Synthesis of symmetrical and unsymmetrical 2,5-bis(trialkylsilyl)furans and 2,6-bis(trialkylsilyl)-4H-pyrans from 1,4- and 1,5-bis(acylsilanes)

Article abstract of DOI:10.1055/s-2000-6284

2,5-Bis(trialkylsilyl)furans and 2,6-bis(trialkylsilyl)-4Hpyrans have been synthesized by cyclodehydration of 1,4- and 1,5-bis(acylsilanes) under p-toluenesulfonic acid catalysis. The 1,4-bis(acylsilanes) have been prepared from 1,2-bis(1,3-dithian-2yl)ethane according to the reaction sequence metallation-silylationdethioketalization. The 1,5-bis(acylsilanes) have been prepared from 1,3-bis(1,3-dithian-2-yl)propane by a similar strategy or from a S(N) reaction of 1,3-dihalopropanes with 2-trialkylsilyl-2-lithio- 1,3dithiane and deprotection. The method allows efficient preparation of symmetrical as well as unsymmetrical bis(silylated) heterocycles.

Full text of DOI:10.1055/s-2000-6284

PAPER
843
Synthesis of Symmetrical and Unsymmetrical 2,5-Bis(trialkylsilyl)furans and
2,6-Bis(trialkylsilyl)-4H-pyrans from 1,4- and 1,5-Bis(acylsilanes)
Jean-Philippe Bouillon,* Damien Saleur, Charles Portella*
Laboratoire "Réactions Sélectives et Applications," Associé au CNRS (UMR 6519), Université de Reims, Faculté des Sciences B.P. 1039,
F-51687 Reims Cedex 2, France
Fax +33(3)26913166; E-mail: charles.portella@univ-reims.fr
Received 26 September 1999; revised 21 February 2000
tle studied,12 despite the high potential of transformations
Abstract: 2,5-Bis(trialkylsilyl)furans and 2,6-bis(trialkylsilyl)-4H-
one can expect from such dicarbonyl compounds. We
have recently undertaken a research programme on the
synthesis of bis(acylsilanes) and their application to new
pyrans have been synthesized by cyclodehydration of 1,4- and
1,5-bis(acylsilanes) under p-toluenesulfonic acid catalysis. The
1,4-bis(acylsilanes) have been prepared from 1,2-bis(1,3-dithian-2-
yl)ethane according to the reaction sequence metallation-silylation- silylated heterocycles. The first example dealt with the
dethioketalization. The 1,5-bis(acylsilanes) have been prepared
preparation of 3,4-dihydroxybis(acylsilane) which cy-
from 1,3-bis(1,3-dithian-2-yl)propane by a similar strategy or from
clized spontaneously into (5-trimethylsilylfuran-2-
a SN reaction of 1,3-dihalopropanes with 2-trialkylsilyl-2-lithio-1,3-
yl)acetyltrimethylsilane.13
dithiane and deprotection. The method allows efficient preparation
of symmetrical as well as unsymmetrical bis(silylated) heterocy-
cles.
A general methodology to have an access to symmetrical
as well as unsymmetrical 2,5-bis(trialkylsilyl)furans and
2,6-bis(trialkylsilyl)-4H-pyrans remains
a challenge
Key words: furans, 4H-pyrans, acylsilanes, cyclizations, dithianes,
heterocycles
which could be resolved by a simple cyclodehydration of
the corresponding bis(acylsilanes). Such a strategy should
have at one’s disposal an easy access to symmetrical and
unsymmetrical 1,4- and 1,5-bis(acylsilanes). This paper is
a full account of this investigation,14 and reports on both
aspects of the methodology: the synthesis and character-
ization of the bis(acylsilanes) precursors and of the corre-
sponding bis(silylated) furans and 4H-pyrans.
