Synthesis of allenylsilanes through copper-catalyzed γ-selective coupling between γ-silylated propargylic phosphates and alkylboranes

Article abstract of DOI:10.1021/om300552f

Copper-catalyzed γ-selective coupling between γ-silylated propargylic phosphates and alkylboron compounds (alkyl-9-BBN, prepared by hydroboration of alkenes with 9-BBN-H) produced allenylsilanes with exceptional selectivity. The reaction tolerated various

Full text of DOI:10.1021/om300552f

Article
pubs.acs.org/Organometallics
Synthesis of Allenylsilanes through Copper-Catalyzed γ-Selective
Coupling between γ-Silylated Propargylic Phosphates and
Alkylboranes
Umi Yokobori, Hirohisa Ohmiya,* and Masaya Sawamura*
Department of Chemistry, Faculty of Science, Hokkaido University, Sapporo 060-0810, Japan
S
* Supporting Information
ABSTRACT: Copper-catalyzed γ-selective coupling between γ-
silylated propargylic phosphates and alkylboron compounds (alkyl-
9-BBN, prepared by hydroboration of alkenes with 9-BBN-H)
produced allenylsilanes with exceptional selectivity. The reaction
tolerated various functional groups in both the alkylboranes and the
propargylic phosphates to afford functionalized allenylsilanes. The
reaction of enantioenriched γ-silylated propargylic phosphates
proceeded with excellent 1,3-anti stereoselectivity to give axially
chiral allenylsilanes.
llenylsilanes are useful reagents in organic synthesis
because of their applicability toward various trans-
Scheme 1
A
formations.1 For example, the addition to carbonyl compounds
offers a general approach to homopropargylic alcohols.2 Thus,
the development of facile and efficient methods for the
synthesis of allenylsilanes is important. In particular, methods
for accessing enantioenriched allenylsilanes are highly desirable.
Among the available methods for the preparation of
allenylsilanes, two types of SN2′ displacement strategies, γ
substitutions of γ-silylated propargylic alcohol derivatives with
organocuprate reagents3 and silylations of propargylic alcohol
derivatives,4−7 are the most straightforward because the
substrates and the reagents are readily available and the
reactions are highly reliable in terms of product yield and
selectivity.
Earlier, we developed copper-catalyzed γ-selective coupling
between propargylic phosphates and alkylboron compounds
(alkyl-9-BBN, prepared by hydroboration of alkenes with 9-
BBN-H).8a Herein, we report the expansion of this protocol to
the reaction between γ-silylated propargylic phosphates and
alkylboranes, which affords a straightforward, functional-group-
tolerable approach to allenylsilanes.8−10 The protocol is
applicable to the stereocontrolled transformation of enantioen-
riched secondary propargylic phosphates to axially chiral
allenylsilanes, which occurred with excellent 1,3-anti stereo-
selectivity.
a diethyl phosphate as a leaving group resulted in a significantly
decreased product yield.
The hydroboration−coupling one-pot protocol was appli-
cable to the synthesis of the allenylsilanes with different
substitution patterns (Table 1). The reaction of α-unsub-
stituted primary propargylic phosphate 3b proceeded in high
yield with the complete γ selectivity unchanged (94%) (entry
1). The α-PhCH2CH2 substituent in the secondary propargylic
phosphate 3a could be replaced with MOMO(CH2)4 (3c)
groups without a drastic change in the yield of allene 4ac (entry
2). The sterically more demanding i-Pr group was also tolerated
as an α substituent, and the corresponding allene 4ad was
obtained in 90% yield (entry 3). Tertiary propargylic phosphate
3e was much less reactive, giving the corresponding
tetrasubstituted allene in only a low yield (entry 4). Propargylic
phosphates 3f−i with silyl substituents such as Me3Si, Et3Si,
Alkylborane 2a (0.3 mmol), which was prepared via
hydroboration of styrene (1a) with 9-borabicyclo[3.3.1]nonane
(9-BBN-H) dimer, and γ-tert-butyldimethylsilyl-substituted
propargylic substrate 3a (0.2 mmol,) bearing a diphenyl
phosphate leaving group, were subjected to the reaction
conditions for the copper-catalyzed coupling (2a/3a/CuOAc/
t-BuOK 1.5/1/0.1/1.0, THF, 60 °C) (Scheme 1).8a The
reaction afforded allenylsilane 4aa in 79% yield (based on 3a;
100% conversion of 3a) with complete γ selectivity. The use of
t
and PhMe2Si instead of BuMe2Si at the γ position were also
Special Issue: Copper Organometallic Chemistry
Received: June 18, 2012
Published: July 11, 2012
© 2012 American Chemical Society
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Article
a
(1g), also proceeded, albeit in a moderate yield, and gave 4ga as
a 1/1 diastereomeric mixture (entry 14). The use of secondary
alkylborane reagents prepared from internal alkenes resulted in
no reaction (data not shown).
