Enantiospecific synthesis of 1,3-disubstituted allenes by palladium-catalyzed coupling of propargylic compounds with arylboronic acids

Article abstract of DOI:10.1016/j.tet.2007.05.035

An enantiospecific coupling of propargylic esters and carbonates with arylboronic acids has been developed using a palladium catalyst. Optically active 1,3-disubstituted allenes were synthesized with high enantiomeric excesses by carrying out the reaction

Full text of DOI:10.1016/j.tet.2007.05.035

Tetrahedron 63 (2007) 6996–7002
Enantiospecific synthesis of 1,3-disubstituted allenes
by palladium-catalyzed coupling of propargylic
compounds with arylboronic acids
*
Masahiro Yoshida, Tatsuro Okada and Kozo Shishido
Graduate School of Pharmaceutical Sciences, The University of Tokushima, 1-78-1 Sho-machi, Tokushima 770-8505, Japan
Received 13 April 2007; revised 8 May 2007; accepted 9 May 2007
Available online 13 May 2007
Abstract—An enantiospecific coupling of propargylic esters and carbonates with arylboronic acids has been developed using a palladium
catalyst. Optically active 1,3-disubstituted allenes were synthesized with high enantiomeric excesses by carrying out the reactions under basic
aqueous conditions.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
various substituted allenes were synthesized, but in most
cases the enantiomeric excesses turned out to be modest.
We reported a direct coupling of propargylic alcohols with
arylboronic acids using a palladium catalyst, in which a prac-
tical and efficient synthesis of various substituted allenes has
been achieved.5c However, when an optically active propar-
gylic alcohol was used, the corresponding product was
nearly racemic. During the course of our studies on the enan-
tiospecific coupling with organoboron compounds, it be-
came clear that, when the propargylic carbonate was
employed, the chirality was successfully transferred to the
allenic axial chirality.5c Since we anticipated that the enan-
tiospecificity in this type of coupling would be influenced
by the propargylic leaving group, we set about examining
various ways to improve the reaction. Herein, we describe
a methodology for the enantiospecific synthesis of 1,3-
disubstituted allenes 3 by palladium-catalyzed coupling of
propargylic esters 1 with arylboronic acids 2 (Scheme 1),
in which various aryl-substituted allenes were synthesized
in high enantiomeric excess under basic aqueous conditions.
Functionalized allenes are versatile building blocks for
organic synthesis because of the inherent reactivity of their
axially chiral backbones.1 Most of the natural products con-
taining an allene moiety that have been isolated have axial
chirality.2 Consequently, much attention and extensive study
have been focused on the synthesis of optically active
allenes,1 with palladium-catalyzed couplings of propargylic
substrates being one of the most useful and efficient method-
ologies. In these couplings, substituted allenes having an
overall anti-substitution are normally produced via an
anti-SN20 attack of palladium on the propargylic substrates.
It has been reported that palladium complexes catalyze the
coupling of propargylic substrates with organozinc reagents3
yielding the substituted optically active allenes with high
enantiospecificities. However, these reactions usually have
to be conducted under anhydrous conditions.
Organoboron compounds are popular reagents in organic
synthesis owing to their stability, commercial availability,
and nontoxicity,4 and some propargylic couplings using
organoboron compounds have been reported.5 We reported
a coupling reaction of propargylic oxiranes with arylboronic
acids by palladium catalyst. The reactions can be carried out
in aqueous media to produce the aryl-substituted 2,3-
allenols with high anti-diastereoselectivity.5a Molander
developed a palladium-catalyzed synthesis of chiral ene-
allenes employing optically active propargylic substrates
with alkenyl trifluoroborates.5b Following his method,
H
X
H
cat. Pd(0)
R
H
R
*
*
H
1
+
ArB(OH)2
R
H
Ar
Pd
3
2
Scheme 1.
2. Results and discussion
The propargylic substrates 1a–g for the coupling reaction
were synthesized as follows (Scheme 2). (R)-1-Phenyl-2-
* Corresponding author. Tel./fax: +81 88 6337294; e-mail: yoshida@ph.
tokushima-u.ac.jp
0040–4020/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2007.05.035

M. Yoshida et al. / Tetrahedron 63 (2007) 6996–7002
6997
propyn-1-ol (4a) was subjected to esterification with the
chlorocarbonates 5a–c and 5e and the acid chlorides 5f
and 5g leading to the corresponding propargylic carbonates
1a–c and 1e and the esters 1f and 1g in high yields. Addition-
ally, the tert-butyl carbonate 1d was prepared from the reac-
tion of 4a with di-tert-butyl dicarbonate (5d) in 94% yield.
examined (Table 1). When methyl carbonate 1a (96% ee)
and 2a were subjected to the reaction with 10 mol % of
Pd(PPh3)4 in dioxane at 100 ꢀC for 10 min, the optically ac-
tive aryl-substituted allene 3a was produced in 76% yield
with 92% ee (entry 1).6 However, the enantiomeric excesses
decreased when ethyl, phenyl, tert-butyl and benzyl carbon-
ates 1b–e were employed (entries 2–5). Furthermore, the
nearly racemic 3a was obtained in low yields in the case
of the propargylic acetate 1f and the benzoate 1g (entries 6
and 7). These results suggested that improvement of the
reaction conditions would be essential to increase the enan-
tiomeric excesses of the coupling reactions.
O
ROCO
Ph
HO
Ph
g
R
Cl
5a-c, 5e-
DMAP, pyridine, 0 °C
H
H
4a
(96% ee)
1a-1c, 1e-g
1a: R = OMe 99%
1b: R = OEt 98%
1c: R = OPh 97%
1e: R = OBn 89%
1f: R = Me 76%
1g: R = Ph 78%
5a: R = OMe
5b: R = OEt
5c: R = OPh
5e: R = OBn
5f: R = Me
5g: R = Ph
t
Table 1. Initial attempts to synthesize the optically active allene 3a
H
10 mol%
Ph
X
Pd(PPh3)4
+
H
B(OH)2
Ph
dioxane, 100 ºC
10-20 min
BuO2CO
H
_
Boc2O 5d, DMAP
CH3CN, 0 °C, 94%
4a
Ph
1a 1g
2a
3a
H
1d
(96% ee)
Entry
X
Yield (%)
eea (%)
Scheme 2.
