6.
15.7, 9.9, 1.7 Hz), 6.83 (1H, br d, J ) 15.7 Hz), 7.08-7.10 (2H,
m), 7.20-7.30 (9H, m), 7.39-7.4 (4H, m), 7.48-7.53 (2H, m),
3
7.65-7.71 (4H, m); 13C NMR (CDCl3) δ 124.8 (d, JC-P
)
2
16.4 Hz), 127.1, 127.7, 128.2, 128.3 (d, JC-P ) 12.3 Hz),
128.6, 128.7, 130.3 (d, 3JC-P ) 4.1 Hz), 131.5 (d, 1JC-P ) 104.2
Hz), 131.7 (d, 4JC-P ) 2.5 Hz), 132.1 (d, 3JC-P ) 9.0 Hz), 135.2
1
2
(d, JC-P ) 95.6 Hz), 135.3 (d, JC-P ) 9.0 Hz), 136.2, 139.9,
143.5 (d, JC-P ) 10.6 Hz); 31P NMR (CDCl3) δ 28.64. Anal.
2
Calcd for C28H23OP: C, 82.74; H, 5.70. Found: C, 82.55; H,
5.45.
(E,E)-1,4-(4-Anisyl)-1-(diphenylphosphinyl)-1,3-butadi-
ene (10b): isolated in 81% as a yellow solid; mp 58-60 °C; IR
(Nujol) 1177 cm-1; 1H NMR (CDCl3) δ 3.781 (3H, s), 3.784 (3H,
s), 6.60 (1H, ddd, J ) 15.5, 9.9, 1.7 Hz), 6.67 (1H, br d, J )
15.5 Hz), 6.71 (2H, d, J ) 8.7 Hz), 6.72 (2H, d, J ) 8.7 Hz),
6.96 (2H, dd, J ) 8.8, 1.6 Hz), 7.05 (1H, dd, J ) 18.8, 9.9 Hz),
7.16 (2H, d, J ) 8.8 Hz), 7.31-7.36 (4H, m), 7.40-7.44 (2H,
m), 7.58-7.64 (4H, m); 13CNMR (CDCl3) δ 55.1, 55.2, 113.7,
3,10-Dimethylidenecyclotetradeca-1,8-diyne (7a) and
3,8-dimethylidenecyclotetradeca-1,9-diyne (8a): isolated
as a 72:28 mixture in 90% combined yield; IR (neat) 2928,
2858, 2218 cm-1; MS m/z (7a) 212 (M+, 14), 211 (4), 197 (4),
183 (24), 169 (45), 155 (58), 141 (84), 129 (61), 115 (49), 91
(82), 77 (68), 65 (46), 51 (59), 39 (100), (8a) 212 (M+, 2), 211
(8), 197 (20), 183 (29), 169 (60), 155 (83), 141 (100), 129 (60),
3
2
114.1, 112.4 (d, JC-P ) 9.8 Hz), 128.2 (d, JC-P ) 12.3 Hz),
128.3, 128.5, 129.1, 131.4 (d, 2JC-P ) 9.0 Hz), 131.6, 131.8 (d,
1JC-P ) 103.2 Hz), 132.1 (d, JC-P ) 16.4 Hz), 133.3 (d, JC-P
3
1
1
115 (47), 91 (77), 77 (67), 65 (51), 51 (54), 39 (99); H NMR
) 99.1 Hz), 139.2, 143.7 (d, 2JC-P ) 10.6 Hz), 159.0, 160.1; 31
P
(CDCl3) (7a) δ 1.46-1.53 (4H, m), 1.81-1.88 (4H, m), 2.18 (4H,
t, J ) 7.5 Hz), 2.38 (4H, t, J ) 6.1 Hz), 5.13 (2H, m), 5.18 (2H,
m), (8a) δ 1.61 (4H, m), 1.74 (4H, m), 2.18 (4H, m), 2.35 (4H,
m). 5.13 (2H, m), 5.19 (2H, m); 13C NMR (CDCl3, 67.8 Hz) (7a)
δ 19.0, 26.9, 27.3, 37.7, 81.2, 90.6, 119.3, 132.2, (8a) δ 19.1,
NMR (CDCl3) δ 28.99. Anal. Calcd for C30H27O3P: C, 77.24;
H, 5.83. Found: C, 77.13; H, 5.96.