Table 1. Synthesis of Allenylsilanes
A variety of functionalized allenylsilanes can be synthesized
through the copper-catalyzed reaction of silicon-substituted
propargylic phosphates (Table 1). Specifically, the MOM ether
in the propargylic phosphate 3c and ester, acetal, and silyloxy
moieties at the terminus of the aliphatic chain of alkene
substrates were compatible with the protocol (entries 2 and 9−
11). Methoxy and silyloxy moieties on the aromatic ring were
also tolerated (entries 12 and 13).
The present Cu-catalyzed protocol is effective for the
stereocontrolled synthesis of axially chiral, nonracemic
allenylsilanes (Scheme 2). The reaction between the styrene-
Scheme 2. Synthesis of Axially Chiral, Nonracemic
Allenylsilanes
derived alkylborane 2a and the enantioenriched propargylic
phosphate (R)-3i (99% ee), which has α-Me and γ-PhMe2Si
substituents, proceeded with excellent stereoselectivity to afford
the enantioenriched allenylsilane 4ai (95% ee). The subsequent
TiCl4-mediated addition of 4ai to isobutyraldehyde afforded
the homopropargylic alcohol (3S,4S)-5 (95% ee).7c The
diastereomer ratio (syn/anti, dr) with respect to the
consecutive chiral centers was >20/1. The excellent syn
selectivity suggests that the addition of the allenylsilane 4ai
to the aldehyde proceeded through an acyclic antiperiplanar
transition state.1e,2 On the basis of the established 1,3-anti
stereochemical pathway on the Lewis acid mediated addition of
allenylsilanes to aldehydes,1e the absolute configuration of the
axially chiral allenylsilane 4ai was deduced to be R. Therefore, it
is concluded that the copper-catalyzed coupling of (R)-3i
proceeded with 1,3-anti stereochemistry. The reactions with the
bulkier alkylborane 2b or the allylbenzene-derived alkylborane
2f also occurred with excellent stereoselectivity to give the
corresponding chiral allenylsilanes (−)-4bi (94% ee) or (−)-4fi
(93% ee).
The 1,3-anti stereochemical outcome in the present copper
catalysis with γ-silicon-substituted propagylic phosphates is in
common with that with non-silicon-substituted propagylic
phosphates.8a Accordingly, it is conceivable that the present
copper catalysis also proceeds through the addition−anti-
elimination mechanism of a neutral alkylocopper species (B), as
shown in Scheme 3. During this addition−elimination pathway
(C → D → (R)-4) tert-butoxyborane, which is derived from the
transmetalation between CuX (X  OP(O)(OPh)2, OAc) and
the trialkyl(alkoxo)borate A, may play a role in activating the
phosphate leaving group through its Lewis acidic charac-
ter.10c,11 The 1,3-anti stereochemistry should be determined at
the elimination step.
a
The reaction was carried out with 3 (0.4 mmol), alkylborane 2 (0.6
mmol), CuOAc (10 mol %), and t-BuOK (1.0 equiv, 1 M in THF) in
THF (0.86 mL) at 60 °C for 4 h. Alkylborane 2 was prepared in
advance by hydroboration of 1 with 9-BBN-H dimer in THF at 60 °C
b
for 1 h and was used without purification. Yield of the isolated
product based on 3. γ/α > 99:1. Determined by H NMR or GC
c
1
d
analysis of the crude product. THF (3.5 mL) was used.
e
Diastereomeric ratio (1:1).
reactive, affording the corresponding allenylsilane derivatives
4af,ag,ah,ai in high yields (entries 5−8).
The tolerance of the reaction toward steric demand in
alkylboranes (2) was evaluated in Table 1, entries 9 and 14.
The sterically more demanding alkylborane 2b, which was
derived from a tertiary-alkyl-substituted terminal alkene (1b),
served as a substrate to afford the corresponding allene 4ba in
good yield (entry 9). The reaction of the β-branched
alkylborane (2g), which was prepared from α-methylstyrene
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containing the Cu salt. Finally, propargylic phosphate 3a (106 mg, 0.2
mmol) was added. After 12 h of stirring at 60 °C, CH2Cl2 was added
to the mixture. Then, the mixture was filtered through Celite and silica
gel, which was washed with diethyl ether. After the solvent was
removed under reduced pressure, flash chromatography on silica gel
(hexane) provided 4aa (57.2 mg, 0.158 mmol) in 79% yield.