1
2
3
4
5
6
7
OCO2Me (1a)
OCO2Et (1b)
OCO2tPh (1c)
OCO2 Bu (1d)
OCO2Bn (1e)
OAc (1f)
76
81
61
87
81
27
12
92
28
39
12
8
We also prepared various substituted propargylic carbonates
1h–k (Scheme 3). Pentyl- and methyl-substituted substrates
1h and 1i were synthesized from the reactions of (S)-1-
octyn-3-ol (4h) and (S)-3-butyn-1-ol (4i) with benzyl chloro-
carbonate (5e). Propargylic alcohol 4h was subjected to the
Sonogashira coupling with iodobenzene to afford the
coupled product 6, which was transformed to the phenyl-
substituted substrate 1j. The TBS-substituted propargylic
alcohol 7, after being synthesized in three steps from 4a
by the selective introduction of the TBS group, was further
transformed to the corresponding benzyl carbonate 1k by
reaction with 5e.
3
0
OBz (1g)
a
Enantiomeric excess was determined by HPLC using a chiral column.
One possible explanation for the racemization of the re-
sulting allenes derived from propargylic esters 1f and 1g
might be that the attack of palladium proceeded in a stepwise
fashion via the achiral propargylic cation intermediate 9
(Scheme 4). Thus, these reactions produce the correspond-
ing carboxylic acids as co-products, which could promote
an SN10 attack of palladium (8 to 9) to afford the racemic
allenylpalladium. To overcome this problem, we examined
the reactions in the presence of base (Table 2). Although
KOH or Na2CO3 were ineffective (entries 2 and 3), the
enantiomeric excesses of the resulting allene 3a were
dramatically increased when Cs2CO3 or K3PO4 was used
(entries 4 and 5).7
O
HO
R
BnO2CO
R
BnO
Cl
5e
DMAP, pyridine
0 °C
H
H
1h: R = pentyl 69%
1i: R = Me 46%
4h: R = pentyl (98% ee)
4i: R = Me (99% ee)
PhI,
O
PdCl2(PPh3)2
HO
BnO
Cl
5e
CuI
Et3N, 99%
Ph
4h
DMAP, pyridine
0 °C, 53%
H
H+or :B(OH)2Ar
O
6
BnO2CO
Ph
Ph
H
O
H
1j
Ph
H
O
1) DHP, TsOH
_
8
9
2) BuLI, 78 °C;
HO
Ph
BnO
Cl
5e
TBSCl
3) TsOH, MeOH
3 steps 60%
Scheme 4.
4a
TBS
DMAP, pyridine
0 °C, 75%
H
7
It is known that Suzuki–Miyaura reactions often proceed
rapidly and efficiently in aqueous solvent.8,5a To examine
the effect of water on our coupling process, we next investi-
gated the reactions in aqueous solvent (Table 3). When prop-
argylic carbonate 1b was reacted with 2a in dioxane/H2O
mixed solvent, the enantiomeric excesses of the resulting al-
lene 3a were improved (entries 2–4). The best results were
obtained by carrying out the reaction in a 2:1 ratio of diox-
ane/H2O (89% ee in entry 3).
BnO2CO
Ph
TBS
H
1k
Scheme 3.
The couplings of the optically active propargylic substrates
1a–g with 2-methylphenylboronic acid (2a) were initially

6998
M. Yoshida et al. / Tetrahedron 63 (2007) 6996–7002
Table 2. Effects of base on the coupling of propargylic ester 1f with 2a
successfully transformed to the optically active 3a in the
presence of K3PO4 under aqueous conditions (entries 6
and 7). After several attempts, when the propargylic benzo-
ate 1e was subjected to the reaction with K3PO4 in dioxane/
H2O, 3a was produced in 93% yield with 94% ee (entry 8).
The reaction can be performed in the presence of 2 mol %
palladium catalyst without loss of reactivity (83% yield
with 94% ee, entry 10), and 3a is efficiently obtained even
when the catalyst loading is decreased to 1 mol % (69%
yield with 81% ee, entry 11).
H
10 mol%
Ph
AcO
Ph
Pd(PPh3)4
+
H
B(OH)2
base, dioxane
100 ºC, 15 min
H
1f
2a
3a
(96% ee)
Entry
Basea
Yield (%)
eeb (%)
1
2
3
4
5
None
KOH
Na2CO3
Cs2CO3
K3PO4
27
60
60
75
87
3
2
5
62
74
The reactions of the propargylic benzyl carbonate 1e with the
arylboronic acids 2b–g under optimized conditions are sum-
marized in Table 5. The corresponding substituted allenes
3b–g were obtained in good yields with high optical purities
from reactions with the various methyl- and methoxy-
substituted phenylboronic acids 2b–d (entries 1–3). Phenyl-
and 2-methylnaphthaleneboronic acids (2e and 2f) also
afforded 3e and 3f with high enantiomeric excesses (entries
4 and 5). In contrast, the optical purity was lowered when
4-acetylphenylboronic acid (2g) was employed (entry 6).
a
5 equiv of base was used.
Enantiomeric excess was determined by HPLC using a chiral column.
b
Table 3. Effects of water on the coupling of 1b with 2a
H
10 mol%
Ph
EtO2CO
Ph
Pd(PPh3)4
+
B(OH)2
H
solvent, 100 ºC
15 min
H
1b
2a
3a
Table 6 shows our attempts at using the propargylic carbon-
ates 1h–k having various substituents at the propargylic
position and alkyne terminus. When the pentyl- and
methyl-substituted substrates 1h and 1i were reacted with
2-methylphenylboronic acid (2a) and 1-naphthaleneboronic
acid (2h), the coupled allenes 3h and 3i were produced in
83% ee and 74% ee, respectively (entries 1 and 2). On the
other hand, the enantiomeric excesses of the corresponding
allenes 3j and 3k were lower in the reaction of 2a with 1j
and 1k, which have a substituent at the alkyne terminus
(entries 3 and 4). In the reaction of 1k, the propargylic arene
(96% ee)
Entry
Solvent
Yield (%)
eea (%)
1
2
3
4
Dioxane
81
71
71
36
28
51
89
68
Dioxane/H2O (3:1)
Dioxane/H2O (2/1)
Dioxane/H2O (1:1)
a
Enantiomeric excess was determined by HPLC using a chiral column.
