A facile method for the stereoselective preparation of (1Z,3E)-dienyl ethers via 1,4-elimination of 1,4-dialkoxy-(2Z)-alkenes with n-butyllithium

Article abstract of DOI:10.1055/s-2006-939053

Treatment of 1-alkoxy-4-methoxy-(2Z)-alkenes or 1-siloxy-4-methoxy-(2Z)- alkenes with n-butyllithium in diethyl ether is shown to afford the corresponding (1Z,3E)-dienyl, alkyl or silyl ethers, respectively, in high stereoselectivity via a facile 1,4-elim

Full text of DOI:10.1055/s-2006-939053

LETTER
849
A Facile Method for the Stereoselective Preparation of (1Z,3E)-Dienyl Ethers
via 1,4-Elimination of 1,4-Dialkoxy-(2Z)-alkenes with n-Butyllithium
Stereoselective
i
P
repara
j
tion of
i
(1
Z
,3
E
)-Die
T
nyl Ethers ayama,* Sayaka Sugai
Graduate School of Science and Technology, Niigata University, Niigata 950-2181, Japan
Fax +81(25)2627741; E-mail: tayama@gs.niigata-u.ac.jp
Received 26 December 2005
methoxy- and 1,4-dialkoxy-(2Z)-alkenes with n-butyl-
lithium and the scope and stereochemical feature thereof
(Scheme 2).
Abstract: Treatment of 1-alkoxy-4-methoxy-(2Z)-alkenes or 1-sil-
oxy-4-methoxy-(2Z)-alkenes with n-butyllithium in diethyl ether is
shown to afford the corresponding (1Z,3E)-dienyl, alkyl or silyl
ethers, respectively, in high stereoselectivity via a facile 1,4-elimi-
nation. The scope and the regio- and stereochemical features of the
synthetic method are described.
n-BuLi
R
PO
OCH3
Et2O
PO
(1Z,3E)-2
R
Key words: 1,4-eliminations, dienyl ethers, dienyl acetals, stereo-
selective synthesis, precoordinations
1
P = SiR3, MOM, EE, THP, etc.
R = H, n-Bu, OCH3
Scheme 2
In the course of studies on the Wittig1 and retro-Brook1a
rearrangement of allylic ether systems, it occurred to us
that when 4-methoxy-(2Z)-butenyl tert-butyldimethyl-
silyl ether (1a) was treated with n-butyllithium (1.5 equiv)
in diethyl ether, the (1Z,3)-butadienyl silyl ether (2a) was
formed in 70% yield as a single stereoisomer without any
concomitant formation of possible by-products such as
the other dienyl ether 2a¢, the [1,2] retro-Brook product
3a, and the [1,2] Wittig product 4a (Scheme 1).
As already mentioned, we found that silyl ether 1a was
treated with n-BuLi in diethyl ether at –20 °C for two
hours gave the (1Z,3)-dienyl silyl ether 2a as a single
stereoisomer in 70% yield (Table 1, entry 1). The Z-geo-
1
metry was assigned by H NMR assay (J1H,2H = 5.9 Hz).
Apparently, this reaction can be considered as a 1,4- (or
vinylogous 1,2-) elimination process. Of special interest is
that the initial deprotonation occurs on the siloxy-bearing
methylene in preference to the methoxy-bearing methyl-
ene to liberate methanol. To examine the stereoselectivity
on the olefinic bond formed at the 3-position, 4-butyl-sub-
stituted substrate (1b, R = n-Bu)9 was reacted with n-BuLi
under the same conditions. Interestingly enough, the di-
enyl silyl ether 2b was obtained almost exclusively as the
1Z,3E isomer in 88% yield (entry 2).10 The stereochemis-
try was determined by 1H NMR assay (J1H,2H = 5.9 Hz and
n-BuLi
tBuMe2SiO
OCH3
Et2O
–20 °C
t
OSiMe2 Bu
1a
(1Z, 3)-2a
tBuMe2SiO
OH
CH3
HO
OCH3
t
OCH3
SiMe2 Bu
2a'
3a
4a
J
3H,4H = 15.6 Hz). Equally high stereoselectivities were
Scheme 1
observed in similar reactions of 4-methoxy-substituted
substrate (1c, entry 3). To further expand the scope of the
present 1,3-dienyl ether forming reaction, we prepared a
series of O-protected ethers 1d–h11 and carried out their
reactions with n-butyllithium under the same conditions
(entries 4–8). Significantly, the reaction of the EE-pro-
tected substrate 1d gave the (1Z,3E)-dienyl ether 2d in a
high stereoselectivity, while the reactions of other O-pro-
tected substrates also showed a high 1Z-stereoselectivity.