Characterization Data for Allenylsilanes. 3-(tert-Butyldime-
thylsilyl)-1,7-diphenyl-3,4-heptadiene (4aa). Oil. 1H NMR (300
MHz, CDCl3): δ 0.03 (s, 6H), 0.89 (s, 9H), 2.20 (td, J = 8.1, 3.3 Hz,
2H), 2.25−2.33 (m, 2H), 2.57−2.75 (m, 4H), 4.89 (m, 1H), 7.15−
7.21 (m, 6H), 7.26−7.31 (m, 4H). 13C NMR (75.4 MHz, CDCl3): δ
−6.25, −6.08, 17.77, 26.65, 30.66, 31.88, 35.29, 36.20, 85.97, 94.43,
125.74, 125.90, 128.30, 128.36, 128.55, 128.58, 142.15, 142.79, 206.80.
HRMS-FD (m/z): [M]+ calcd for C25H34Si, 362.242 98; found,
362.243 08.
Scheme 3. Possible Pathway
3-(tert-Butyldimethylsilyl)-5-phenyl-1,2-pentadiene (4ab). Oil. 1H
NMR (300 MHz, CDCl3): δ 0.05 (s, 6H), 0.89 (s, 9H), 2.22 (tt, J =
8.1, 3.6 Hz, 2H), 2.77 (t, J = 8.1 Hz, 2H), 4.41 (t, J = 3.6 Hz, 2H),
7.16−7.21 (m, 3H), 7.26−7.31 (m, 2H). 13C NMR (75.4 MHz,
CDCl3): δ −6.40, 18.18, 26.60, 31.29, 35.23, 69.96, 92.35, 125.82,
128.35, 128.58, 142.67, 209.73. HRMS-APCI (m/z): [M + H]+ calcd
for C17H27Si, 259.187 65; found, 259.187 49.
In conclusion, we have developed a versatile, functional-
group-tolerant approach to allenylsilanes through a copper-
catalyzed γ-selective coupling reaction between γ-silylated
propargylic phosphates and alkylboranes. The excellent 1,3-
anti stereoselectivity allows the efficient preparation of axially
chiral, nonracemic allenylsilanes from enantioenriched, γ-
silylated propargylic alcohols. The availability of alkylboranes
through in situ alkene hydroboration and broad functional
group compatibility in both the propargylic and alkylboron
substrates are attractive features from a synthetic viewpoint.
3-(tert-Butyldimethylsilyl)-9-(methoxymethoxymethyl)-1-phenyl-
1
3,4-nonadiene (4ac). Oil. H NMR (300 MHz, CDCl3): δ 0.03 (s,
6H), 0.89 (s, 9H), 1.41−1.51 (m, 2H), 1.57−1.69 (m, 2H), 2.00 (q, J
= 7.2 Hz, 2H), 2.19−2.26 (m, 2H), 2.71−2.77 (m, 2H), 3.56 (s, 3H),
3.53 (t, J = 6.6 Hz, 2H), 4.62 (s, 2H), 4.84 (m, 1H), 7.15−7.21 (m,
3H), 7.25−7.31 (m, 2H). 13C NMR (75.4 MHz, CDCl3): δ −6.25,
−6.08, 17.75, 26.47, 26.65, 28.49, 29.28, 31.97, 35.41, 55.02, 67.62,
86.34, 94.07, 96.40, 125.74, 128.30, 128.53, 142.78, 206.93. HRMS-
ESI (m/z): [M + Na]+ calcd for C23H38O2SiNa 397.253 33; found,
397.252 92.
3-(tert-Butyldimethylsilyl)-6-methyl-1-phenyl-3,4-heptadiene
(4ad). Oil. 1H NMR (300 MHz, CDCl3): δ 0.04 (s, 6H), 0.90 (s, 9H),
1.00 (d, J = 6.6 Hz, 3H), 1.01 (d, J = 6.9 Hz, 3H), 2.20−2.31 (m, 3H),
2.70−2.77 (m, 2H), 4.87 (m, 1H), 7.18−7.21 (m, 3H), 7.25−7.31 (m,
2H). 13C NMR (75.4 MHz, CDCl3): δ −6.28, −5.86, 17.90, 22.89,
23.06, 26.77, 27.85, 32.11, 35.45, 94.37, 95.46, 125.75, 128.34, 128.53,
142.92, 205.46. HRMS-APCI (m/z): [M + H]+ calcd for C20H33Si,
301.234 60; found, 301.234 32.
EXPERIMENTAL SECTION
■
All reactions were carried out under a nitrogen or argon atmosphere.