Table 4 shows the results of the reactions of the propargylic
substrates 1a–g with 2a under optimized conditions. Under
aqueous conditions (dioxane/H2O¼2:1), the reactions of
the propargylic carbonates 1a–e successfully proceeded to
give the optically active 3a in good enantiomeric excesses
(entries 1–5). The propargylic esters 1f and 1g were also
Table 5. Reactions using various arylboronic acids 2b–g
BnO2CO
Ph
Ph
H
H
10 mol% Pd(PPh3)4
+
ArB(OH)2
5 eq. K3PO4
dioxane/H2O (2 : 1)
100 ºC, 3-20 min
Ar
H
_
_
2b 2g
3b 3g
eea (%)
92
1e (96% ee)
Table 4. Synthesis of chiral allene 3a under optimized conditions
Entry
1
ArB(OH)2
B(OH)2
Product
Yield (%)
H
10 mol%
Ph
X
Pd(PPh3)4
+
H
B(OH)2
3b
61
85
71
64
Ph
dioxane/H2O (2/1)
100 ºC, 4-20 min
H
2b
_
1a 1g
(96% ee)
OMe
2a
3a
2
3
4
3c
3d
3e
75
90
94
B(OH)2
2c
a
Entry
X
K3PO4
Yield (%)
eeb (%)
MeO
B(OH)2
1
2
3
4
5
6
7
8
OCO2Me (1a)
OCO2Et (1b)
OCO2Ph (1c)
ꢁ
ꢁ
ꢁ
ꢁ
ꢁ
+
+
+
+
+
69
71
61
73
64
73
82
93
85
83
69
93
89
91
93
87
86
88
94
94
94
81
2d
t
OCO2 Bu (1d)
B(OH)2
2e
OCO2Bn (1e)
OAc (1f)
OBz (1g)
OCO2Bn (1e)
OCO2Bn (1e)
OCO2Bn (1e)
OCO2Bn (1e)
9c
10d
11e
5
3f
99
50
86
66
B(OH)2
+
2f
a
5 equiv of K3PO4 was used.
b
c
d
e
Ac
B(OH)2
Enantiomeric excess was determined by HPLC using a chiral column.
5 mol % of Pd(PPh3)4 was used.
2 mol % of Pd(PPh3)4 was used.
6
3g
2g
a
1 mol % of Pd(PPh3)4 was used.
Enantiomeric excess was determined by HPLC chiral column.

M. Yoshida et al. / Tetrahedron 63 (2007) 6996–7002
Table 6. Reactions using various substituted propargylic carbonates 1h–ka
6999
4. Experimental section
Entry
Substrate
Productb
4.1. General
H
BnO2CO
All nonaqueous reactions were carried out under a positive
atmosphere of argon or nitrogen in dried glassware unless
otherwise indicated. Materials were obtained from commer-
cial suppliers and used without further purification except
when otherwise noted. Solvents were dried and distilled
according to standard protocols. The phrase ‘residue upon
workup’ refers to the residue obtained when the organic
layer was separated and dried over anhydrous MgSO4 and
the solvent was evaporated under reduced pressure.
1c
H
H
1h (98% ee)
3h 79%, 83% ee
Me
H
H
BnO2CO
Me
2d
H
1i (99% ee)
3i 75%, 74% ee
Ph
BnO2CO
Ph
4.2. General procedure for the preparation of propar-
gylic compounds: synthesis of propargylic carbonate 1e
3c,e
H
H
1j (98% ee)
3j 92%, 6% ee
To a stirred solution of (R)-1-phenyl-2-propyn-1-ol (4a)
(313 mg, 2.37 mmol, 96% ee) and pyridine (1.5 mL,
19.0 mmol) in CH2Cl2 (30 mL) was added dropwise benzyl
chloroformate (5e) (1.21 g, 7.11 mmol) at 0 ꢀC, and stirring
was continued for 2.5 h at the same temperature. The reac-
tion mixture was diluted with saturated aq NH4Cl and
extracted with AcOEt. The combined extracts were washed
with brine, and the residue upon workup was chromato-
graphed on silica gel with hexane/AcOEt (95:5 v/v) as eluent
to give propargylic carbonate 1e (562 mg, 89%) as a color-
less oil.
TBS
Ph
H
BnO2CO
Ph
TBS
+
4c,e
TBS
10 34%, 20% ee
H
Ph
H
1k (96% ee)
3k 60%, 38% ee
a
The reactions were carried out using 10 mol % of Pd(PPh3)4 and 5 equiv
of K3PO4 in dioxane/H2O (2:1) at 100 ꢀC for 5–10 min.
Enantiomeric excess was determined by HPLC chiral column.
2-Methylphenylboronic acid (2a) was used.
1-Naphthaleneboronic acid (2h) was used.
Absolute configurations of 3j, 3k, and 10 are not determined.
b
c
d
e
4.2.1. (R)-O-Methoxycarbonyl-1-phenyl-2-propyn-1-ol
(1a). Yield 99%; 96% ee; [a]2D9 ꢁ6.2 (c 14.4, CHCl3); IR
1
(neat) 3290, 2958, 1752, 1495, 789, 766 cmꢁ1; H NMR
10 was obtained in 34% yield with 20% ee as a by-product
(entry 4).5c The reason for the observed low enantiomeric
excesses is unclear, but it could be speculated that isomeri-
zation of the allenylpalladium occurred. It has been reported
that optically active allenylpalladium is rapidly racemized.9
We anticipated that the transmetallation of the allenylpalla-
dium with the arylboronic acids could be retarded by alkynyl
substitution, which promotes the racemization of the allenyl-
palladium in the coupling process (Scheme 5).
(400 MHz, CDCl3) d 7.56–7.25 (5H, m), 6.29 (1H, d,
J¼2.4 Hz), 3.81 (3H, s), 2.72 (1H, d, J¼2.4 Hz); 13C
NMR (100 MHz, CDCl3) d 154.9, 136.0, 129.4, 128.8,
128.8, 127.8, 127.8, 79.7, 76.7, 69.3, 55.1; MS m/z 190
(M+); HRMS m/z calcd for C11H10O3 190.0630 (M+), found
190.0638.
4.2.2. (R)-O-Ethoxycarbonyl-1-phenyl-2-propyn-1-ol
(1b). Yield 98%; 96% ee; colorless oil; [a]2D8 ꢁ5.78 (c
8.88, CHCl3); IR (neat) 3290, 1748 cmꢁ1 1H NMR
;
(400 MHz, CDCl3) d 7.57–7.38 (5H, m), 6.28 (1H, d,
J¼2.0 Hz), 4.24 (2H, q, J¼7.2 Hz), 2.71 (1H, d,
J¼2.0 Hz), 1.31 (3H, t, J¼7.2 Hz); 13C NMR (100 MHz,
CDCl3) d 154.1, 135.8, 129.2, 128.6, 128.6, 127.6, 127.6,
79.6, 76.3, 68.9, 64.4, 14.1; MS m/z 204 (M+); HRMS m/z
calcd for C12H12O3 204.0786 (M+), found 204.0771.