Silylated furans have been a topic of continuing interest in
organic chemistry. Indeed, the peracid oxidation of substi-
tuted 2-trimethylsilylfurans to but-2-en-4-olides is the
pivotal step in the synthesis of many natural products,
namely hispanolone, prehispanolone and sphydrofuran.1
Moreover, the judicious placement of a silyl group on the
furan ring can be used to control the position of new
groups around the furan or the silane can be directly re-
placed by electrophile via an ipso-substitution.2 Only few
examples of 2,5-bis(trialkylsilyl)furans have been report-
ed. The 2,5-bis(trimethylsilyl)furan and analogs have
been studied by NMR or were involved in redox reac-
tions.3 The 1,3-bis(trimethylsilyl)-isobenzofuran4 and
naphtho[1,2-c]furan5 were used with arynes in cycloaddi-
tion. Silylated polyfurans (tetrasila[2.2]paracyclophane,6
silacalix[4]arenes7) have been studied for their coordina-
tion and photoelectron properties. All of these furans have
been prepared by silylation of dilithio derivatives with tri-
alkylsilyl chlorides in low to moderate yields. More re-
cently, an interesting electroreductive silylation of 2,5-
dibromofuran has been reported,8 but only symmetrical
2,5-bis(silyl)furans have been prepared by this method.
On the other hand, 2,6-bis(trialkylsilyl)-4H-pyrans were
unprecedented before our study. Metallation-silylation of
the corresponding 4H-pyrans was applied only to the
preparation of 2-trimethylsilyl-4H-pyrans,9a and to deriv-
atives in the related family of 2-trialkylsilyldihydropyr-
ans,9b the latter have been prepared by various cyclization
procedures.10
The more general approach to the synthesis of simple lin-
ear symmetical and unsymmetrical bis(acylsilanes) is de-
picted in Scheme 1. It consists of lithiation followed by
silylation of the bis(dithianes) 1 or 2, in a reaction using
2.4 equivalents of reagents for symmetrical compounds,
or in a two-step sequence for the unsymmetrical ones. Ox-
idative removal of the dithiane moiety led to the expected
bis(acylsilanes).
O
S
Si1
S
iv or v
Si1
S
Si1
Si1
n = 1
i, ii
S
O
3a-d
5a-d
S
H
S
n
H
S
S
n = 1 : 1
n = 2 : 2
n = 1, 2
1) i, ii
2) i, iii
O
S
Si1
S
v or vi
Si2
S
n
Si2
n
Si1
S
O
n = 1 : 5e-g
n = 2 : 6a
n = 1 : 3e-g
n = 2 : 4a
Acylsilanes, a class of compounds with interesting reac-
tivity, have been widely employed in organic synthesis.11
In contrast, the chemistry of bis(acylsilanes) have been lit-
Reagents and conditions: i) BuLi; ii) Cl-Si1; iii) Cl-Si2; iv) MeI/
CaCO3; v) Hg(ClO4)2/CaCO3; vi) I2/CaCO3
Scheme 1
Synthesis 2000, No. 6, 843–849 ISSN 0039-7881 © Thieme Stuttgart · New York

844
J.-P. Bouillon et al.
PAPER
Table 1 Synthesis of Bis(acylsilanes) 5a−g and 6a According to Scheme 1
Entry
n
Si1
Si2
Bis(dithiane)
Yield (%)
Hydrolysis
Methoda
Bis(acylsilane)
Yield (%)
1
1
1
1
1
1
1
1
2
SiMe3
–
3a
3b
3c
3d
3e
3f
78
86
47
81
88
75
91
78
iv
v
5a
5b
5c
5d
5e
5f
90
80
86
61
72
63
74
53
87
2
SiEt3
–
3
SiMe2Bu-t
Si(Pr-i)3
SiMe3
–
v
4
–
v
5
SiEt3
v
6
SiMe3
SiMe2Bu-t
Si(Pr-i)3
Si(Pr-i)3
v
7
SiMe3
3g
4a
v
5g
6a
6a
8a
8b
SiMe3
v
vi
a iv) MeI/CaCO3; v) Hg(ClO4)2/CaCO3; vi) I2/CaCO3.