Materials were obtained from commercial suppliers or prepared
according to standard procedures unless otherwise noted. t-BuOK (1.0
M THF solution) and CuOAc were purchased from Aldrich Chemical
Co., stored under nitrogen, and used as is. THF was purchased from
Kanto Chemical Co. and stored under argon. NMR spectra were
recorded on a Varian Gemini 2000 spectrometer, operating at 300
MHz for 1H NMR and 75.4 MHz for 13C NMR. Chemical shift values
for 1H and 13C are referenced to Me4Si and the residual solvent
resonances, respectively. Chemical shifts are reported in δ (ppm).
Mass spectra were obtained with Thermo Fisher Scientific Exactive,
JEOL JMS-T100 GC, and JEOL JMS-T100LP instruments at the
Center for Instrumental Analysis, Hokkaido University. TLC analyses
were performed on commercial glass plates bearing 0.25 mm layers of
Merck silica gel 60F254. Silica gel (Kanto Chemical Co., silica gel 60 N,
spherical, neutral) and aluminum oxide (Nacalai Tesuque, alumina
activated 200) were used for column chromatography. HPLC analyses
were conducted on a Hitachi ELITE LaChrom system with a Hitachi
L-2400 UV detector or a Shimadzu LC-6A system with a Shimadzu
SPD-10A UV detector. Gel permeation chromatography (GPC) was
performed with an LC-908 instrument (Japan Analytical Industry Ltd.,
two in-line JAIGEL-2H columns, CHCl3, 3.5 mL/min, UV and RI
detectors).
4-(tert-Butyldimethylsilyl)-1-methyl-6-phenyl-2,3-hexadiene
(4ae). Oil. 1H NMR (300 MHz, CDCl3): δ 0.00 (s, 6H), 0.88 (s, 9H),
1.62 (s, 3H), 1.63 (s, 3H), 2.21 (t, J = 8.1 Hz, 2H), 2.71 (t, J = 8.1 Hz,
2H), 7.14−7.21 (m, 3H), 7.25−7.30 (m, 2H). 13C NMR (75.4 MHz,
CDCl3): δ −6.09, 17.21, 19.99 (×2C), 26.58, 32.23, 35.52, 90.02,
92.21, 125.61, 128.24, 128.54, 143.00, 206.17. HRMS-EI (m/z): [M]+
calcd for C19H30Si, 286.211 68; found, 286.212 05.
1
1,7-Diphenyl-3-trimethylsilyl-3,4-heptadiene (4af). Oil. H NMR
(300 MHz, CDCl3): δ 0.07 (s, 9H), 2.20 (td, J = 8.1, 3.0 Hz, 2H),
2.25−2.31 (m, 2H), 2.58−2.75 (m, 4H), 4.90 (m, 1H), 7.15−7.20 (m,
6H), 7.26−7.31 (m, 4H). 13C NMR (75.4 MHz, CDCl3): δ −1.68,
30.22, 31.00, 35.32, 36.00, 85.86, 96.75, 125.77, 125.86, 128.31,
128.35, 128.54, 128.57, 142.17, 142.70, 205.54. HRMS-FD (m/z):
[M]+ calcd for C22H28Si, 320.196 03; found, 320.196 62.
1,7-Diphenyl-3-triethylsilyl-3,4-heptadiene (4ag). Oil. 1H NMR
(300 MHz, CDCl3): δ 0.58 (q, J = 7.8 Hz, 6H), 0.93 (t, J = 7.8 Hz,
9H), 2.17 (td, J = 8.1, 3.0 Hz, 2H), 2.28 (q, J = 7.5 Hz, 2H), 2.58−2.76
(m, 4H), 4.86 (m, 1H), 7.15−7.20 (m, 6H), 7.26−7.30 (m, 4H). 13C
NMR (75.4 MHz, CDCl3): δ 2.98, 7.27, 30.62, 31.28, 35.19, 36.11,
85.53, 93.52, 125.74, 125.87, 128.29, 128.35, 128.53, 128.58, 142.19,
142.77, 206.29. HRMS-ESI (m/z): [M + Na]+ calcd for C25H34SiNa,
385.232 20; found, 385.232 09.
