Stereoselective preparation of (E)- and (Z)-di- and trisubstituted 1,3-butadienes

Article abstract of DOI:10.1016/j.tetlet.2015.04.114

Abstract The reaction of γ-(trimethylsilyl)allyltitanocenes, generated by the desulfurizative titanation of trimethylsilyl-substituted allylic sulfides with the titanocene(II)-1-butene complex, with ketones produced β-hydroxy silanes with good to complete

Full text of DOI:10.1016/j.tetlet.2015.04.114

Tetrahedron Letters 56 (2015) 4016–4021
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Tetrahedron Letters
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Stereoselective preparation of (E)- and (Z)-di- and trisubstituted
1,3-butadienes
⇑
Takeshi Takeda , Keiichiro Tateishi, Akira Tsubouchi
Department of Applied Chemistry, Graduate School of Engineering, Tokyo University of Agriculture and Technology, Koganei, Tokyo 184-8588, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of
c-(trimethylsilyl)allyltitanocenes, generated by the desulfurizative titanation of
Received 17 March 2015
Revised 23 April 2015
Accepted 28 April 2015
Available online 9 May 2015
trimethylsilyl-substituted allylic sulfides with the titanocene(II)–1-butene complex, with ketones pro-
duced b-hydroxy silanes with good to complete anti-selectivity. Both (E)- and (Z)-1,1-disubstituted as
well as 1,1,2-trisubstituted 1,3-butadienes are obtained stereoselectively by their Peterson elimination
under acidic or basic conditions.
Ó 2015 Elsevier Ltd. All rights reserved.
Keywords:
Conjugated dienes
Stereoselective synthesis
Allyltitanocenes
Ketones
Peterson elimination
Conjugated dienes are useful synthetic intermediates employed
in [4+1],1 [4+2],2 [4+3],3 and other cycloadditions.2a,4 Therefore
their stereoselective preparation has been extensively studied.5
The major approaches to conjugated dienes include olefination of
unsaturated carbonyl compounds,6 enyne metathesis,7 and cou-
pling reactions of alkenylmetals with alkenyl (pseudo)halides.8
Despite the extensive studies described above, an easy access to
conjugated dienes with high stereoselectivity still remains a for-
midable challenge.
We have studied the reactions of ketones with allyltitanocenes
generated by the desulfurizative metallation of allylic sulfides with
the titanocene(II) reagent. The reaction proceeds with high stereos-
electvity9 or stereospecificity10 depending on the substitution pat-
tern of allylic sulfides. Encouraged by these results, the
diastereoselective addition of silyl group-containing allyltitanoce-
nes was examined for the diversity-oriented synthesis of b,d-11
preparation of (Z)-1,3-dienes or more highly substituted congeners
has not appeared yet.
The reductive titanation of 5a with titanocene(II)–1-butene
complex (6) was carried out in THF at 0 °C for 2 h. Subsequent
treatment of the resulting organotitanium species with 4-phenyl-
2-butenone (3a) at À78 °C for 24 h and work-up with 3 M NaOH
R
SPh
or
Cp2Ti
6
Me3Si
SPh
SiMe3
5a
5c
5b
: R = H, : R = Me
O
R
RS OH
RL
RL
RS 3
Me3Si
TiCp2SPh
and b,c
-disubstituted12 tert-homoallylic alcohols. Herein we
describe the stereoselective and operationally straightforward
method for the preparation of both (E)- and (Z)-di- and trisubsti-
tuted conjugated dienes 1 by the reaction of c-silylallyltitanocenes
2 with ketones 3 and the following Peterson elimination of the
resulting b-hydroxy silanes 4 (Scheme 1). Somfai and co-workers
reported the preparation of (E)-1-monosubstituted 1,3-dienes by
the Lewis acid-promoted reaction of 1,3-bis(silyl)propenes with
aldehydes.13 However, the application of this method to the
SiMe3
R
2a
2b
: R = H, : R = Me
4
RS
acid
RL
RL
E-1
Z-1
R
RS
base
R
Scheme 1. Stereoselective preparation of (E)- and (Z)-di- and trisubstituted 1,3-
butadienes.
⇑
Corresponding author. Tel./fax: +81 42 388 7034.
E-mail address: takeda-t@cc.tuat.ac.jp (T. Takeda).
http://dx.doi.org/10.1016/j.tetlet.2015.04.114
0040-4039/Ó 2015 Elsevier Ltd. All rights reserved.