R'
R'
Ar
R
R
Pd+
H
H
ArB(OH)2
+
Pd+
R'
Ar
R'
R
R
H
H
4.2.3. (R)-O-Phenyloxycarbonyl-1-phenyl-2-propyn-1-ol
(1c). Yield 97%; 96% ee; colorless oil; [a]2D7 +13.5 (c 9.56,
Scheme 5.
1
CHCl3); IR (neat) 3306, 1758, 1594, 1494 cmꢁ1; H NMR
(400 MHz, CDCl3) d 7.62–7.18 (10H, m), 6.38 (1H, d,
J¼2.0 Hz), 2.78 (1H, d, J¼2.0 Hz); 13C NMR (100 MHz,
CDCl3) d 152.7, 151.0, 135.4, 129.5, 129.4, 129.4, 128.7,
128.7, 127.8, 127.8, 126.1, 120.8, 120.8, 79.2, 76.9, 70.0;
MS m/z 252 (M+); HRMS m/z calcd for C16H12O3
252.0786 (M+), found 262.0802.
3. Conclusion
In conclusion, the studies described above have resulted in
the synthesis of optically active 1,3-disubstituted allenes us-
ing palladium-catalyzed coupling of propargylic carbonates
and esters with arylboronic acids. High enantiospecificity
was achieved by conducting the reactions under optimized
basic aqueous conditions. The reaction can be carried out
under simple and mild reaction conditions to afford various
coupled optically active allenes conveniently.
4.2.4. (R)-O-tert-Butylcarbonyl-1-phenyl-2-propyn-1-ol
(1d). Yield 94%; 96% ee; [a]2D7 ꢁ3.08 (c 2.0, CHCl3); IR
(neat) 3290, 1743 cmꢁ1 1H NMR (400 MHz, CDCl3)
;
d 7.56–7.26 (5H, m), 6.24 (1H, d, J¼2.4 Hz), 2.69 (1H, d,

7000
M. Yoshida et al. / Tetrahedron 63 (2007) 6996–7002
J¼2.4 Hz), 1.49 (9H, s); 13C NMR (100 MHz, CDCl3)
d 152.4, 136.1, 129.0, 128.6, 128.6, 127.6, 127.6, 83.0,
79.9, 75.9, 68.1, 27.6, 27.6, 27.6; HRMS (ESI) m/z calcd
for C14H17O3 233.1178 (M++H), found 233.1184.
AcOEt (90:10 v/v) as eluent to give propargylic alcohol 6
(211 mg, 99%) as a colorless oil; [a]2D8 +3.91 (c 4.07,
1
CHCl3); IR (neat) 3337, 2930, 1599, 1490 cmꢁ1; H NMR
(400 MHz, CDCl3) d 7.45–7.29 (5H, m), 4.60 (1H, q, J¼
6.0 Hz), 1.85–1.33 (9H, m), 0.91 (3H, t, J¼6.8 Hz); 13C
NMR (100 MHz, CDCl3) d 131.6, 131.6, 128.3, 128.3,
128.2, 122.7, 90.3, 84.8, 63.0, 37.9, 31.4, 24.9, 22.5, 14.0;
HRMS (ESI) m/z calcd for C14H18O 203.1436 (M++H),
found 203.1434.
4.2.5. (R)-O-Benzyloxycarbonyl-1-phenyl-2-propyn-1-ol
(1e). Yield 89%; 96% ee; colorless oil; [a]2D8 ꢁ10.7 (c 2.64,
1
CHCl3); IR (neat) 3290, 1750 cmꢁ1; H NMR (400 MHz,
CDCl3) d 7.56–7.33 (10H, m), 6.29 (1H, d, J¼2.0 Hz), 5.21
(1H, d, J¼12.0 Hz), 5.17 (1H, d, J¼12.0 Hz), 2.71 (1H, d,
J¼2.0 Hz); 13C NMR (100 MHz, CDCl3) d 154.2, 135.8,
134.9, 129.3, 128.7, 128.7, 128.6, 128.6, 128.6, 128.3,
128.3, 127.7, 127.7, 79.6, 76.5, 70.1, 69.4; HRMS (ESI) m/z
calcd for C17H15O3 267.1022 (M++H), found 267.1021.
4.2.11. (S)-O-Benzyloxycarbonyl-1-phenyl-1-octyn-3-ol
(1j). Yield 53%; 98% ee; colorless oil; [a]2D9 ꢁ56.6 (c
1
1.95, CHCl3); IR (neat) 2955, 1748, 1599, 1491 cmꢁ1; H
NMR (400 MHz, CDCl3) d 7.44–7.25 (10H, m), 5.46 (1H,
t, J¼6.4 Hz), 5.20 (2H, s), 1.93–1.31 (8H, m), 0.90 (3H, t,
J¼7.2 Hz); 13C NMR (100 MHz, CDCl3) d 154.4, 135.2,
131.9, 131.9, 128.6, 128.6, 128.6, 128.5, 128.5, 128.3, 128.2,
128.2, 122.2, 86.2, 85.9, 69.8, 68.9, 34.9, 31.3, 24.6, 22.5,
13.9; HRMS (ESI) m/z calcd for C22H25O3 337.1804
(M++H), found 337.1805.
4.2.6. (R)-1-Acetoxy-1-phenyl-2-propyne (1f). Yield 76%;
96% ee; [a]2D7 +4.3 (c 15.0, CHCl3); IR (neat) 3289, 1742,
1
1495 cmꢁ1; H NMR (400 MHz, CDCl3) d 7.55–7.26 (5H,
m), 6.45 (1H, d, J¼2.4 Hz), 2.65 (1H, d), 2.11 (3H, s); 13C
NMR (100 MHz, CDCl3) d 170.0, 136.4, 129.1, 128.7,
128.7, 127.7, 127.7, 80.2, 75.3, 65.3, 21.0; HRMS (ESI)
m/z calcd for C11H11O2 175.0759 (M++H), found 175.0759.
4.2.12. (S)-3-tert-Butyldimethylsilyl-1-phenyl-2-propyn-
1-ol (7). To a stirred solution of (R)-1-phenyl-2-propyn-1-
ol (1.07 g, 8.10 mmol, 96% ee) and 3,4-dihydro-2H-pyran
(2.5 mL, 27 mmol) in CH2Cl2 (100 mL) was added p-tolue-
nesulfonic acid (200 mg, 1.05 mmol) at rt, and stirring was
continued for 1 h at the same temperature. The reaction mix-
ture was quenched with saturated aq NaHCO3 and extracted
with AcOEt. The combined extracts were washed with brine.