Typical Procedure for Synthesis of Allenylsilanes (Scheme
1). In a glovebox, (9-BBN-H)2 (36.6 mg, 0.15 mmol), THF (0.43
mL), and styrene (1a; 40 μL, 0.36 mmol) were sequentially placed in a
vial containing a magnetic stirring bar. On the other hand, in the
glovebox, CuOAc (2.5 mg, 0.02 mmol) was placed in another vial
containing a magnetic stirring bar. Then, the two vials were sealed with
a cap equipped with a Teflon-coated silicon rubber septum. The vials
were removed from the glovebox. After the mixture in THF was stirred
at 60 °C for 1 h to prepare alkylborane 2a, t-BuOK (1 M in THF, 0.2
mL, 0.2 mmol) was added to 2a prepared in advance at 25 °C, and the
mixture was stirred at 25 °C for 5 min to produce the corresponding
alkylborate. Next, the alkylborate was then transferred to the other vial
1
6-Phenyl-4-triethylsilyl-2,3-hexadiene (4ah). Oil. H NMR (300
MHz, CDCl3): δ 0.59 (q, J = 7.8 Hz, 6H), 0.93 (d, J = 7.8 Hz, 9H),
1.59 (d, J = 6.9 Hz, 3H), 2.19 (td, J = 8.1, 3.3 Hz, 2H), 2.73 (td, J =
8.1, 2.7 Hz, 2H), 4.79 (m, 1H), 7.15−7.21 (m, 3H), 7.25−7.30 (m,
2H). 13C NMR (75.4 MHz, CDCl3): δ 3.00, 7.22, 13.89, 31.31, 35.30,
80.36, 92.40, 125.71, 128.29, 128.55, 142.81, 207.46. HRMS-EI (m/z):
[M]+ calcd for C18H28Si, 272.196 03; found, 272.195 39.
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Methyl 6-(tert-Butyldimethylsilyl)-3,3-dimethyl-10-phenyl-6,7-
13.67, 31.13, 35.26, 81.27, 94.29, 125.68, 127.80, 128.23, 128.55,
1
129.07, 133.92, 138.44, 142.54, 207.86. HRMS-EI (m/z): [M]+ calcd
decadienoate (4ba). Oil. H NMR (300 MHz, CDCl3): δ 0.04 (s,
24
6H), 0.90 (s, 9H), 0.99 (s, 6H), 1.36−1.43 (m, 2H), 1.86−1.92 (m,
2H), 2.20 (s, 2H), 2.24−2.31 (m, 2H), 2.70 (t, J = 7.8 Hz, 2H), 3.64
(s, 3H), 4.84 (m, 1H), 7.15−7.21 (m, 3H), 7.26−7.31 (m, 2H). 13C
NMR (75.4 MHz, CDCl3): δ −6.20, −6.02, 17.73, 24.33, 26.66, 27.06,
30.62, 33.05, 36.23, 41.71, 45.87, 51.05, 82.62, 94.67, 125.87, 128.37,
128.54, 142.21, 172.93, 206.79. HRMS-ESI (m/z): [M + Na]+ calcd
for C25H40O2SiNa, 423.268 98; found, 423.268 59.
10-(tert-Butyldimethylsilyl)-1-(1,3-dioxane)-14-phenyl-10,11-tet-
radecadiene (4ca). Oil. 1H NMR (300 MHz, CDCl3): δ 0.03 (s, 6H),
0.89 (s, 9H), 1.26−1.39 (m, 15H), 1.55−1.62 (m, 2H), 1.86−1.92 (m,
2H), 1.99−2.16 (m, 1H), 2.24−2.31 (m, 2H), 2.69 (t, J = 7.8 Hz, 2H),
3.75 (td, J = 12.3, 2.4 Hz, 2H), 4.10 (dd, J = 10.5, 5.1 Hz, 2H), 4.50 (t,
J = 5.1 Hz, 1H), 4.81 (m, 1H), 7.15−7.20 (m, 3H), 7.25−7.30 (m,
2H). 13C NMR (75.4 MHz, CDCl3): δ −6.19, −6.03, 17.73, 23.87,
25.75, 26.68, 28.94, 29.33, 29.40, 29.43, 29.48 (×2C), 29.91, 30.72,
35.17, 36.28, 66.84, 85.17, 94.63, 102.48, 125.80, 128.32, 128.53,
142.25, 206.69. HRMS-ESI (m/z): [M + Na]+ calcd for
C30H50O2SiNa, 493.347 23; found, 493.346 70.
for C20H24Si, 292.164 73; found, 292.163 60. [α]D = −3.54° (c 1.00,
CHCl3). The ee value (95%) was determined by chiral HPLC analysis
of 4ai: CHIRALCEL OD-3 column (Daicel Chemical Industries), 4.6
mm × 250 mm, hexane, 0.5 mL/min, 40 °C, 220 nm UV detector,
retention time 11.8 min for the R isomer and 14.2 min for the S
isomer.