1,2-Bis(1,3-dithian-2-yl)ethane 115 was obtained by treat- cept for 4g whose yield (36%) was reduced by a compet-
ment of dimethoxytetrahydrofuran with propane-1,3- ing elimination reaction, the intermediate 1,5-
dithiol and hydrogen chloride (90%), whereas the analog bis(trialkylsilyl)dithianes were obtained in excellent
216 was derived from 3,4-dihydro-2-methoxy-2H-pyran. yields (66-91%), even for hindered and/or unsymmetri-
It is worth noting that the preparation of 2 with gaseous cal derivatives. Similarly, the deprotection step gave good
hydrogen chloride (95%) gives better yield than with yields of the corresponding 1,5-bis(acylsilanes) 6b-g
BF3∑OEt2 (55%).16b Symmetrical 1,4-bis(dithianes) 3a-d (59-100%). Recent results (for example: compounds 6a,
were prepared in good yields (78-86%), even for hin- 6c and 6g) show that dethioketalization with iodine gave
dered silyl groups, except for the TBDMS derivative 3c high yield of bis(acylsilanes) without the drawback of us-
(47%) (Scheme 1, Table 1). New unsymmetrical ing heavy metal salts.
bis(dithianes) 3e-g and 4a were also synthesized in good
The 2,5-bis(trialkylsilyl)furans 8a-g were prepared by
yields (75-91%) by a two steps procedure via the trime-
cyclodehydration (Paal-Knorr type synthesis) of
thylsilylated intermediate (94% for n = 1, 85% for n = 2)
which, after purification by recrystallization from petro-
leum ether, was reacted with various trialkylsilyl chlo-
rides (Scheme 1, Table 1). The conversion of the
1,4-bis(acylsilanes) 5a-g under acid catalysis. A mixture
of 5 and a catalytic amount of p-toluenesulfonic acid (PT-
SA) was thermolysed under reduced pressure, using a
Kugelrohr apparatus to furnish silylated furans 8 (Scheme
bis(dithianes) into the corresponding bis(acylsilanes) 5a-
3, Table 3, Entries 1-7). This reaction was general and
g and 6a was performed using methyl iodide, mercuric
gave good yields (61-71%) even for hindered silyl groups
perchlorate, or iodine in the presence of calcium carbon-
such as TBDMS and TIPS. Unfortunately, this cyclodehy-
ate (Scheme 1, Table 1).14b
dration seemed to be very sensitive to substituent in posi-
1,5-Bis(acylsilanes) 6b-g were prepared according to the tion 2 of the bis(acylsilane). Indeed, the thermolysis of a-
reaction path depicted in Scheme 2, via the corresponding methyl 1,4-bis(acylsilane) failed (degradation of the start-
1,5-bis(trialkylsilyl) dithianes 4b-g derived from a SN re- ing material).14b It is worth noting that furans 8b-g have
action of 1,3-dihalopropanes with 2-trialkylsilyl-2-lithio- not been described yet in the literature.
1,3-dithiane. The results are summarized in Table 2. Ex-
1)
X
Y
R
O
O
X, Y = Cl, Br, I
S
Si1
S
R
S
S
Si2
i or ii or iii
S
S
Si1
Si2
2)
Si2
Li
S
S
Si1
Li
R
4b-g
6b-g
Reagents and conditions: i) MeI/CaCO3; ii) Hg(ClO4)2/CaCO3; iii) I2/CaCO3
Scheme 2
Synthesis 2000, No. 6, 843–849 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of Symmetrical and Unsymmetrical 2,5-Bis(trialkylsilyl)furans
845
Table 2 Synthesis of Bis(acylsilanes) 6b−g According to Scheme 2
Entry
R
Si1
Si2
Bis(dithiane) Yield (%)
Hydrolysis
Methoda
Bis(acylsilane)
Yield (%)
1
H
H
SiMe3
SiMe3
4b
4c
9116b
86
i
6b
6c
6c
6d
6e
6f
7516b
~100
97
2a
2b
3
SiMe2Bu-t
SiMe2Bu-t
ii
iii
ii
ii
ii
ii
iii
H
SiMe3
SiMePh2
SiMe2Bu-t
SiMe3
4d
4e
4f
82
66
85
36b
59
4
H
SiEt3
77
5
Me
Me
SiMe3
79
6a
6b
SiMe2Bu-t
SiMe2Bu-t
4g
6g
6g
84
90
a i) MeI/CaCO3; ii) Hg(ClO4)2/CaCO3; iii) I2/CaCO3.
b Bis(dithiane) 4g was accompanied by 2-(but-3-enyl)-2-(tert-butyldimethylsilyl)-1,3-dithiane 7 (57%).