The residue upon workup was chromatographed on silica gel
with hexane/AcOEt (95:5 v/v) as eluent to give THP ether as
a colorless oil. To a stirred solution of the resulting THP
ether in THF (60 mL) was added dropwise n-BuLi (2.18 M)
(5.0 mL, 10.9 mmol) at ꢁ78 ꢀC, and stirring was continued
for 1 h at the same temperature. To the stirred solution was
added dropwise tert-butyldimethylsilyl chloride (1.38 g,
9.15 mmol) in THF (15 mL); stirring was continued for
1 h at the same temperature and for 1 h at rt. The reaction
mixture was quenched with saturated aq NH4Cl and ex-
tracted with hexane. The combined extracts were washed
with brine. To a stirred solution of the residue upon workup
in MeOH (200 mL) was added p-toluenesulfonic acid
(77.0 mg, 0.405 mmol) at rt, and stirring was continued for
10 h at the same temperature. The reaction mixture was
quenched with saturated aq NaHCO3 and extracted with
AcOEt. The combined extracts were washed with brine,
and the residue upon workup was chromatographed on silica
gel with hexane/AcOEt (97:3 v/v) as eluent to give propar-
gylic alcohol 7 (1.20 g, three steps 60%) as a colorless oil;
[a]2D6 ꢁ16.6 (c 10.7, CHCl3); IR (neat) 3367, 2954, 2929,
1603, 1494 cmꢁ1; 1H NMR (400 MHz, CDCl3) d 7.57 (2H,
d, J¼7.6 Hz), 7.55–7.33 (3H, m), 5.47 (1H, d, J¼6.4 Hz),
2.13 (1H, d, J¼6.4 Hz), 0.95 (9H, s), 0.15 (3H, s), 0.13
(3H, s); 13C NMR (100 MHz, CDCl3) d 140.4, 128.5, 128.5,
128.3, 126.7, 126.7, 105.7, 89.9, 65.0, 26.0, 26.0, 26.0, 16.5,
ꢁ4.7, ꢁ4.7; HRMS (ESI) m/z calcd for C15H23OSi 247.1518
(M++H), found 247.1518.
4.2.7. (R)-1-Benzoxy-1-phenyl-2-propyne (1g). Yield
78%; 96% ee; [a]2D7 ꢁ21.4 (c 3.74, CHCl3); IR (neat)
3292, 1722, 1601, 1494 cmꢁ1
;
1H NMR (400 MHz,
CDCl3) d 8.08 (2H, d, J¼8.0 Hz), 7.64–7.26 (8H, m), 6.70
(1H, d, J¼2.0 Hz), 2.69 (1H, d, J¼2.0 Hz); 13C NMR
(100 MHz, CDCl3) d 165.3, 136.5, 133.3, 129.9, 129.9,
129.5, 129.0, 128.7, 128.7, 128.4, 128.4, 127.6, 127.6,
80.2, 75.6, 65.8; MS m/z 236 (M+); HRMS m/z calcd for
C16H12O2 236.0837 (M+), found 236.0840.
4.2.8. (S)-O-Benzyloxycarbonyl-1-octyn-3-ol (1h). Yield
69%; 98% ee; colorless oil; [a]2D7 ꢁ51.2 (c 2.28, CHCl3); IR
(neat) 3293, 2956, 1749 cmꢁ1; 1H NMR (400 MHz, CDCl3)
d 7.40–7.33 (5H, m), 5.21 (1H, td, J¼6.8 and 2.0 Hz), 5.19
(2H, s), 2.51 (1H, d, J¼2.0 Hz), 1.85–1.78 (2H, m), 1.46
(2H, quint, J¼7.2 Hz), 1.33–1.28 (4H, m), 0.89 (3H, t,
J¼7.2 Hz); 13C NMR (100 MHz, CDCl3) d 154.1, 134.9,
128.4, 128.4, 128.3, 128.1, 128.1, 80.4, 74.4, 69.6, 67.7,
34.4, 31.0, 24.2, 22.2, 13.7; HRMS (ESI) m/z calcd for
C16H20O3Na 283.1310 (M++Na), found 283.1310.
4.2.9. (S)-O-Benzyloxycarbonyl-3-butyn-1-ol (1i). Yield
46%; 99% ee; colorless oil; [a]2D8 ꢁ63.2 (c 11.8, CHCl3);
1
IR (neat) 3293, 1749 cmꢁ1; H NMR (400 MHz, CDCl3)
d 7.39–7.26 (5H, m), 5.32 (1H, qd, J¼6.8 and 2.0 Hz),
5.21 (1H, d, J¼12.4 Hz), 5.17 (1H, d, J¼12.4 Hz), 2.52 (1H,
d, J¼2.0 Hz), 1.56 (3H, d, J¼6.8 Hz); 13C NMR (100 MHz,
CDCl3) d 154.1, 134.9, 128.5, 128.5, 128.5, 128.3, 128.3,
81.3, 73.8, 69.8, 64.0, 21.1; HRMS (ESI) m/z calcd for
C12H13O3 205.0865 (M++H), found 205.0865.
4.2.10. (S)-1-Phenyl-1-octyn-3-ol (6). To a stirred solution
of (S)-1-octyn-3-ol (4h) (133 mg, 1.05 mmol, 98% ee) in
Et3N (15 mL) were added iodobenzene (701 mg,
3.44 mmol), CuI (26.0 mg, 0.137 mmol), and PdCl2(PPh3)2
(48.2 mg, 0.0687 mmol) at rt, and stirring was continued for
3 h at the same temperature. The reaction mixture was di-
luted with water and extracted with AcOEt. The combined
extracts were washed with brine, and the residue upon
workup was chromatographed on silica gel with hexane/
4.2.13. (S)-O-Benzyloxycarbonyl-3-tert-butyldimethyl-
silyl-1-phenyl-2-propyn-3-ol (1k). Yield 75%; 96% ee; col-
orless oil; [a]3D0 ꢁ19.8 (c 5.0, CHCl3); IR (neat) 2953, 2929,
1748 cmꢁ1; 1H NMR (400 MHz, CDCl3) d 7.56–7.33 (10H,
m), 6.31 (1H, s), 5.21 (1H, d, J¼12.0 Hz), 5.14 (1H, d,

M. Yoshida et al. / Tetrahedron 63 (2007) 6996–7002
7001
J¼12.0 Hz), 0.92 (9H, s), 0.14 (6H, s); 13C NMR (100 MHz,
CDCl3) d 154.2, 136.3, 135.0, 129.1, 128.6, 128.6, 128.5,
128.5, 128.5, 128.3, 128.3, 127.9, 127.9, 101.2,
92.1, 70.1, 69.9, 26.0, 26.0, 26.0, 16.5, ꢁ4.9, ꢁ4.9; HRMS
(ESI) m/z calcd for C23H29O3Si 381.1886 (M++H), found
381.1879.
hexane, 0.5 mL/min, l¼254 nm, retention times 10.4 min
(R) and 12.4 min (S)]; IR (neat) 2957, 1934, 1606, 1509,
1494, 1459 cmꢁ1 1H NMR (400 MHz, CDCl3) d 7.36–
;
7.21 (7H, m), 6.86 (2H, dt, J¼8.8 and 2.5 Hz), 6.56 (2H,
s), 3.80 (3H, s); 13C NMR (100 MHz, CDCl3) d 207.2,
159.1, 133.9, 128.7, 128.7, 128.1, 128.1, 127.2, 126.9,
126.9, 125.8, 114.2, 114.3, 98.3, 97.8, 55.3; HRMS (ESI)
m/z calcd for C16H15O 223.1123 (M++H), found 223.1114.