T. Takeda et al. / Tetrahedron Letters 56 (2015) 4016–4021
4017
Table 1
Preparation of b-hydroxy silane 4a under various conditionsa
6
1) Cp2Ti(II) / THF
Me3Si
SPh
5a
and/or
OH
2) Ph(CH2)2COMe
Ph
3a
SiMe3
SPh
SiMe3 5b
3) work-up / 25 °C /
15 min
4a
Entry
5a:5b
Work-up
Yield/%b
anti:sync
1
2
3
4
5
6
90:10
90:10
90:10
90:10
0:100
47:53
3 M NaOH
H2O/THF
pH 10 Buffer/THF
Satd NH4Cl/THF
pH 10 Buffer/THF
pH 10 Buffer/THF
78
78
85
89
84
84
86:14
85:15
85:15
85:15
85:15
85:15
a
b
c
Conditions: (1) silylallyl sulfide 5 (1.25 equiv), Cp2Ti(II) 6 (2.5 equiv), 0 °C for 2 h; (2) ketone 3a (1 equiv), À78 °C for 24 h.
Isolated yield based on 3a used.
Determined by NMR spectroscopy.
produced the b-hydroxy silane 4a in 78% yield with 86% diastere-
oselectivity along with a small amount of the diene 1a (Table 1,
entry 1). The stereochemistry of the major isomer of 4a was
deduced to be anti on the basis of the stereochemistry of the diene
1a produced by the Peterson elimination under the acidic and basic
conditions described later. The stereochemical outcome of the
O
RS
SPh
R
Ti
RL
RS 3
Me3Si
H2O
Me3Si
TiCp2SPh
O
RL
2
7
R
reaction suggested that
c-(trimethylsilyl)allyltitanocene with E-
Cp
configuration 2 was stereoselectively produced and it reacted with
ketone 3 through the chair-like six-membered transition state 7 in
which the larger substituent of 3 occupied the equatorial position
(Scheme 2).
RS
TiSPh
Cp
anti-4
Me3Si
O
RL
R
To suppress the formation of 1a, the work-up conditions were
examined, and quenching with sat. NH4Cl aqueous solution
resulted in the best yield (entry 4). Since the yield and diastereos-
electivity of 4a are independent of the position of the trimethylsilyl
Scheme 2. Stereoselective formation of anti-b-hydroxy silanes 4.
Table 2
Preparation of b-hydroxy silanes 4a
1) Cp2Ti(II) 6 /
THF
SPh
SiMe3
5b
R
RS
OH
SiMe3
Me3Si
SPh
,
RL
3
2) RLCORS
R
5a: R = H, 5c: R = Me
4
3) sat. NH4Cl
3a: RL = Ph(CH2)2; RS = Me, 3b: RL = Me(CH2)10; RS = Me, 3c: RL =
3d
Me2CH(CH2)3CHMe(CH2)3; RS = Me, : RL = Ph(CH2)3; RS = Et,
3e: RL = c-Hex; RS = Me, 3f: RL = Ph(CH3)CH; RS = Me, 3g: RL
=
≡
3h
tert-Bu; RS = Ph(CH2)2C C, : RL = 4-tert-BuC6H4; RS = Me
Entry
1
5 (5a:5b)
3
4 (yield/%b; anti:sync)
OH
5a, 5b (10:90)
5a, 5b (54:46)
3a
3b
4a (89; 85:15)
4b (76; 82:18)
Ph
SiMe3
OH
2
3
SiMe3
OH
*
5a, 5b (24:76)
3c
4c (80; 82:18)d
SiMe3
(continued on next page)