(−)-Methyl 3,3-Dimethyl-5-dimethylphenylsilyl-6,7-nonadie-
1
noate ((−)-4bi). Oil. H NMR (300 MHz, CDCl3): δ 0.35 (s, 6H),
0.92 (s, 6H), 1.35−1.41 (m, 2H), 1.62 (d, J = 6.9 Hz, 3H), 1.84−1.90
(m, 2H), 2.13 (s, 2H), 3.61 (s, 3H), 4.83 (m, 1H), 7.34−7.36 (m, 3H),
7.51−7.53 (m, 2H). 13C NMR (75.4 MHz, CDCl3): δ −3.04, −2.95,
13.72, 23.93, 26.94, 33.08, 41.77, 45.82, 51.00, 80.89, 94.63, 127.77,
129.03, 133.91, 138.59, 172.92, 207.83. HRMS-ESI (m/z): [M + Na]+
24
calcd for C20H30O2SiNa, 353.190 73; found, 353.190 56. [α]D
=
−4.34° (c 1.05, CHCl3). The ee value (94%) was determined by chiral
HPLC analysis of 4bi: CHIRALCEL OD-3 column (Daicel Chemical
Industries), 4.6 mm × 250 mm, hexane, 0.5 mL/min, 40 °C, 220 nm
UV detector, retention time 14.6 min for the minor isomer and 15.7
min for the major isomer.
10-(tert-Butyldimethylsiloxy)-5-(tert-butyldimethylsilyl)-1-phenyl-
1
3,4-decadiene (4da). Oil. H NMR (300 MHz, CDCl3): δ 0.03 (s,
(−)-7-(4-tert-Butyldimethylsiloxy-3-methoxyphenyl)-4-dimethyl-
phenylsilyl-2,3-heptadiene ((−)-4fi). Oil. 1H NMR (300 MHz,
CDCl3): δ 0.13 (s, 6H), 0.34 (s, 6H), 0.99 (s, 9H), 1.63−1.72 (m,
5H), 1.93 (td, J = 7.2, 2.7 Hz, 2H), 2.49 (t, J = 7.8 Hz, 2H), 3.75 (s,
3H), 4.84 (m, 1H), 6.54 (dd, J = 8.1, 0.4 Hz, 1H), 6.59 (d, J = 0.4 Hz,
1H), 6.71 (d, J = 8.1 Hz, 1H), 7.26−7.36 (m, 3H), 7.51−7.54 (m,
2H). 13C NMR (75.4 MHz, CDCl3): δ −4.80, −3.13, −3.03, 13.79,
18.31, 25.64, 28.80, 30.83, 34.94, 55.39, 80.65, 94.23, 112.57, 120.53,
120.57, 127.77, 129.02, 133.90, 136.27, 138.66, 142.90, 150.64, 207.81.
HRMS−ESI (m/z): [M + Na]+ calcd for C28H42O2Si2Na, 489.261 55;
6H), 0.04 (s, 6H), 0.89 (s, 18H), 1.28−1.43 (m, 4H), 1.49−1.56 (m,
2H), 1.87−1.93 (m, 2H), 2.24−2.31 (m, 2H), 2.69 (t, J = 7.8 Hz, 2H),
3.60 (t, J = 6.6 Hz, 2H), 4.82 (m, 1H), 7.15−7.20 (m, 3H), 7.25−7.30
(m, 2H). 13C NMR (75.4 MHz, CDCl3): δ −6.20, −6.03, −5.42,
17.73, 18.27, 25.52, 25.89, 26.68, 28.72, 29.87, 30.73, 32.75, 36.29,
63.31, 85.25, 94.56, 125.83, 128.34, 128.55, 142.23, 206.68. HRMS-
ESI (m/z): [M + Na]+ calcd for C28H50OSi2Na, 481.329 24; found,
481.328 88.
5-(tert-Butyldimethylsilyl)-8-(3,4-dimethoxyphenyl)-1-phenyl-3,4-
1
nonadiene (4ea). Oil. H NMR (300 MHz, CDCl3): δ 0.03 (s, 6H),
0.89 (s, 9H), 1.66−1.76 (m, 2H), 1.96 (td, J = 7.5, 3.0 Hz, 2H), 2.26−
2.33 (m, 2H), 2.57 (t, J = 7.8 Hz, 2H), 2.70 (t, J = 7.8 Hz, 2H), 3.85
(s, 6H), 4.86 (m, 1H), 6.70−6.72 (m, 2H), 6.77−6.80 (m, 1H), 7.16−
7.19 (m, 3H), 7.24−7.28 (m, 2H). 13C NMR (75.4 MHz, CDCl3): δ
−6.19, −6.01, 17.73, 26.67, 29.39, 30.76, 30.80, 35.07, 36.27, 55.70,
55.87, 85.48, 94.34, 111.21, 111.82, 120.24, 125.86, 128.35, 128.52,
135.47, 142.13, 147.13, 148.83, 206.67. HRMS-ESI (m/z): [M + Na]+
calcd for C28H40O2SiNa 459.268 98; found, 459.268 47.