4.3. General procedure for the palladium-catalyzed
reaction of propargylic compounds with arylboronic
acids: reaction of 1e with 2a
4.3.5. (R)-1,3-Diphenylpropadiene (3e). Yield 64%, 94%
ee; colorless crystals; mp 48–50 ꢀC; [a]D29 ꢁ866.9 (c 0.59,
CHCl3); enantiomeric excess was determined by HPLC
To a stirred solution of propargylic carbonate 1e (32.0 mg,
0.120 mmol) in 1,4-dioxane (0.8 mL) and H2O (0.4 mL)
were added 2-methylphenylboronic acid (2a) (32.6 mg,
0.240 mmol), K3PO4 (127 mg, 0.60 mmol), and Pd(PPh3)4
(13.9 mg, 0.012 mmol) at rt, and stirring was continued for
4 min at 100 ꢀC. The reaction mixture was filtered through
a small amount of silica gel and concentrated. The residue
was chromatographed on silica gel with hexane as eluent
to give allene 3a (23.0 mg, 93%, 94% ee) as a colorless oil.
i
analysis [CHIRALCEL OD-H column, 1% PrOH/hexane,
0.5 mL/min, l¼254 nm, retention times 10.2 min (R) and
13.6 min (S)]; IR (abs KBr) 3013, 1937, 1597, 1493 cmꢁ1
;
1H NMR (400 MHz, CDCl3) d 7.37–7.21 (10H, m), 6.60
(2H, s); 13C NMR (100 MHz, CDCl3) d 207.8, 133.6,
133.6, 128.7, 128.7, 128.7, 128.7, 127.3, 127.3, 127.0,
127.0, 127.0, 127.0, 98.4, 98.4; MS m/z 192 (M+); HRMS
m/z calcd for C15H12 192.0939 (M+), found 192.0943.
4.3.1. (R)-1-(2-Methylphenyl)-3-phenylpropadiene (3a).
Yield 93%; 94% ee; colorless oil; [a]2D6 ꢁ660.3 (c 2.1,
CHCl3); enantiomeric excess was determined by HPLC anal-
ysis [CHIRALCEL OJ-H column, 100% hexane, 0.5 mL/
min, l¼254 nm, retention times 16.8 min (R) and 20.0 min
4.3.6. (R)-1-(2-Methylnaphthyl)-3-phenylpropadiene
(3f). Yield 99%; 86% ee; colorless oil; [a]2D7 ꢁ538.4 (c
1.3, CHCl3); enantiomeric excess was determined by
HPLC analysis [CHIRALCEL OD-H column, 100% hex-
ane, 1.2 mL/min, l¼254 nm, retention times 44.5 min (S)
(S)]; IR (neat) 3026, 1935, 1598, 1492, 1455 cmꢁ1
;
1H
and 49.5 min (R)]; IR (neat) 3051, 1940, 1597, 1495 cmꢁ1
;
NMR (400 MHz, CDCl3) d 7.41–7.12 (9H, m), 6.78 (1H, d,
J¼6.8 Hz), 6.56 (1H, d, J¼6.8 Hz), 2.42 (3H, s); 13C NMR
(100 MHz, CDCl3) d 208.4, 135.3, 133.9, 131.9, 130.6,
128.7, 128.7, 127.6, 127.2, 127.2, 126.9, 126.9, 126.2,
97.6, 95.9, 20.0; MS m/z 206 (M+); HRMS m/z calcd for
C16H14 206.1096 (M+), found 206.1077.
1H NMR (400 MHz, CDCl3) d 8.30 (1H, d, J¼8.0 Hz),
7.80 (1H, d, J¼8.0 Hz), 8.30 (1H, d, J¼8.0 Hz), 7.69 (1H,
d, J¼8.0 Hz), 7.48–7.22 (7H, m), 7.10 (1H, d, J¼6.8 Hz),
6.47 (1H, d, J¼6.8 Hz), 2.58 (3H, s); 13C NMR (100 MHz,
CDCl3) d 208.3, 134.2, 134.0, 132.4, 131.8, 129.3, 128.7,
128.7, 128.3, 127.6, 127.4, 127.1, 127.1, 127.1, 126.2,
124.9, 124.5, 95.4, 92.9, 21.5; MS m/z 256 (M+); HRMS
m/z calcd for C20H16 256.1252 (M+), found 256.1255.
4.3.2. (R)-1-(4-Methylphenyl)-3-phenylpropadiene (3b).
Yield 61%; 92% ee; colorless oil; [a]2D9 ꢁ475.8 (c 1.2,
CHCl3); enantiomeric excess was determined by HPLC anal-
ysis [CHIRALCEL OD-H column, 1% iPrOH/hexane,
0.5 mL/min, l¼254 nm, retention times 9.74 min (R) and
4.3.7. (R)-1-(4-Acetylphenyl)-3-phenylpropadiene (3g).
Yield 50%; 66% ee; colorless oil; [a]3D0 ꢁ359.7 (c 0.72,
CHCl3); enantiomeric excess was determined by HPLC
1
i
14.8 min (S)]; IR (neat) 3023, 1935, 1598, 1492 cmꢁ1; H
analysis [CHIRALCEL OD-H column, 1% PrOH/hexane,
0.5 mL/min, l¼254 nm, retention times 15.3 min (R) and
NMR (400 MHz, CDCl3) d 7.35–7.11 (9H, m), 6.57 (2H,
s), 2.33 (3H, s); 13C NMR (100 MHz, CDCl3) d 207.6,
137.2, 133.8, 130.6, 129.5, 129.5, 128.7, 128.7, 127.2, 127.2,
127.0, 126.9, 126.9, 98.3, 98.2, 21.2; MS m/z 206 (M+);
HRMS m/z calcd for C16H14 206.1096 (M+), found 206.1085.