Thus, these O-protected 1,3-dienyl ethers might find
unique synthetic applications, since easy deprotection af-
ter synthetic transformations should impart a hydroxyl
functionality to the products. Interestingly, this reaction is
applicable to the preparation of the 1,3,5-trienyl ether. For
instance, a similar reaction of 1i afforded the (1Z,3E,5)-
trienyl ether 2i in 53% yield as depicted in Scheme 3.
Prompted by this rather unexpected observation, we de-
cided to investigate the scope and limitation of this type of
1,3-dienyl ether forming reaction in view of the synthetic
potentiality of 1,3-dienyl ethers, e.g., as dienolate equiva-
lents for aldol-type2 and Ferrier-type reactions3 or as diene
components for the Diels–Alder reactions.4 While several
1,3-dienyl ethers have been prepared via O-silylation or
O-alkylation of the dienolates derived from a,b-unsaturat-
ed carbonyl compounds, the stereoselectivities of this
conventional method are generally unsatisfactory and its
scope remains limited in terms of the kind of introducible
O-alkyl substituents.5–7 Described herein are a facile and
stereoselective synthetic method for various types of
(1Z,3E)-dienyl ethers via 1,4-elimination8 of 1-siloxy-4-
One remarkable feature of the present dienyl ether form-
ing reaction is that various types of (1Z,3)- and (1Z,3E)-
dienyl ethers can be obtained in high stereoselectivities.
SYNLETT 2006, No. 6, pp 0849–0852
Advanced online publication: 14.03.2006
DOI: 10.1055/s-2006-939053; Art ID: U32105ST
© Georg Thieme Verlag Stuttgart · New York
0
4.
0
4.
2
0
0
6

850
E. Tayama, S. Sugai
LETTER
Table 1 The Reactions of Ether 1 with n-BuLi12
Entry
Substratea
Temp (°C)
Time (h)
Product
2a
Yield (%)b
(1Z,3E)/other isomersc
1
2
3
4
5
6
7
8
1a (P = SiMe2t-Bu, R = H)
1b (P = SiMe2t-Bu, R = n-Bu)
1c (P = SiMe2t-Bu, R = OCH3)
1d (P = EE, R = n-Bu)
1e (P = MOM, R = n-Bu)
1f (P = BOM, R = n-Bu)
1g (P = MIP, R = n-Bu)
1h (P = THP, R = n-Bu)
–20
–20
–40
–20
0
2
70d
88
96d
89
66
74
83
73
>98:2
>98:2
>98:2
93:7
4
2b
2
2c
2.5
3.5
3
2d
2e
94:6
–20
0
2f
97:3
3
2g
>98:2
90:10
0
4
2h
a EE = 1-ethoxyethyl; MOM = methoxymethyl; BOM = benzyloxymethyl; MIP = methoxyisopropyl; THP = 2-tetrahydropyranyl.
b Isolated yield of the stereoisomeric mixture.
c Determined by 1H NMR analysis.
d Determined by 1H NMR assay using mesitylene as an internal standard.