(E,E)-1,4-(4-Tolyl)-1-(diphenylphosphinyl)-1,3-butadi-
ene (10c): isolated in 81% as a white solid; mp 177-182 °C;
IR (Nujol) 1167 cm-1 1H NMR (CDCl3) δ 2.30 (3H, s), 2.31
;
27.6, 27.8, 37.6, 81.2, 91.0, 119.7, 132.3. Anal. Calcd for
C16H20: C, 90.51; H, 9.49. Found: C, 90.54; H, 9.46.
(3H, s), 6.76-6.77 (2H, m), 6.98 (2H, d, J ) 8.3 Hz), 7.05 (2H,
d, J ) 8.3 Hz), 7.07 (2H, d, J ) 8.3 Hz), 7.16 (1H, ddd, J )
15.8, 6.5, 3.6 Hz), 7.19 (2H, d, J ) 8.3 Hz), 7.41-7.44 (4H, m),
7.48-7.50 (2H, m), 7.65-7.71 (4H, m); 13C NMR (CDCl3) δ
3,11-Dimethylidenecyclohexadeca-1,9-diyne (7b) and
3,9-dimethylenecyclohexadeca-1,10-diyne (8b): isolated
as a 70:30 mixture in 78% combined yield; a pale yellow liquid;
IR (neat) 2936, 2856, 2224 cm-1; MS m/z (7b) 240 (M+, 1), 239
(3), 225 (11), 211 (29), 197 (64), 183 (52), 169 (72), 155 (94),
141 (75), 129 (83), 91 (100), (8b) 240 (M+, 0.2), 239 (0.4), 211
(4), 197 (11), 183 (15), 169 (24), 141 (35), 129 (46), 91 (100);
1H NMR (CDCl3) signals of 7b and 8b were overlapped δ 1.17-
1.25 (8H, m), 1.48-1.69 (4H, m), 2.13-2.18 (4H, m), 2.32-
2.40 (4H, m), 5.12-5.13 (2H, m), 5.18-5.20 (2H, m); 13C NMR
(CDCl3) (7b) 19.4, 28.0, 28.2, 28.4, 37.4, 80.8, 90.4, 119.7, 132.2,
(8b) δ 18.6, 27.1, 27.4, 27.8, 28.3, 38.1, 81.2, 90.4, 119.8, 132.3.
Anal. Calcd for C18H24: C, 89.94; H, 10.06. Found: C, 89.75;
H, 10.25.
3-Methylidenecyclotridec-1-yne (9): isolated in 61% as
a colorless liquid; IR (neat) 2932, 2858, 2210 cm-1; MS m/z
190 (M+, 0.01), 147 (1), 133 (4), 119 (7), 105 (14), 93 (36), 79
(81), 67 (100); 1H NMR (CDCl3) δ 1.38 (10H, m), 1.52-1.62
(6H, m), 2.17 (2H, t, J ) 6.9 Hz), 2.33 (2H, t, J ) 5.5 Hz), 5.12
(1H, m), 5.18 (1H, m); 13C NMR (CDCl3) δ 19.2, 25.4, 25.6, 26.1,
26.2, 26.3, 26.9, 27.0, 36.7, 81.7, 91.1, 119.3, 132.8, one signal
was obscured. Anal. Calcd for C14H22: C, 88.35; H, 11.65.
Found: C, 88.54; H, 11.46.