A similar Kugelrohr treatment of 1,5-bis(acylsilanes) 6a-
g under p-toluenesulfonic acid catalysis furnished easily
the 2,6-bis(trialkysilyl)-4H-pyrans 9a-g (Scheme 3, Ta-
ble 3, Entries 8-14). In contrast to the furan series, a-me-
thyl bis(acylsilanes) 6f and 6g were effectively cyclized,
giving the corresponding 3-methyl-2,6-bis(trialkysilyl)-
4H-pyrans 9f and 9g (Table 3, Entries 13, 14).
Si2
Si1
O
n = 1
O
8a-g
Si2
n
PTSA , ∆
Si1
R
O
R
n = 2
5a-g, 6a-g
The cyclodehydration of 1,4- and 1,5-bis(acylsilanes) is
an excellent and general method to prepare 2,5-bis(tri-
alkylsilyl)furans 8a-g and 2,6-bis(trialkylsilyl)-4H-pyr-
ans 9a-g, interesting compounds for various applications.
The main interest of this method is the possible access to
Si1
O
Si2
9a-g
Scheme 3
Table 3 Synthesis of Furans 8a−g and 4H-Pyrans 9a−g According to Scheme 3
Entry
1
Bis(acylsilane)
n
1
1
1
1
1
1
1
2
2
2
2
2
2
2
R
Si1
Si2
Furan or 4H-Pyran
Yield (%)
688
67
5a
5b
5c
5d
5e
5f
H
SiMe3
SiMe3
SiEt3
8a
8b
8c
8d
8e
8f
2
H
SiEt3
3
H
SiMe2Bu-t
Si(Pr-i)3
SiMe3
SiMe2Bu-t
Si(Pr-i)3
SiEt3
71
4
H
68
5
H
67
6
H
SiMe3
SiMe2Bu-t
Si(Pr-i)3
Si(Pr-i)3
SiMe3
61
7
5g
6a
6b
6c
6d
6e
6f
H
SiMe3
8g
9a
9b
9c
9d
9e
9f
69
8
H
SiMe3
85
9
H
SiMe3
80
10
11
12
13
14
H
SiMe2Bu-t
SiMe3
SiMe2Bu-t
SiMePh2
SiMe2Bu-t
SiMe3
89
H
53
H
SiEt3
94
Me
Me
SiMe3
50
6g
SiMe2Bu-t
SiMe2Bu-t
9g
91
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846
J.-P. Bouillon et al.
PAPER
Silicagel Merck 9385 (40-63 µm) was used for flash chromatogra-
phy. All anhydrous reactions were performed under a blanket of ar-
gon. THF was distilled under argon from sodium benzophenone
ketyl. The purity of the commercially available BuLi was checked
according to Gilman.17 Trialkylsilyl chlorides were stirred with
triphenylamine and distilled before use (except TBDMS-Cl).
unsymmetrical bis(silylated) derivatives, with variable
hindered silyl groups, which would allow differentiation
of the 2,5- or 2,6-positions, for example in silyl group sub-
stitution reactions.
Melting points are uncorrected. FT-IR spectra were run on a MI-
DAS Corporation apparatus. 1H and 13C NMR spectra were record-
ed on a BRUCKER AC-250 spectrometer. TMS (d = 0.00) or
CHCl3 (d = 7.27) were used as internal standards, and CDCl3
was used as the solvent. MS data were obtained on a FISON VG
AUTOSPEC apparatus at 70 eV in the electron impact mode. Ele-
mental analyses were performed with a Perkin-Elmer CHN 2400
apparatus. All reactions were monitored by TLC (Merck F 254).