24
found, 489.261 27. [α]D = −3.46° (c 1.01, CHCl3). The ee value
(93%) was determined by chiral HPLC analysis of 4fi: CHIRALCEL
OD-3 column (Daicel Chemical Industries), 4.6 mm × 250 mm,
hexane/2-propanol 99.5/0.5, 0.5 mL/min, 40 °C, 220 nm UV
detector, retention time 10.7 min for the major isomer and 11.6
min for the minor isomer.
(3S,4S)-2,4-Dimethyl-8-phenyl-5-octyn-3-ol ((3S,4S)-5). Alle-
nylsilane 4ai (29.2 mg, 0.1 mmol) was added to a screw-vial tube
equipped with a magnetic stirring bar. The tube was sealed with a cap
equipped with a Teflon-coated silicon rubber septum. The air inside
was removed in vacuo through a needle and substituted with Ar. After
the addition of i-PrCHO (14 μL, 0.15 mmol) and CH2Cl2 (0.7 mL), a
solution of TiCl4 in CH2Cl2 (0.5 M, 0.3 mL, 0.15 mmol) was added
dropwise at −78 °C, and the mixture was stirred for 2 h at this
temperature. Then Et2O and 2 N aqueous HCl were added. After it
was stirred at room temperature for 10 min, the mixture was
neutralized with saturated NaHCO3 and the organic layer was
separated. The aqueous layer was extracted with Et2O (two times).
The organic layers were combined, passed through a pad of silica gel,
and concentrated to dryness; purification by flash chromatography on
silica gel afforded (3S,4S)-5 in 61% yield (14 mg, 0.061 mmol) as a
8-(4-tert-Butyldimethylsiloxy-3-methoxyphenyl)-5-(tert-butyldi-
1
methylsilyl)-1-phenyl-3,4-octadiene (4fa). Oil. H NMR (300 MHz,
CDCl3): δ 0.01 (s, 6H), 0.14 (s, 6H), 0.88 (s, 9H), 0.99 (s, 9H), 1.64−
1.74 (m, 2H), 1.90−1.96 (m, 2H), 2.26−2.33 (m, 2H), 2.54 (t, J = 7.8
Hz, 2H), 2.70 (t, J = 7.8 Hz, 2H), 3.77 (s, 3H), 4.85 (m, 1H), 6.59−
6.66 (m, 2H), 6.75 (d, J = 8.1 Hz, 1H), 7.14−7.19 (m, 3H), 7.24−7.29
(m, 2H). 13C NMR (75.4 MHz, CDCl3): δ −6.20, −6.03, −4.81,
17.73, 18.33, 25.66, 26.68, 29.30, 30.68, 30.79, 35.12, 36.29, 55.40,
85.43, 94.36, 112.58, 120.57, 120.64, 125.86, 128.36, 128.55, 136.26,
142.16, 142.96, 150.70, 206.68. HRMS-ESI (m/z): [M + Na]+ calcd
for C33H52O2Si2Na, 559.339 81; found, 559.339 35.
3-(tert-Butyldimethylsilyl)-1,7-diphenyl-1-methyl-3,4-heptadiene
(4ga). Oil. 1H NMR (300 MHz, CDCl3): δ 0.02 (s, 0.5 × 6H), 0.03 (s,
0.5 × 3H), 0.04 (s, 0.5 × 3H), 0.89 (s, 0.5 × 9H), 0.89 (s, 0.5 × 9H),
1.24 (d, J = 6.9 Hz, 0.5 × 3H, 0.5 × 3H), 2.07−2.19 (m, 0.5 × 2H, 0.5
× 2H), 2.24−2.36 (m, 0.5 × 2H, 0.5 × 2H), 2.59 (td, J = 7.8, 4.3 Hz,
0.5 × 2H), 2.70 (t, J = 7.8 Hz, 0.5 × 2H), 2.86−2.95 (m, 0.5 × 1H, 0.5
× 1H), 4.76−4.81 (m, 0.5 × 1H, 0.5 × 1H), 7.16−7.22 (m, 0.5 × 3H,
0.5 × 3H), 7.27−7.33 (m, 0.5 × 2H, 0.5 × 2H). 13C NMR (75.4 MHz,
CDCl3): δ −6.21, −6.16, −6.06, −5.99, 17.78, 17.83, 21.48, 22.07,
26.67, 26.69, 30.52, 30.64, 36.08, 36.37, 38.39, 38.75, 38.92, 39.04,
85.40, 85.46, 92.87, 92.93, 125.81, 125.83 (×2C), 125.89, 127.18,
127.25 (×4C), 128.33, 128.37, 128.57, 128.58, 142.16, 142.23, 147.92,
147.99, 207.22, 207.29. HRMS-ESI (m/z): [M + Na]+ calcd for
C26H36SiNa, 399.247 85; found, 399.247 91.