21.2, 21.3, 123.6 (d, 3JC-P ) 17.2 Hz), 127.1, 128.3 (d, 2JC-P
)
11.4 Hz), 129.0, 129.4, 130.3 (d, 3JC-P ) 5.0 Hz), 131.6 (d, 4JC-P
1
3
) 2.5 Hz), 131.9 (d, JC-P ) 104.1 Hz), 132.2 (d, JC-P ) 9.9
Hz), 133.6, 134.6 (d, 1JC-P ) 98.4 Hz), 137.4, 138.9, 139.7, 143.6
(d, 2JC-P ) 10.6 Hz), one signal was obscured; 31P NMR (CDCl3)
δ 28.77. Anal. Calcd for C30H27OP: C, 82.93; H, 6.26. Found:
C, 82.76; H, 6.34.
(E,E)-1,4-(4-Bromodiphenyl)-1-(diphenylphosphinlyl)-
1,3-butadiene (10d): isolated in 80% as a yellow solid; mp
72-74 °C; IR (Nujol) 1177 cm-1; 1H NMR (CDCl3) δ 6.67 (1H,
ddd, J ) 15.9, 9.6, 1.7 Hz), 6.75 (1H, br d, J ) 15.9 Hz), 6.98-
7.00 (2H, m), 7.14 (1H, dd, J ) 18.6, 9.6 Hz), 7.15-7.18 (2H,
m), 7.38-7.47 (8H, m), 7.51-7.55 (2H, m), 7.65-7.70 (4H, m);
3
13C NMR (CDCl3) δ 122.2, 122.9, 124.3 (d, JC-P ) 16.3 Hz),
128.4 (d, 2JC-P ) 12.3 Hz), 128.5, 128.6, 129.8, 131.5 (d, 4JC-P
3
) 2.1 Hz), 131.9, 132.0, 132.1 (d, JC-P ) 9.0 Hz), 134.1 (d,
2JC-P ) 9.0 Hz), 134.96 (d, 5JC-P ) 1.6 Hz), 134.92 (d, 1JC-P
)
97.6 Hz), 139.1, 143.4 (d, 2JC-P ) 9.8 Hz); 31P NMR (CDCl3) δ
28.55. Anal. Calcd for C28H21Br2OP: C, 59.60; H, 3.75.
Found: C, 59.72; H, 3.68.
(E,E)-1,4-(4-Fluorodiphenyl)-1-(diphenylphosphinyl)-
1,3-butadiene (10e): isolated in 92% as a white solid; mp
General Procedure for One-Pot Synthesis of 1-Di-
phenylphosphinyl-1,3-butadienes 10. According to entry
1 in Table 4, after treatment of Y[N(SiMe3)2]3 (136 mg, 0.24
mmol) with 4-ClC6H4NH2 (26 mg, 0.25 mmol) in toluene at
room temperature for 1 h, 1a (507 mg, 5.0 mmol) was added
to the mixture and stirring was continued at 100 °C for 16 h.
The reaction mixture was cooled to room temperature, and
then HMPA (125µL, 0.72 mmol) and diphenylphosphine (466
mg, 2.5 mmol) were added. The mixture was stirred for 5 min
at room temperature with monitoring by GC. The reaction
mixture was quenched with saturated NH4Cl solution (3 mL),
diluted with ether (3 mL), and oxidized with 30% H2O2 solution
(2 mL) for 30 min at room temperature. The aqueous layer
was extracted with ether (30 mL). The combined organic layer
was washed with brine (30 mL), dried over MgSO4, filtered,
and concentrated in vacuo. The residue was chromatographed
on silica gel with 20% EtOAc/Hexane as an eluent to give 711
mg (94%) of 1-diphenylphosphinyl-1,3-butadieynes 10a.