Bis(trialkylated) Symmetrical Bis(dithianes) 3a-d; General
One-Step Procedure
To a solution of 115 (18.8 mmol, 1.0 equiv) in THF (40 mL) cooled
in an ice-water bath was added a solution of BuLi in hexane
(45.1 mmol, 2.4 equiv). After stirring for 30 min at 0 °C, trialkyl-
silyl chloride (45.1 mmol, 2.4 equiv) was added dropwise. The mix-
ture was then stirred for 1 h at 0 °C. The same procedure was repeat-
Table 4 Spectroscopic Data of Bis(dithianes) 3a,d,f,g and 4c,d,f
Prod- Rf (solvent)b
ucta
Mpc
(°C)
IR (KBr)
MS
m/z
1H NMR (CDCl3)
d, J (Hz)
13C NMR (CDCl3)
d
n (cm-1)
3a
0.35
petroleum ether/
Et2O (98:2)
152-154 2946, 1458,
410 (M+),
231, 191,
179
0.23 (s, 18 H), 1.8-2.1 (m, 4 H),
-2.5 [Si(CH3)3], 23.2 (CH2),
1422, 1238
2.4-2.5 (m, 8 H), 3.14 (td, 4 H, J 25.2 (CH2) , 35.4 (CH2), 39.2
= 14.5, 2.3)
(C4)
3d
0.51
petroleum ether/
Et2O (99:1)
112-114 2948, 2865,
578 (M+),
535, 157,
115
1.27 (d, 36 H, J = 7.3), 1.51 (sept, 12.4 (SiCH), 20.1 (CH3),
6 H, J = 7.3), 1.8-2.1 (m, 4 H), 24.4 (CH2), 25.4 (CH2), 39.7
2.48 (ddd, 4 H, J = 14.1, 3.8, 3.5), (CH2), 41.4 (C4)
2.73 (s, 4 H), 3.15 (ddd, 4 H, J =
13.2, 13.0, 2.7)
1460, 1271
3f
0.30
petroleum ether/
Et2O (99:1)
112-114 2936, 2855,
452 (M+),
337, 221,
179
0.24 (s, 15 H), 1.08 (s, 9 H), 1.8- -5.3 [Si(CH3)2], -2.4
1422, 1248
2.1 (m, 4 H), 2.4-2.5 (m, 4 H),
2.53 (m, 4 H), 3.1-3.2 (m, 4 H)
[Si(CH3)3], 19.8 (C4), 23.3
(CH2), 23.5 (CH2) , 25.0
(CH2), 25.1 (CH2), 28.4
(CH3), 35.8 (CH2), 36.7
(CH2), 39.3 (C4), 41.2 (C4)
3g
0.37
petroleum ether/
Et2O (99:1)
106-107 2948, 2865,
494 (M+),
263, 191,
157
0.25 (s, 9 H), 1.27 (d, 18 H, J =
7.3), 1.49 (sept, 3 H, J = 7.3),
1.9-2.1 (m, 4 H), 2.3-2.7 (m, 8
-2.4 [Si(CH3)3], 12.4
(SiCH), 20.2 (CH3), 23.6
(CH2), 24.6 (CH2), 24.8
1458, 1244
H), 3.13 (ddd, 2 H, J = 13.9, 12.4, (CH2), 25.1 (CH2), 36.2
2.7), 3.18 (ddd, 2 H, J = 13.7,
12.4, 2.7)
(CH2), 38.6 (CH2), 39.3 (C4),
41.7 (C4)
4c
Petroleum etherd
Petroleum etherd
121-123 2957, 2853,
508 (M+),
261, 203,
145
0.24 (s, 12 H), 1.06 (s, 18 H),
1.8-2.1 (m, 6 H), 2.3-2.4 (m,
8 H), 3.05 (ddd, 4 H, J = 13.5,
13.1, 2.7)
-5.3 [Si(CH3)2], 19.9 (C4),
23.3 (CH2), 25.0 (CH2), 26.9
(CH2), 28.3 (CH3), 38.1
(CH2), 41.0 (C4)
1419, 1253
4d
142-144 3069, 2951,
548 (M+),
351, 197,
145
0.12 (s, 9 H), 0.81 (s, 3 H), 1.5-1.7 -3.8 (SiCH3), -2.7
(m, 2 H), 1.8-2.1 (m, 6 H), 2.2-2.3 [Si(CH3)3], 23.2 (CH2), 23.8
(m, 2 H), 2.3-2.5 (m, 4 H), 2.84