1
pale yellow oil. H NMR (300 MHz, CDCl3): δ 0.88 (d, J = 6.9 Hz,
3H), 0.92 (d, J = 6.9 Hz, 3H), 1.13 (d, J = 6.9 Hz, 3H), 1.59 (s, 1H),
1.85 (m, 1H), 2.47 (td, J = 7.5, 2.1 Hz, 2H), 2.55 (m, 1H), 2.80 (t, J =
7.5 Hz, 2H), 3.21 (t, J = 5.7 Hz, 1H), 7.13−7.23 (m, 3H), 7.26−7.32
(m, 2H). 13C NMR (75.4 MHz, CDCl3): δ 15.31, 16.99, 19.39, 20.79,
29.95, 30.17, 35.26, 79.17, 81.41, 83.34, 126.32, 128.40, 128.56,
140.88. HRMS-ESI (m/z): [M + Na]+ calcd for C16H22ONa 253.156
29; found, 253.156 22. [α]D24 = −1.58° (c 0.80, CHCl3). The ee value
(95%) was determined by chiral HPLC analysis of a p-nitrobenzoate
derivative of 5: CHIRALCEL OD-3 column (Daicel Chemical
Industries), 4.6 mm × 250 mm, hexane/2-propanol 99.5/0.5, 0.5
mL/min, 40 °C, 250 nm UV detector, retention time 43.0 min for the
3S,4S isomer and 45.7 min for the 3R,4R isomer. The absolute
configuration of (3S,4S)-5 was determined by Mosher’s NMR
spectroscopic method.
(R)-(−)-4-(tert-Butyldimethylsilyl)-6-phenyl-2,3-hexadiene ((R)-
1
(−)-4ai). Oil. H NMR (300 MHz, CDCl3): δ 0.35 (s, 6H), 1.60 (d,
J = 6.9 Hz, 3H), 2.16−2.22 (m, 2H), 2.66−2.71 (m, 2H), 4.87 (m,
1H), 7.09−7.17 (m, 3H), 7.21−7.26 (m, 2H), 7.32−7.36 (m, 3H),
7.50−7.53 (m, 2H). 13C NMR (75.4 MHz, CDCl3): δ −3.21, −3.09,
7912
dx.doi.org/10.1021/om300552f | Organometallics 2012, 31, 7909−7913

Organometallics
Article
(10) For Cu-catalyzed γ-selective allylic substitutions with alkyl-9-
BBN, see: (a) Ohmiya, H.; Yokobori, U.; Makida, Y.; Sawamura, M. J.
Am. Chem. Soc. 2010, 132, 2895−2897. (b) Nagao, K.; Ohmiya, H.;
Sawamura, M. Synthesis 2012, 44, 1535−1541. (c) Nagao, K.;
Yokobori, U.; Makida, Y.; Ohmiya, H.; Sawamura, M. J. Am. Chem.
Soc. 2012, 134, 8982−8987.
ASSOCIATED CONTENT
■
S
* Supporting Information
Text and figures giving experimental details and character-
ization data for new compounds. This material is available free
of charge via the Internet at http://pubs.acs.org.
(11) We confirmed the formation of borate A from 2a and t-BuOK in
THF by 11B NMR spectroscopy.10a This is in sharp contrast to the
resistance of a similar alkylborane reagent upon treatment with t-
BuOLi in both toluene and 1,4-dioxane.9
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: ohmiya@sci.hokudai.ac.jp (H.O.); sawamura@sci.
hokudai.ac.jp (M.S.).
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by CREST, JST, to M.S. and by
Grants-in-Aid for Young Scientists (A), JSPS, and by the
Uehara Memorial Foundation to H.O.
REFERENCES
■
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(8) For Cu-catalyzed γ-selective coupling between alkyl-9-BBN and
propargylic phosphates, see: (a) Ohmiya, H.; Yokobori, U.; Makida,
Y.; Sawamura, M. Org. Lett. 2011, 13, 6312−6315. For Cu-catalyzed γ-
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dx.doi.org/10.1021/om300552f | Organometallics 2012, 31, 7909−7913