1
17.1 min (S)]; IR (neat) 3019, 1935, 1679, 1602 cmꢁ1; H
NMR (400 MHz, CDCl3) d 7.91 (2H, d, J¼8.4 Hz), 7.43
(2H, d, J¼8.4 Hz), 7.35–7.33 (5H, m), 6.66 (1H, d, J¼
2.4 Hz), 6.63 (1H, d, J¼2.4 Hz), 2.59 (3H, s); 13C NMR
(100 MHz, CDCl3) d 209.1, 197.4, 138.8, 135.9, 132.8,
128.9, 128.9, 128.8, 128.8, 127.6, 127.1, 127.1, 127.0, 127.0,
98.4, 97.9, 26.5; MS m/z 234 (M+); HRMS m/z calcd for
C17H14O 234.1045 (M+), found 234.1034.
4.3.3. (R)-1-(2-Methoxyphenyl)-3-phenylpropadiene
(3c). Yield 85%; 75% ee; colorless oil; [a]2D8 ꢁ346.8 (c
1.9, CHCl3); enantiomeric excess was determined by HPLC
i
analysis [CHIRALCEL OD-H column, 5% PrOH/hexane,
0.5 mL/min, l¼254 nm, retention times 9.2 min (R) and
4.3.8. (R)-1-(2-Methylphenyl)-1,2-octadiene (3h). Yield
79%; 83% ee; colorless oil; [a]2D2 ꢁ190.0 (c 0.49, CHCl3);
enantiomeric excess was determined by HPLC analysis
[CHIRALCEL OD-H column, 100% hexane, 0.5 mL/min,
l¼254 nm, retention times 12.3 min (R) and 14.2 min (S)];
1
12.4 min (S)]; IR (neat) 1935, 1596, 1493 cmꢁ1; H NMR
(400 MHz, CDCl3) d 7.41–7.18 (7H, m), 6.99 (1H, d,
J¼6.8 Hz), 6.91–6.88 (2H, m), 6.56 (1H, d, J¼6.8 Hz), 3.87
(3H, s); 13C NMR (100 MHz, CDCl3) d 208.3, 156.2, 134.0,
128.7, 128.7, 128.4, 128.0, 127.0, 126.9, 126.9, 122.0,
120.8, 111.1, 97.7, 92.4, 55.6; MS m/z 222 (M+); HRMS
m/z calcd for C16H14O 222.1045 (M+), found 222.1036.
1
IR (neat) 2926, 1947 cmꢁ1; H NMR (400 MHz, CDCl3)
d 7.37 (1H, d, J¼7.6 Hz), 7.16–7.07 (3H, m), 6.23 (1H, dt,
J¼6.8 and 9.2 Hz), 5.52 (1H, q, J¼6.8 Hz), 2.36 (3H, s),
2.12 (2H, m), 1.49 (2H, quint, J¼7.2 Hz), 1.36–1.32 (4H,
m), 0.89 (3H, t, J¼7.2 Hz); 13C NMR (100 MHz, CDCl3)
d 205.8, 134.8, 133.3, 130.4, 127.0, 126.5, 126.0, 94.2,
91.7, 31.4, 28.9, 28.8, 22.5, 19.8, 14.1; MS m/z 200 (M+);
HRMS m/z calcd for C15H20 200.1565 (M+), found 200.1572.
4.3.4. (R)-1-(4-Methoxyphenyl)-3-phenylpropadiene
(3d). Yield 71%; 90% ee; colorless oil; [a]2D9 ꢁ494.0 (c
1.2, CHCl3); enantiomeric excess was determined by
i
HPLC analysis [CHIRALCEL OD-H column, 5% PrOH/

7002
M. Yoshida et al. / Tetrahedron 63 (2007) 6996–7002
4.3.9. (R)-1-Naphthyl-1,2-propadiene (3i). Yield 75%;
74% ee; colorless oil; [a]2D2 ꢁ53.4 (c 0.16, CHCl3); enantio-
meric excess was determined by HPLC analysis [CHIRAL-
CEL OB-H column, 100% hexane, 0.3 mL/min, l¼254 nm,
retention times 24.2 min (S) and 25.4 min (R)]; IR (neat)
Foundation, and Astellas Foundation for Research on
Medicinal Resources.
References and notes
1947, 1591, 1509 cmꢁ1 1H NMR (400 MHz, CDCl3)
;
d 8.23 (1H, d, J¼8.0 Hz), 7.85 (1H, d, J¼7.2 Hz), 7.73
(1H, d, J¼8.0 Hz), 7.72–7.4 (4H, m), 6.81 (1H, dq, J¼3.2
and 7.2 Hz), 5.58 (1H, quint, J¼7.2 Hz), 1.85 (3H, dd,
J¼3.2 and 7.2 Hz); 13C NMR (100 MHz, CDCl3) d 207.5,
133.9, 131.2, 130.8, 128.6, 127.2, 125.9, 125.6, 125.6,
125.2, 123.6, 90.6, 88.5, 14.2; MS m/z 180 (M+); HRMS
m/z calcd for C14H12 180.0939 (M+), found 180.0941.
1. For selected reviews, see: (a) Marshall, J. A. Chem. Rev. 2000,
100, 3163; (b) Zimmer, R.; Dinesh, C. U.; Nandanan, E.;
Khan, F. A. Chem. Rev. 2000, 100, 3067; (c) Ma, S. Acc.
Chem. Res. 2003, 36, 701; (d) Hashmi, A. S. K. Angew.
€
Chem., Int. Ed. 2000, 39, 3590; (e) Hoffmann-Roder, A.;
Krause, N. Angew. Chem., Int. Ed. 2002, 41, 2933; (f) Krause,
€
N.; Hoffmann-Roder, A.; Canisius, J. Synthesis 2002, 1759;
€
(g) Hoffmann-Roder, A.; Krause, N. Angew. Chem., Int. Ed.
4.3.10. 1-(2-Methylphenyl)-1-phenyl-1,2-octadiene (3j).
Yield 92%; 6% ee; colorless oil; [a]2D5 +7.48 (c 1.64,
CHCl3); enantiomeric excess was determined by HPLC anal-
ysis [CHIRALCEL OF column, 100% hexane, 0.2 mL/min,
l¼254 nm, retention times 26.4 min (R) and 28.4 min (S)];
2004, 43, 1196.