n-BuLi
n-BuLi
(1Z,3E)/(1Z,3Z)/(1E,3E)/(1E,3Z)
EEO
OCH3
tBuMe2SiO
OCH3
–20 °C
2.5 h
nBu
t
Et2O
–40 °C, 3 h
–20 °C, 2 h
OSiMe2 Bu
in Et2O (%) = 82:0:4:3
in THF (%) = 4:0:39:38
1d
1i
(1Z,3E,5)-2i
nBu
EEO
nBu
EEO
Scheme 3
nBu
nBu
OEE
OEE
(1E,3E)
(1E,3Z)
(1Z,3E)
(1Z,3Z)
The high stereoselectivity, though its exact origin is un-
clear at present, might be rationalized as a result of the
precoordination of the n-butyllithium to the both ether
oxygens to form complex A which should be sterically
favored over complex B. The complex A leads to the
1Z,3E isomer and the complex B leads to the 1Z,3E or
1Z,3Z isomers (Figure 1).13
Scheme 4
EEO
n-BuLi
(1Z,3E)/(1Z,3Z)/(1E,3E)/(1E,3Z)
–20 °C
2.5 h
OCH3
in Et2O (%) = 34:23:2:1
in THF (%) = 48:36:3:3
nBu
(E)-1d
H
R
H
H
Scheme 5
O
O
O
O
R
CH3
H
P
H
CH3
H
P
Li
Li
In summary, we have demonstrated that simple treatment
of 1-siloxy-4-methoxy- and 1-alkoxy-4-methoxy-(2Z)-
alkenes with n-butyllithium in diethyl ether affords the
corresponding 1,3-dienyl ethers as the 1Z,3E-form in high
stereoselectivity. Furthermore, the interesting regio- and
stereochemical features of the dienyl ether forming 1,4-
elimination reaction are revealed. The synthetic applica-
tion of the conjugated dienyl ethers thus obtained is
underway in our laboratory.
Bu
Bu
A
B
(1Z,3E)
(1Z,3E) or (1Z,3Z)
Figure 1
In fact, when a similar reaction of 1d was carried out in
THF which might suppress the aforementioned precoordi-
nation, the dienyl ether was obtained as a 1:1 mixture of
the 1E,3E and 1E,3Z isomer, together with 4% of 1Z,3E
isomer in 81% combined yield, respectively (Scheme 4).
The observed 1Z-to-1E changeover is surprising, while its
mechanistic origin is presently unclear.14 More interest-
ingly, a similar reaction of the 2E counterpart of 1d in di-
ethyl ether, wherein the aforementioned bidentate
precoordination is impossible, was found to give a 1.5:1
mixture of the 1Z,3E and 1Z,3Z isomer, along with 3% of
other isomers in 60% combined yield (Scheme 5). In this
E-substrate case, switch of the solvent to THF provided
nearly identical stereoisomeric ratios.15
References and Notes
(1) For reviews, see: (a) Tomooka, K. In The Chemistry of
Organolithium Compounds, Vol. 2; Rappoport, Z.; Marek,
I., Eds.; John Wiley and Sons Ltd.: Chichester, 2004, 749–
828. (b) Clayden, J. In Organolithiums: Selectivity for
Synthesis; Baldwin, J. E.; Williams, R. M., Eds.; Pergamon:
Manchester, 2002, Chap. 8. (c) Tomooka, K.; Yamamoto,
H.; Nakai, T. Liebigs Ann./Recl. 1997, 1275. (d) Nakai, T.;
Mikami, K. Org. React. 1994, 46, 105. (e) Brückner, R. In
Comprehensive Organic Synthesis, Vol. 6; Trost, B. M.;
Fleming, I., Eds.; Pergamon: Oxford, 1991, Chap. 4.6.
Synlett 2006, No. 6, 849–852 © Thieme Stuttgart · New York

LETTER
Stereoselective Preparation of (1Z,3E)-Dienyl Ethers
851
(2) (a) Casiraghi, G.; Zanardi, F.; Appendino, G.; Rassu, G.
Chem. Rev. 2000, 100, 1929. (b) Ishida, A.; Mukaiyama, T.
Bull. Chem. Soc. Jpn. 1977, 50, 1161.
1470, 1406, 1362, 1334, 1254, 1190, 1092, 1006, 956, 912,
838, 776 cm–1. Anal. Calcd for C11H24O2Si: C, 61.05; H,
11.18. Found: C, 61.17; H, 11.48.
(3) (a) Inui, M.; Hosokawa, S.; Nakazaki, A.; Kobayashi, S.
Tetrahedron Lett. 2005, 46, 3245. (b) Suzuki, T.; Inui, M.;
Hosokawa, S.; Kobayashi, S. Tetrahedron Lett. 2003, 44,
3713.