1428, 1250
(CH2), 24.7 (CH2), 25.0
(ddd, 2 H, J 13.5, 13.2, 2.7), 3.03 (CH2), 25.7 (CH2), 36.7 (C4),
(ddd, 2 H, J 12.8, 12.4, 3.4), 7.3- 37.6 (CH2), 38.4 (CH2), 39.1
7.5 (m, 6 H), 7.84 (d, 4 H, J 6.5)
(C4), 127.5 (CH), 129.5
(CH), 134.1 (C4), 135.8 (CH)
4f
0.38
petroleum ether/
EtOAc (99:1)
124-127 2948, 2897,
438 (M+),
205, 191,
159
0.22 (s, 9 H), 0.25 (s, 9 H), 1.30
-2.6 [Si(CH3)3], -0.2
1424, 1273
(d, 3 H, J 6.9), 1.8-2.2 (m, 6 H), [Si(CH3)3], 18.3 (CH3), 23.3
2.3-2.6 (m, 7 H), 2.9-3.2 (m, 4 H) (CH2), 23.5 (CH2), 23.6
(CH2), 24.7 (CH2), 25.2
(CH2), 33.0 (CH2), 37.4
(CH2), 38.8 (C4), 40.6 (CH),
45.0 (C4)
a Satisfactory microanalyses for all crystallized compounds: C 0.4; H 0.4.
b Solvents used for TLC and chromatographic separation.
c White crystals.
d Recrystallization
Synthesis 2000, No. 6, 843–849 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of Symmetrical and Unsymmetrical 2,5-Bis(trialkylsilyl)furans
847
ed with BuLi (11.3 mmol, 0.6 equiv) and trialkylsilyl chloride (11.3
mmol, 0.6 equiv). After another 1 h at 0 °C, the reaction was
quenched with H2O (100 mL). The crude mixture was extracted
with Et2O (4 × 50 mL). The combined organic phases were dried
(MgSO4) and concentrated in vacuo. The residue was chromato-
graphed on silica gel using mixture of petroleum ether/Et2O (Tables
1 and 4).
1-(1,3-Dithian-2-yl)-3-(2-trimethylsilyl-1,3-dithian-2-yl)pro-
pane
The same procedure of monoalkylation with trimethylsilyl chloride
applied to 2 (6.7 g, 24.0 mmol) gave after two successive recrystal-
lizations from petroleum ether the corresponding bis(silylated)
compound (1.2 g, 11%)16b and the mono trimethylsilylated
bis(dithiane) intermediate (7.2 g, 85%) as a yellow oil.
Mono Trimethylsilylated Intermediates for Two-Step Reac-
tions; 1-(1,3-Dithian-2-yl)-2-(2-trimethylsilyl-1,3-dithian-2-
yl)ethane; Typical Procedure
Mono Trimethylsilylated Bis(dithiane) Intermediate Corre-
sponding to n = 2, Si1 = SiMe3 (cf. Scheme 1)
Rf 0.26 (petroleum ether/Et2O, 99:1).
Monosilylation of 1 (5.0 g, 18.8 mmol) with BuLi in hexane (10.1
mL, 19.7 mmol) and trimethylsilyl chloride (2.5 ml, 19.7 mmol), by
a procedure similar to that reported for 3a–d, gave after recrystalli-
zation from petroleum ether the mono trimethylsilylated
bis(dithiane) intermediate (5.9 g, 94%) as a white solid; mp 91-
92 °C; Rf 0.33 (petroleum ether/EtOAc, 96:4).