56-58 °C; IR (Nujol) 1176 cm-1 1H NMR (CDCl3) δ 6.65
;
(1H, ddd, J ) 15.7, 10.6, 1.7 Hz), 6.78 (1H, d, J ) 15.7 Hz),
6.93-6.99 (4H, m), 7.05-7.09 (2H, m), 7.19 (1H, dd, J ) 18.5,
10.6 Hz), 7.25-7.28 (2H, m), 7.42-7.46 (4H, m), 7.51-7.53
(2H, m), 7.65-7.70 (4H, m); 13C NMR (CDCl3) δ 115.4 (d,
2
2JC-F ) 22.1 Hz), 115.8 (d, JC-F ) 21.3 Hz), 123.7 (d, J )
2
3
17.2 Hz), 128.4 (d, JC-P ) 11.5 Hz), 128.8 (d, JC-P ) 8.2
1
2
Hz), 130.7 (d, JC-P ) 104.1 Hz), 131.1 (dd, JC-P ) 8.6 Hz,
4JC-F ) 3.7 Hz), 131.9 (d, JC-P ) 2.5 Hz), 132.3 (d, JC-P
)
)
4
3
1
2
10.6 Hz), 133.8 (d, JC-P ) 98.4 Hz), 139.0, 143.7 (d, JC-P
10.6), 162.3 (d, 1JC-F ) 247.5 Hz), 163.0 (d, 1JC-F ) 250.0 Hz),
two signals were obscured; 31P NMR (CDCl3) δ 27.88. Anal.
Calcd for C28H21F2OP: C, 76.01; H, 4.78. Found: C, 76.21; H,
4.58.
(E,E)-1,4-(2-Tolyl)-1-(diphenylphosphinyl)-1,3-butadi-
ene (10f): isolated in 76% as a white solid; mp 144-146 °C;
(E,E)-1,4-Diphenyl-1-(diphenylphosphinyl)-1,3-butadi-
IR (Nujol) 1177 cm-1 1H NMR (CDCl3) δ 1.72 (3H, s), 2.35
;
ene (10a): isolated in 94% as a white solid; mp 137-139 °C;
(3H, s), 6.39 (1H, ddd, J ) 15.4, 11.0, 2.1 Hz), 6.76 (1H, d, J
) 7.6 Hz), 6.98-7.25 (8H, m), 7.29-7.36 (2H, m), 7.42-7.54
1
IR (Nujol) 1177 cm-1; H NMR (CDCl3) δ 6.77 (1H, ddd, J )
J. Org. Chem, Vol. 70, No. 18, 2005 7265

Komeyama et al.
(6H, m), 7.64 (1H, dd, J ) 18.0, 11.0 Hz), 7.69-7.77 (2H, m);
Acknowledgment. We are grateful to Dr. Yuushou
Nakayama for performing the X-ray analysis of com-
pound 10c.
3
13C NMR (CDCl3) δ 19.6, 19.7, 125.2 (d, JC-P ) 17.1), 125.5,
5
2
125.6, 126.0, 127.9 (d, JC-P ) 3.6 Hz), 128.4 (d, JC-P ) 12.1
3
Hz), 128.6, 129.5 (d, JC-P ) 3.7 Hz), 130.2, 130.5, 131.7 (d,
4JC-P ) 2.4 Hz), 132.3 (d, JC-P ) 9.8 Hz), 134.2 (d, JC-P
)
3
1
Supporting Information Available: General experimen-
tal details, H-H COSY spectra (7a and 8a), and X-ray
crystallographic data of 10c. This material is available free of
charge via the Internet at http://pubs.acs.org.
96.3 Hz), 134.3 (d, 2JC-P ) 8.5 Hz), 135.1, 137.5, 138.0, 138.1,
143.8 (d, JC-P ) 8.5 Hz), one signal was obscured; 31P NMR
2
(CDCl3) δ 26.33. Anal. Calcd for C30H27OP: C, 82.93; H, 6.26.
Found: C, 82.78; H, 6.38.
JO0509206
7266 J. Org. Chem., Vol. 70, No. 18, 2005