(4) Danishefsky, S.; Kitahara, T. J. Am. Chem. Soc. 1974, 96,
7807.
(2Z)-1-(Benzyloxymethoxy)-4-methoxy-2-octene (1f)
Colorless oil. 1H NMR (270 MHz, CDCl3): d = 7.40–7.27 (5
H, m, Ph), 5.82–5.72 (1 H, m, 2-H), 5.49–5.39 (1 H, m, 3-H),
4.78 (2 H, s, OCH2O), 4.62 (2 H, s, OCH2Ph), 4.27 (1 H, ddd,
J = 12.4, 7.3, 1.4 Hz, 1-CH2), 4.15 (1 H, ddd, J = 12.4, 6.1,
1.4 Hz, 1-CH2), 3.94–3.85 (1 H, m, 4-H), 3.25 (3 H, s,
OCH3), 1.68–1.52 (1 H, m, 5-CH2), 1.47–1.18 (5 H, m, 5-,
6-, and 7-CH2), 0.88 (3 H, t, J = 6.8 Hz, 8-CH3). 13C NMR
(68 MHz, CDCl3): d = 137.6, 134.2, 128.7, 128.3, 127.7,
127.6, 93.8, 76.6, 69.3, 63.2, 56.1, 35.2, 27.4, 22.7, 14.1. IR
(film): 3060, 3024, 2928, 2872, 2816, 1496, 1454, 1402,
1380, 1206, 1190, 1168, 1102, 1048, 962, 958, 736, 698
cm–1. Anal. Calcd for C17H26O3: C, 73.34; H, 9.41. Found: C,
73.42; H, 9.63.
(5) For a review of 1,3-dienyl silyl ethers (silyl dienol ethers),
see: Brownbridge, P. Synthesis 1983, 85.
(6) Previous preparation of 1,3-dienyl silyl ethers: (a) Choi, J.;
Imai, E.; Mihara, M.; Oderaotoshi, Y.; Minakata, S.;
Komatsu, M. J. Org. Chem. 2003, 68, 6164. (b) Janey, J.
M.; Iwama, T.; Kozmin, S. A.; Rawal, V. H. J. Org. Chem.
2000, 65, 9059. (c) Moreno, M. J. S. M.; Martins, R. M. L.
M.; Melo, M. L. S.; Neves, A. S. C. Chem. Lett. 1997, 529.
(d) Tominaga, Y.; Kamio, C.; Hosomi, A. Chem. Lett. 1989,
1761. (e) Iqbal, J.; Khan, M. A. Synth. Commun. 1989, 19,
515. (f) Cazeau, P.; Duboudin, F.; Moulines, F.; Babot, O.;
Dunogues, J. Tetrahedron 1987, 43, 2089. (g) Colvin, E.
W.; Thom, I. G. Tetrahedron 1986, 42, 3137. (h) Casey, C.
P.; Jones, C. R.; Tukada, H. J. Org. Chem. 1981, 46, 2089.
(i) Hirai, K.; Suzuki, H.; Morooka, Y.; Ikawa, T.
Tetrahedron Lett. 1980, 21, 3413. (j) Miller, R. D.;
McKean, D. R. Synthesis 1979, 730. (k) House, H. O.;
Czuba, L. J.; Gall, M.; Olmstead, H. D. J. Org. Chem. 1969,
34, 2324.
(7) Previous preparation of alkyl 1,3-dienyl ethers: (a) Gilbert,
J. C.; Weerasooriya, U. J. Org. Chem. 1983, 48, 448.
(b) Hiranuma, H.; Miller, S. I. J. Org. Chem. 1982, 47,
5083. (c) Dowd, P.; Weber, W. J. Org. Chem. 1982, 47,
4774. (d) Kluge, A. F.; Cloudsdale, I. S. J. Org. Chem. 1979,
44, 4847. (e) Earnshaw, C.; Wallis, C. J.; Warren, S. J.
Chem. Soc., Perkin Trans. 1 1979, 3099.