4018
T. Takeda et al. / Tetrahedron Letters 56 (2015) 4016–4021
Table 2 (continued)
Entry
5 (5a:5b)
3
4 (yield/%b; anti:sync)
OH
Ph
4e
5a, 5b (22:78)
3d
4d (70; 58:42)f
4e (80; 100:0)
4f (82; 100:0)d
SiMe3
OH
5
5a, 5b (54:46)
5a, 5b (62:38)
3e
3f
SiMe3
OH
Ph
Ph
6e
*
SiMe3
OH
7
5a, 5b (24:76)
5a, 5b (24:76)
3g
3h
4g (58; 100:0)
4h (75; 100:0)
SiMe3
OH
8g
SiMe3
OH
9h
5c
5c
3a
3e
4i (75; 91:9)
4j (57; 100:0)
Ph
Ph
SiMe3
OH
10h
SiMe3
OH
11e,h
5c
3f
4k (60; 100:0)d
∗
SiMe3
a
Conditions: (1) silylallyl sulfide 5 (1.25 equiv), Cp2Ti(II) 6 (2.5 equiv), 0 °C for 2 h; (2) ketone 3 (1 equiv), À78 °C for 18-24 h; 3) 25 °C for 15 min.
Isolated yield based on 3 used.
Determined by NMR spectroscopy.
Configuration of the stereogenic center with asterisk was not necessarily determined.
Quenched with pH 10 buffer.
Ratio of diastereomers, which was determined by GC analysis.
Quenched with MeOH/hexane.
b
c
d
e
f
g
h
Preparation of 2b was carried out at À30 °C for 2 h.
Table 3
Preparation of conjugated dienes 1a
conditions A
conditions B
RS
RS
3 M H2SO4
Triton B
R
4
RL
RL
THF
MeOH, THF
R
1
1
Z-
E-
Entry
1d
4 (anti:syn)
Conditions
A
1 (yield/%b; E:Zc)
4a (86:14)
4a (85:15)
E-1a (83; 86:14)
Z-1a (87; 18:82)
Ph
Ph
2
3
4
B
A
B
4b (80:20)
4b (79:21)
E-1b (80; 83:17)
Z-1b (96; 21:79)

T. Takeda et al. / Tetrahedron Letters 56 (2015) 4016–4021
4019
Table 3 (continued)
Entry
4 (anti:syn)
4f (100:0)
Conditions
1 (yield/%b; E:Zc)
Ph
Ph
5
6
A
B
E-1c (83; 100:0)
4f (100:0)
4g (100:0)
Z-1c (86; 0:100)
Z-1d (80; 0:100)
7e
A
B
A
B
Ph
Ph
8
4g (100:0)
4h (100:0)
4h (100:0)
E-1d (86; 100:0)
E-1e (83; 100:0)
Z-1e (91; 0:100)
9d,f
10
11
12
13
4i (87:13)
4i (88:12)
4k (100:0)
4k (100:0)
A
B
A
B
E-1f (84; 91:9)
Z-1f (92; 12:88)
E-1g (56; 100:0)
Z-1g (89; 0:100)
Ph
Ph
Ph
Ph
14
a
Conditions A: 3 M H2SO4 (3.5 mL/mmol of 4), 50 °C for 1 h; conditions B: Triton B (40% in MeOH, 4-10 equiv), 25 °C for 1 h.
Isolated yield.
Determined by NMR spectroscopy.
Carried out at 25 °C.
Carried out for 8 h.
b
c
d
e
f
Carried out for 0.5 h using BF3ÁOEt2 (4.3 equiv) as an acid catalyst.
group in the allyl phenyl sulfides 5 (see entries 3, 5, and 6), a mix-
ture of 5a and 5b was conveniently employed in the following
study.
formation of pentacoordinate cyclic silicon species.14 Therefore, it
is reasonable to assume that both the (E)- and (Z)-1,1-disubstituted
or -1,1,2-trisubstituted 1,3-butadienes 1 are obtained by the
Peterson elimination of b-hydroxy silanes 4.
With the optimized reaction conditions in hand, the allylation
of a variety of ketones 3 with 5 was examined (Table 2). Similar
to the reaction of 3a, good diastereoselectivity was observed in
the reaction of methyl ketones 3b and 3c (entries 2 and 3). In con-
trast, the reaction of ethyl ketone 3d with allyltitanocene 2a pro-
duced a nearly 1:1 mixture of the diastereomers (entry 4). Only
the anti-alcohols were produced when the secondary alkyl methyl
ketones 3e and f were employed (entries 5 and 6). The anti-isomers
were also obtained as sole products by the reaction of alkynyl
ketone 3g (entry 7) and aromatic ketone 3h (entry 8). It is of special
note that the homoallylic alcohols bearing two adjacent quaternary
Indeed, the treatment of 4a with 3 M H2SO4 in THF at 25 °C for
1 h produced the E-diene E-1a without the loss of stereoisomeric
purity (Table 3, entry 1). Under basic conditions using Triton B,
in contrast, 4a was transformed into the (Z)-diene Z-1a with
almost the same stereoselectivity (entry 2). These results indicate
that the Peterson elimination proceeded with complete stere-
ospecificity. The stereoisomerically pure alcohols 4f–h were trans-
formed into both the (E)- and (Z)-dienes 1 by similar treatment
with acid or base with complete stereoselectivity (entries 5–
10).15 The trisubstituted butadienes 1f and g were also obtained
with high stereoselectivity by the treatment of highly substituted
b-hydroxy silanes 4i and k (entries 11–14).
carbons were produced with high diastereoselectivity using
c-
(trimethylsilyl)crotyl sulfide 5c (entries 9–11).
It is well known that the Peterson elimination is a highly
stereoselective process. Under acidic conditions, b-hydroxy silanes
provide the alkenes by an anti-elimination pathway. Conversely,
syn-elimination proceeds under basic conditions through the
To simplify the procedure for the synthesis of dienes 1, a ‘one-
pot reaction’ was examined in several cases (Table 4). After the
reaction of allyltitanocene 2a with 4-phenyl-2-butanone (3a), a
methanol solution of Triton B was added to the reaction mixture