1H NMR: d = 0.20 (s, 9 H), 1.8-2.2 (m, 6 H), 2.4-2.5 (m, 4 H), 2.8-
2.9 (m, 4 H), 3.08 (ddd, J = 13.6, 13.1, 2.7 Hz, 2 H), 4.08 (dd,
J = 6.9, 6.5 Hz, 1 H).
1H NMR: d = 0.21 (s, 9 H), 1.6-2.0 (m, 6 H), 2.0-2.3 (m, 4 H), 2.4-
2.5 (m, 2 H), 2.8-2.9 (m, 4 H), 3.04 (m, 2 H), 4.10 (dd, J = 6.9, 6.5
Hz, 1 H).
13C NMR: d = -2.7 [Si(CH3)3], 23.3 (CH2), 24.6 (CH2), 25.0 (CH2),
25.9 (CH2), 30.3 (CH2), 35.6 (CH2), 36.6 (CH2), 38.4 (C4), 47.1
(CH).
IR (film): n = 2897, 2847, 1422, 1248, 911 cm-1.
MS: m/z = 352 (M+), 279, 179, 145, 113.
13C NMR: d = -2.7 [Si(CH3)3], 23.1 (CH2), 25.0 (CH2), 25.9 (CH2),
30.3 (CH2), 33.5 (CH2), 33.8 (CH2), 38.2 (C4), 47.7 (CH).
Anal. calcd for C14H28SiS4: C 47.68, H 8.00; found: C 47.89, H
8.32.
IR (KBr):n = 2903, 2857, 1453, 1410, 1250 cm-1.
MS: m/z = 338 (M+), 265, 206, 159, 132, 107.
Unsymmetrical Bis(dithianes) 3e-g and 4a; General Two-Step
Procedure
Silylation of mono trimethylsilylated bis(dithiane) intermediate
(7.4 mmol, 1.0 equiv) with BuLi in hexane (8.2 mmol, 1.1 equiv)
and trialkylsilyl chloride (8.2 mmol, 1.1 equiv), by a procedure sim-
ilar to that reported for 3a-d, gave after chromatography on silica
Anal. calcd for C13H26SiS4: C 46.10, H 7.74; found: C 46.28, H
8.04.
Table 5 Spectroscopic Data of Bis(acylsilanes) 5a,d,f,g and 6c,d,f
Prod-
ucta,b
Rf (solvent)c
IR (film)
MS
m/z
1H NMR (CDCl3)
d, J (Hz)
13C NMR (CDCl3)
d
n (cm−1)
5a
5d
5f
0.49
petroleum ether/
EtOAc (96:4)
2961, 1644,
1250, 843
230 (M+),
220, 205,
147
0.18 (s, 18 H), 2.80 (s, 4 H)
-3.3 [Si(CH3)3], 40.0 (CH2), 245.3
(CO)
0.49
petroleum ether/
EtOAc (99:1)
2946, 2869,
1634, 1387
398 (M+),
355, 157,
115
1.11 (d, 36 H, J = 7.2), 1.29 (sept, 6 H, 10.7 (SiCH), 18.5 (CH3), 43.0
J = 7.2), 2.84 (s, 4 H)
(CH2), 244.2 (CO)
0.35
petroleum ether/
EtOAc (98:2)
2957, 2861,
1642, 1250
272 (M+),
215, 147,
115
0.21 (s, 6 H), 0.23 (s, 9 H), 0.94 (s,
9 H), 2.84 (m, 4 H)
-7.1 [Si(CH3)2], -3.3 [Si(CH3)3],
16.4 (C4), 26.3 (CH3), 40.0 (CH2),
42.3 (CH2), 244.6 (CO), 245.5 (CO)
5g
6c
6d
0.55
petroleum ether/
EtOAc (96:4)
2946, 2869,
1638, 1250
314 (M+),
299, 157,
115
0.23 (s, 9 H), 1.11 (d, 18 H, J 6.9), 1.28 -3.3 [Si(CH3)3], 10.6 (SiCH), 18.4