(1Z)-1-(tert-Butyldimethylsilyloxy)-1,3-butadiene (2a)16
Colorless oil; purified by chromatography on silica gel
(hexane–Et2O = 100:1 to 20:1 as eluent). 1H NMR (270
MHz, CDCl3): d = 6.76 (1 H, dddd, J = 17.3, 10.7, 10.3, 1.1
Hz, 3-H), 6.19 (1 H, ddd, J = 5.9, 1.1, 1.1 Hz, 1-H), 5.20 (1
H, dd, J = 10.7, 5.9 Hz, 2-H), 5.07 (1 H, m, J = 17.3, 2.0 Hz,
4cis-H), 4.89 (1 H, ddd, J = 10.3, 2.0, 1.1 Hz, 4trans-H), 0.94
[9 H, s, SiC(CH3)3], 0.16 [6 H, s, Si(CH3)2]. 13C NMR (68
MHz, CDCl3): d = 140.4, 129.8, 112.9, 111.1, 25.7, 18.4,
–5.3. IR (film): 3080, 2952, 2928, 2884, 2856, 1642, 1594,
1472, 1438, 1392, 1362, 1254, 1174, 1080, 998, 928, 890,
840, 784 cm–1.
(1Z,3E)-1-(tert-Butyldimethylsilyloxy)-1,3-octadiene (2b)
Colorless oil; purified by chromatography on silica gel
(hexane–EtOAc = 100:1 as eluent). 1H NMR (270 MHz,
CDCl3): d = 6.40 (1 H, ddd, J = 15.6, 10.8, 1.1 Hz, 3-H), 6.09
(1 H, d, J = 5.9 Hz, 1-H), 5.55 (1 H, dt, J = 15.6, 6.8 Hz, 4-
H), 5.13 (1 H, dd, J = 10.8, 5.9 Hz, 2-H), 2.14–2.02 (2 H, dt,
J = 6.8, 6.8 Hz, 5-CH2), 1.44–1.24 (4 H, m, 6-CH2 and 7-
CH2), 0.94 [9 H, s, SiC(CH3)3], 0.89 (3 H, t, J = 7.0 Hz, 8-
CH3), 0.15 [6 H, s, Si(CH3)2]. 13C NMR (68 MHz, CDCl3):
d = 138.2, 130.9, 122.8, 110.8, 32.7, 31.8, 25.7, 22.4, 18.4,
14.1, –5.2. IR (film): 3028, 2952, 2924, 2852, 1654, 1612,
1470, 1410, 1362, 1254, 1156, 1112, 1050, 1006, 972, 838,
780 cm–1. Anal. Calcd for C14H28OSi: C, 69.93; H, 11.74.
Found: C, 69.70; H, 12.03.
(8) A similar type of 1,4-elimination reaction has been reported
using alkenyl acetals: Canepa, C.; Prandi, C.; Sacchi, L.;
Venturello, P. J. Chem. Soc., Perkin Trans. 1 1993, 1875.
(9) Prepared in three steps: (i) t-BuMe2SiOCH2C≡CH, n-BuLi,
THF, –78 °C then n-BuCHO, –78 °C to r.t.; (ii) NaH, MeI,
THF, 0 °C to r.t.; (iii) H2 (1 atm), 5% Lindlar cat., quinoline,
MeOH, r.t.
(10) All stereoisomers were identified by 1H NMR comparisons
of the authentic samples prepared from (EtO)2P(O)CH2OP
via the literature procedure (ref. 7d).
(1Z,3E)-1-(tert-Butyldimethylsilyloxy)-4-methoxy-1,3-
butadiene (2c)
(11) Prepared from POCH2C≡CH according to the same three-
Pale yellow oil; purified by chromatography on silica gel
(hexane–Et2O = 30:1 as eluent). 1H NMR (270 MHz,
CDCl3): d = 6.55 (1 H, d, J = 13.0 Hz, 4-H), 6.06 (1 H, d,
J = 5.9 Hz, 1-H), 5.84 (1 H, dd, J = 13.0, 10.8 Hz, 3-H), 5.05
(1 H, dd, J = 10.8, 5.9 Hz, 2-H), 3.59 (3 H, s, OCH3), 0.94 [9
H, s, SiC(CH3)3], 0.15 [6 H, s, Si(CH3)2]. 13C NMR (68
MHz, CDCl3): d = 148.2, 136.6, 106.5, 98.9, 56.2, 25.7,
18.4, –5.2. IR (film): 2948, 2928, 2892, 2852, 1656, 1608,
1470, 1406, 1362, 1332, 1256, 1208, 1166, 1136, 1124,
1064, 938, 838, 780 cm–1. Anal. Calcd for C11H22O2Si: C,
61.63; H, 10.34. Found: C, 61.58; H, 10.61.
step procedure as described for 1b (ref. 9).