2. (a) Krause, N.; Hoffmann-Roder, A. Allenic Natural Products
€
and Pharmaceuticals. In Modern Allene Chemistry; Krause,
N., Hashmi, A. S. K., Eds.; Wiley-VCH: Weinheim, 2004;
p 997; (b) Landor, S. R. Naturally Occurring Allenes. In The
Chemistry of the Allenes; Landor, S. R., Ed.; Academic:
London, 1982; p 679; (c) Claesson, A. Biologically Active
Allenes. In The Chemistry of the Allenes; Landor, S. R., Ed.;
Academic: London, 1982; p 709; (d) Robinson, C. H.; Covey,
D. F. Biological Formation and Reactions. In The Chemistry of
Ketenes, Allenes and Related Compounds; Patai, S., Ed.;
Wiley: Chichester, UK, 1980; p 451.
;
IR (neat) 2955, 2926, 1945, 1491 cmꢁ1 1H NMR
(400 MHz, CDCl3) d 7.29–7.16 (9H, m), 5.60 (1H, t,
J¼6.6 Hz), 2.20 (3H, s), 2.16 (2H, td, J¼8.0 and 6.6 Hz),
1.54–1.26 (6H, m), 0.86 (3H, t, J¼6.8 Hz); 13C NMR
(100 MHz, CDCl3) d 203.9, 137.4, 136.8, 136.5, 130.3,
130.2, 128.3, 128.3, 127.4, 126.5, 126.5, 126.4, 125.9, 125.5,
107.7, 94.0, 31.4, 28.9, 28.8, 22.5, 20.1, 14.0; HRMS (ESI)
m/z calcd for C21H24 277.1956 (M++H), found 277.1954.
3. (a) Elsevier, C. J.; Stehouwer, P. M.; Westmijze, H.; Vermeer, P.
J. Org. Chem. 1983, 48, 1103; (b) Dixneuf, P. H.; Guyot, T.;
Ness, M. D.; Roberts, S. M. Chem. Commun. 1997, 2083; (c)
Konno, T.; Tanikawa, M.; Ishihara, T.; Yamanaka, H. Chem.
Lett. 2000, 1360; (d) Elsevier, C. J.; Kleijn, H.; Boersma, J.;
Vermeer, P. Organometallics 1986, 5, 716; (e) Elsevier, C. J.;
Mooiweer, H. H.; Kleijn, H.; Vermeer, P. Tetrahedron Lett.
1984, 25, 5571.
4. (a) Cragg, G. M. Organoboranes in Organic Synthesis; Marcel
Decker: New York, NY, 1973; (b) Brown, H. C. Organic
Syntheses via Boranes; Wiley-Interscience: New York, NY,
1975; (c) Zaidlewicz, M.; Brown, H. C. Organic Syntheses via
Boranes; Aldrich Chemical: Milwaukee, 2001; (d) Roush,
W. R. Comprehensive Organic Synthesis; Trost, B. M.,
Fleming, I., Heathcock, C. H., Eds.; Pergamon: Oxford, 1991;
Vol. 2, p 1; (e) Matteson, D. S. Stereodirected Synthesis with
Organoboranes; Springer: Berlin, 1995; (f) Yamamoto, Y.;
Asao, N. Chem. Rev. 1993, 93, 2207; (g) Suzuki, A. Metal-
Catalyzed Cross-Coupling Reactions; Diederich, F., Stang,
P. J., Eds.; VCH: Weinheim, 1998; p 49; (h) Miyaura, N.;
Suzuki, A. Chem. Rev. 1995, 95, 2457.
4.3.11. 1-(2-Methylphenyl)-1-tert-butyldimethylsilyl-3-
phenylpropadiene (3k). Yield 60%; 38% ee; colorless oil;
[a]2D7 ꢁ13.9 (c 0.7, CHCl3); enantiomeric excess was deter-
mined by HPLC analysis [CHIRALCEL OD-H column,
100% hexane, 0.3 mL/min, l¼254 nm, retention times
18.1 min (R) and 19.0 min (S)]; IR (neat) 2955, 2927,
1
1920 cmꢁ1; H NMR (400 MHz, CDCl3) d 7.28–7.11 (9H,
m), 5.96 (1H, s), 2.35 (3H, s), 0.94 (9H, s), 0.17 (3H, s),
0.13 (3H, s); 13C NMR (100 MHz, CDCl3) d 207.7, 137.1,
135.1, 134.8, 130.4, 128.5, 128.5, 128.5, 126.4, 126.4,
126.1, 126.1, 125.5, 101.4, 88.9, 26.9, 26.9, 21.0, 21.0,
18.4, ꢁ4.5, ꢁ4.9; HRMS (ESI) m/z calcd for C22H28NaSi
343.1858 (M++Na), found 343.1858.
4.3.12. 3-tert-Butyldimethylsilyl-1-(2-methylphenyl)-1-
phenyl-2-propyne (10). Yield 34%; 20% ee; colorless oil;
[a]2D8 ꢁ7.3 (c 0.7, CHCl3); enantiomeric excess was deter-
mined by HPLC analysis [CHIRALPAC IA column, 100%
hexane, 0.2 mL/min, l¼254 nm, retention times 22.1 min
(minor) and 23.2 min (major)]; IR (neat) 2952, 2928, 2170,
1601, 1493 cmꢁ1; 1H NMR (400 MHz, CDCl3) d 7.44 (1H,
d, J¼8.0 Hz), 7.42–7.12 (8H, m), 5.19 (1H, s), 2.28 (3H, s),
0.93 (9H, s), 0.11 (6H, s); 13C NMR (100 MHz, CDCl3)
d 140.6, 139.3, 135.9, 130.6, 128.8, 128.4, 128.4, 127.9,
127.9, 127.0, 126.6, 126.2, 107.2, 87.0, 41.3, 26.1, 26.1,
26.1, 19.6, 16.7, ꢁ4.5, ꢁ4.5; HRMS (ESI) m/z calcd for
C22H29Si 321.2042 (M++H), found 321.2041.
5. (a) Yoshida, M.; Ueda, H.; Ihara, M. Tetrahedron Lett. 2005, 46,
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Tetrahedron Lett. 2004, 45, 5573; (d) Moriya, T.; Miyaura, N.;
Suzuki, A. Synlett 1994, 149.
6. The absolute configuration of the resulting allene 3a was deter-
mined as R on the basis of Lowe’s rule: Lowe, G. J. Chem. Soc.,
Chem. Commun. 1965, 411.
7. Molander et al. examined the effect of base in the enantiospecific
coupling of propargylic carbonates with alkenylboron com-
pounds, see Ref. 5b.
Acknowledgements
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This study was supported in part by a Grant-in-Aid for the
Encouragement of Young Scientists (B) from the Japan So-
ciety for the Promotion of Science (JSPS), Takeda Science