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T. Takeda et al. / Tetrahedron Letters 56 (2015) 4016–4021
Table 4
One-pot transformation of ketones 3 into conjugated dienes 1a
RS
RS
1
E-
Me3Si
SPh
5a
RL
RL
6
1) Cp2Ti(II) / THF
R
2) RLCORS
3
and
SPh
3) reagent
R
1
Z-
SiMe3 5b
Entry
5 (5a:5b)
3
Product 1 (reagent)
Yield/%b; E:Zc
d
1
2
3
4
5a, 5b (32:68)
5a, 5b (62:38)
5a, 5b (32:68)
5a, 5b (66:34)
3a
3a
3b
3b
E-1a (BF3ÁOEt2
Z-1a (Triton B)
E-1b (BF3ÁOEt2)
Z-1b (Triton B)
)
71; 84:16
86; 19:81
61; 88:12
77; 17:83
5
6
5a, 5b (67:33)
3c
3c
49; 86:14
E-1h
(BF3·OEt2)
5a, 5b (67:33)
67; 25:75
Z-1h
(Triton B)
7e
8
5a, 5b (32:68)
5a, 5b (61:39)
3f
3f
E-1c (BF3ÁOEt2)
63; 100:0
83; 0:100
Z-1c (Triton B)
a
Conditions: (1) silylallyl sulfide 5 (1.25 equiv), Cp2Ti(II) 6 (2.5 equiv), 0 °C for 2 h; (2) ketone 3 (1 equiv), À78 °C for 18–24 h.; (3) BF3ÁOEt2 (8 equiv), 25 °C for 1 h or Triton
B (40% in MeOH, 9 equiv), 25 °C for 1 h.
b
Isolated yield based on 3 used.
Determined by NMR spectroscopy.
c
d
BF3ÁOEt2 (16 equiv) was used.
e
Peterson elimination was carried out at reflux for 5 h.
Suginome, M. J. Am. Chem. Soc. 2009, 131, 16624–16625; (d) Wu, Q.; Hu, J.; Ren,
X.; Zhou, J. S. Chem. Eur. J. 2011, 17, 11553–11558.
at À78 °C and the mixture was stirred at 25 °C for 1 h to afford the
(Z)-diene Z-1a with stereoselectivity comparable to that of the
stepwise process (entry 2). Using the same procedure, the (Z)-di-
enes Z-1b, c, and h (entries 4, 6, 8) were obtained. By contrast,
the one-pot Peterson elimination of b-hydroxy silane 4a under
acidic conditions using H2SO4 was unsuccessful and a substantial
amount of 4a remained unchanged. After several attempts,
BF3ÁOEt2 was found to be the best promoter for the one-pot trans-
formation of 3 to E-1 (entries 1, 3, 5, and 7).
In conclusion, we have established a versatile method for the
stereoselective preparation of both (E)- and (Z)-di- and trisubsti-
tuted 1,3-butadienes. These unsaturated compounds are useful
motifs for the construction of a variety of cyclic compounds
through cycloadditions. Further extension of this method to the
preparation of more highly substituted 1,3-butadienes is currently
under way.
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Supplementary data
Supplementary data (experimental procedures and full charac-
terization of sillyl sulfides and all products) associated with this
article can be found, in the online version, at http://dx.doi.org/10.
1016/j.tetlet.2015.04.114.
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