(12) Typical Procedure for the Preparation of 1,3-Dienyl
Ethers 2
To a solution of 1 (1.0 equiv, 0.25 M) in Et2O was added a
1.6 M n-BuLi solution in n-hexane (1.5 equiv) at –40 °C to
0 °C and the mixture was stirred for 2–4 h at the same
temperature. The resulting mixture was quenched with H2O
and extracted with Et2O. The combined extract was washed
with brine, dried over NaSO4 and concentrated. The residue
was purified by chromatography on silica gel to afford the
corresponding 1,3-dienyl ether 2.
(1Z,3E)-1-(1-Ethoxyethoxy)-1,3-octadiene (2d)
Selected Spectroscopic Data
(2Z)-1-(tert-Butyldimethylsilyloxy)-4-methoxy-2-butene
(1a)
Pale yellow oil; purified by chromatography on silica gel
(hexane–EtOAc = 70:1 to 40:1 as eluent). 1H NMR (270
MHz, CDCl3): d = 6.39 (1 H, ddd, J = 15.4, 10.8, 1.4 Hz, 3-
H), 6.12 (1 H, d, J = 5.9 Hz, 1-H), 5.57 (1 H, dt, J = 15.4, 7.0
Hz, 4-H), 5.12 (1 H, dd, J = 10.8, 5.9 Hz, 2-H), 4.94 (1 H, q,
J = 5.4 Hz, OCHO), 3.74 (1 H, dq, J = 9.5, 7.2 Hz,
OCH2CH3), 3.49 (1 H, dq, J = 9.5, 7.2 Hz, OCH2CH3), 2.12–
2.04 (2 H, dt, J = 7.0, 6.8 Hz, 5-CH2), 1.43–1.25 (4 H, m, 6-
CH2 and 7-CH2), 1.39 [3 H, d, J = 5.4 Hz, OCH(CH3)O],
1.21 (3 H, t, J = 7.2 Hz, OCH2CH3), 0.89 (3 H, t, J = 7.0 Hz,
Colorless oil. 1H NMR (270 MHz, CDCl3): d = 5.70 (1 H,
dtt, J = 11.1, 5.9, 1.4 Hz, 2- or 3-H), 5.57 (1 H, dtt, J = 11.1,
5.9, 1.4 Hz, 2- or 3-H), 4.24 (1 H, dd, J = 5.9, 1.4 Hz, 1-H),
3.99 (1 H, dd, J = 5.9, 1.4 Hz, 4-H), 3.33 (3 H, s, OCH3),
0.90 [9 H, s, SiC(CH3)3], 0.07 [6 H, s, Si(CH3)2]. 13C NMR
(68 MHz, CDCl3): d = 132.6, 126.7, 68.3, 59.5, 58.0, 26.0,
18.4, –5.0. IR (film): 3020, 2948, 2924, 2884, 2852, 1475,
Synlett 2006, No. 6, 849–852 © Thieme Stuttgart · New York

852
E. Tayama, S. Sugai
LETTER
8-CH3). 13C NMR (68 MHz, CDCl3): d = 138.9, 131.5,
122.8, 108.1, 100.9, 62.5, 32.7, 31.8, 22.4, 20.6, 15.2, 14.0.
IR (film): 3036, 2956, 2924, 2872, 1656, 1618, 1444, 1382,
1342, 1276, 1226, 1150, 1134, 1112, 1080, 1052, 974, 880,
830, 748 cm–1. Anal. Calcd for C12H22O2: C, 72.68; H, 11.18.
Found: C, 72.52; H, 11.47.
(1Z,3E)-1-(Methoxymethoxy)-1,3-octadiene (2e)
Colorless oil; purified by chromatography on silica gel
(hexane–EtOAc = 70:1 to 40:1 as eluent). 1H NMR (270
MHz, CDCl3): d = 6.39 (1 H, ddd, J = 15.5, 10.9, 1.1 Hz, 3-
H), 6.03 (1 H, d, J = 6.2 Hz, 1-H), 5.60 (1 H, dt, J = 15.5, 7.0
Hz, 4-H), 5.17 (1 H, dd, J = 10.9, 6.2 Hz, 2-H), 4.83 (2 H, s,
OCH2O), 3.42 (3 H, s, OCH3), 2.16–2.02 (2 H, dt, J = 7.0,
6.8 Hz, 5-CH2), 1.45–1.23 (4 H, m, 6-CH2 and 7-CH2), 0.90
(3 H, t, J = 7.0 Hz, 8-CH3). 13C NMR (68 MHz, CDCl3): d =
141.2, 132.2, 122.4, 108.9, 96.4, 55.8, 32.7, 31.7, 22.4, 14.1.
IR (film): 3036, 2952, 2920, 1658, 1618, 1464, 1386, 1306,
1242, 1160, 1114, 1042, 974, 924, 830, 750 cm–1. Anal.
Calcd for C10H18O2: C, 70.55; H, 10.66. Found: C, 70.38; H,
10.75.
IR (film): 3032, 2988, 2952, 2924, 2852, 1656, 1616, 1464,
1402, 1374, 1264, 1218, 1184, 1138, 1106, 1072, 1032, 974,
868, 782, 750 cm–1. Anal. Calcd for C12H22O2: C, 72.68; H,
11.18. Found: C, 72.55; H, 11.44.
(1Z,3E)-1-(2-Tetrahydropyranyloxy)-1,3-octadiene (2h)
Pale yellow oil; purified by chromatography on silica gel
(hexane–EtOAc = 70:1 to 40:1 as eluent). 1H NMR (270
MHz, CDCl3): d = 6.42 (1 H, ddd, J = 15.5, 10.9, 0.8 Hz, 3-
H), 6.10 (1 H, d, J = 5.9 Hz, 1-H), 5.59 (1 H, dt, J = 15.5, 7.3
Hz, 4-H), 5.16 (1 H, dd, J = 10.9, 5.9 Hz, 2-H), 4.94 (1 H, t,
J = 3.1 Hz, OCHO), 3.85 (1 H, ddd, J = 11.2, 9.5, 3.5 Hz,
THP-6-CH2), 3.62–3.52 (1 H, m, THP-6-CH2), 2.16–2.04 (2
H, dt, J = 7.3, 6.8 Hz, 5-CH2), 1.99–1.11 (10 H, m, THP-
3,4,5-CH2 and 6,7-CH2), 0.90 (3 H, t, J = 7.3 Hz, 8-CH3). 13C
NMR (68 MHz, CDCl3): d = 140.8, 131.8, 122.6, 108.4,
98.5, 61.9, 32.7, 31.8, 29.7, 25.2, 22.4, 18.7, 14.1. IR (film):
3032, 2946, 2924, 2868, 1658, 1618, 1454, 1356, 1242,
1202, 1124, 1028, 970, 904, 872, 816, 750 cm–1. Anal. Calcd
for C13H22O2: C, 74.24; H, 10.54. Found: C, 74.25; H, 10.78.
(1Z,3E)-1-(tert-Butyldimethylsilyloxy)-6-methyl-1,3,5-
heptatriene (2i)
(1Z,3E)-1-(Benzyloxymethoxy)-1,3-octadiene (2f)
Colorless oil; purified by chromatography on silica gel
(hexane–EtOAc = 80:1 to 50:1 as eluent). 1H NMR (270
MHz, CDCl3): d = 7.37–7.27 (5 H, m, Ph), 6.40 (1 H, ddd,
J = 15.4, 10.8, 1.1 Hz, 3-H), 6.10 (1 H, d, J = 6.2 Hz, 1-H),
5.61 (1 H, dt, J = 15.4, 7.0 Hz, 4-H), 5.19 (1 H, dd, J = 10.8,
6.2 Hz, 2-H), 4.95 (2 H, s, OCH2O), 4.65 (2 H, s, OCH2Ph),
2.16–2.06 (2 H, dt, J = 7.0, 6.8 Hz, 5-CH2), 1.45–1.25 (4 H,
Colorless oil; purified by chromatography on silica gel
(hexane–Et2O = 50:1 to 20:1 as eluent). 1H NMR (270 MHz,
CDCl3): d = 6.48 (1 H, dd, J = 15.1, 10.5 Hz, 3-H), 6.30 (1
H, dd, J = 15.1, 10.8 Hz, 4-H), 6.17 (1 H, d, J = 5.7 Hz, 1-
H), 5.93–5.86 (1 H, m, 5-H), 5.24 (1 H, dd, J = 10.5, 5.7 Hz,
2-H), 1.79 [3 H, s, C(CH3)2], 1.76 [3 H, s, C(CH3)2], 0.94 [9
H, s, SiC(CH3)3], 0.16 [6 H, s, Si(CH3)2]. 13C NMR (68
MHz, CDCl3): d = 139.5, 134.0, 125.9, 125.6, 123.2, 111.3,
26.2, 25.7, 18.4, –5.2. IR (film): 3028, 2952, 2924, 2856,
1646, 1628, 1584, 1470, 1408, 1274, 1256, 1236, 1140,
1066, 1032, 1006, 986, 964, 838, 780 cm–1. Anal. Calcd for
C14H26OSi: C, 70.52; H, 10.99. Found: C, 70.78; H, 11.23.
(13) Use of s-BuLi or t-BuLi in Et2O instead of n-BuLi gave the
same results, which suggests that the aggregation states of n-
BuLi under our reaction conditions are monomer or dimer,
since t-BuLi becomes dimeric in Et2O without substrates.
(14) The complete 1Z-to-1E changeover was observed in the case
of 1d. The reaction of silyl derivative 1b in THF under the
same conditions gave a mixture of stereoisomers without
any detectable retro-Brook rearrangement product:
m, 6-CH2 and 7-CH2), 0.90 (3 H, t, J = 7.0 Hz, 8-CH3). 13
NMR (68 MHz, CDCl3): d = 141.2, 137.0, 132.2, 128.3,
C
128.0, 127.8, 122.4, 109.0, 94.3, 69.8, 32.7, 31.7, 22.4, 14.1.
IR (film): 3032, 2952, 2924, 2868, 1658, 1618, 1496, 1454,
1380, 1300, 1226, 1172, 1116, 1042, 974, 904, 832, 744, 696
cm–1. Anal. Calcd for C16H22O2: C, 78.01; H, 9.00. Found: C,
78.16; H, 9.21.
(1Z,3E)-1-(1-Methoxy-1-methylethoxy)-1,3-octadiene
(2g)
Pale yellow oil; purified by chromatography on silica gel
(hexane–EtOAc = 80:1 to 60:1 as eluent). 1H NMR (270
MHz, C6D6): d = 6.83 (1 H, ddd, J = 15.5, 10.7, 1.1 Hz, 3-H),
6.32 (1 H, d, J = 6.2 Hz, 1-H), 5.61 (1 H, dt, J = 15.5, 7.0 Hz,
4-H), 5.30 (1 H, dd, J = 10.7, 6.2 Hz, 2-H), 3.01 (3 H, s,
OCH3), 2.13–2.01 (2 H, dt, J = 7.0, 6.5 Hz, 5-CH2), 1.38–
1.15 [10 H, m, OC(CH3)2O and 6, 7-CH2], 0.81 (3 H, t,
J = 7.0 Hz, 8-CH3). 13C NMR (68 MHz, C6D6): d = 137.0,
131.0, 124.2, 108.9, 101.9, 48.9, 33.2, 32.3, 25.0, 22.8, 14.3.
(1Z,3E)/(1Z,3Z)/(1E,3E)/(1E,3Z) = 42:1:16:21 (yield, %).
(15) Use of TMEDA–Et2O instead of THF gave almost the same
results.
(16) Hartung, J.; Kneuer, R. Eur. J. Org. Chem. 2000, 1677.
Synlett 2006, No. 6, 849–852 © Thieme Stuttgart · New York