(sept, 3 H, J = 6.9), 2.84 (m, 4 H)
(CH3), 39.5 (CH2), 43.6 (CH2),
244.1 (CO), 245.4 (CO)
0.35
petroleum ether/
EtOAc (97:3)
2930, 2859,
1640, 1250
328 (M+),
189, 159,
147
0.16 (s, 12 H), 0.91 (s, 18 H), 1.72
(quint, 2 H, J = 6.9), 2.59 (t, 4 H, J =
6.9)
-7.0 (SiMe2), 14.4 (CH2), 16.5 (C4),
26.4 (CH3), 49.3 (CH2), 247.1 (CO)
0.32
petroleum ether/
EtOAc (96:4)
3052, 2957,
1642, 1250
368 (M+),
209, 197,
149
0.15 (s, 9 H), 0.77 (s, 3 H), 1.73 (quint, -5.5 (SiCH3), -3.3 [Si(CH3)3], 14.8
2 H, J = 6.9), 2.52 (t, 2 H, J = 6.9), 2.67 (CH2), 47.3 (CH2), 48.7 (CH2),
(t, 2 H, J = 6.9), 7.35-7.50 (m, 6 H),
7.55-7.65 (m, 4 H)
128.2 (CH), 130.1 (CH), 132.6 (C4),
134.9 (CH), 244.0 (CO), 247.6 (CO)
6f
0.33
petroleum ether/
ETOAc (96:4)
2961, 2903,
1642, 1250
258 (M+),
185, 147,
131
0.20 (s, 9 H), 0.22 (s, 9 H), 0.97 (d, 3H, -3.3 [Si(CH3)3], -2.7 [Si(CH3)3],
J = 6.9), 1.4-1.6 (m, 1 H), 1.90 (dddd, 14.4 (CH3), 23.0 (CH2), 45.5 (CH2),
1 H, J = 14.5, 7.6, 7.3, 6.9), 2.54 (m,
2 H), 2.89 (hex, 1 H, J = 6.9)
49.4 (CH), 247.4 (CO), 250.3 (CO)
a Oil.
b Satisfactory microanalyses obtained.
c Solvents used for TLC and chromatographic separation.
Synthesis 2000, No. 6, 843–849 ISSN 0039-7881 © Thieme Stuttgart · New York

848
J.-P. Bouillon et al.
PAPER
Table 6 Spectroscopic Data of Furans 8b−g and 4H-Pyrans 9a−g
Prod- Thermolysis (°C)
IR (film)
MS
m/z
1H NMR (CDCl3)
d, J (Hz)
13C NMR (CDCl3)
d
uctsa,b
n (cm−1)
8b
8c
8d
8e
8f
80-90
83-85
120-135
65-70
75-85
80-90
80-90
75-85
85-90
80-90
2955, 2878,
1537, 1460
296 (M+),
267, 189,
115
0.77 (q, 12 H, J = 8.0), 1.01 (t, 18H, J = 3.4 (SiCH2), 7.3 (CH3), 119.9 (CH),
7.6), 6.64 (s, 2 H) 162.6 (C4)
2955, 2859,
1539, 1472
296 (M+),
239, 167,
147
0.23 (s, 12 H), 0.92 (s, 18 H), 6.63 (s, 2 H) -6.3 [Si(CH3)2], 16.8 (C4), 26.3
(CH3), 120.1 (CH), 163.1 (C4)
2946, 2867,
1537, 1464
380 (M+),
337, 295,
119
1.09 (d, 36 H, J = 6.9), 1.31 (sept, 6 H, J = 11.2 (SiCH), 18.6 (CH3), 120.9 (CH),
6.9), 6.68 (s, 2 H)
160.9 (C4)
2957, 2878,
1539, 1460
254 (M+),
225, 147,
130
0.27 (s, 9 H), 0.77 (q, 6 H, J = 8.0), 1.00 -1.6 [Si(CH3)3], 3.4 (SiCH2), 7.3
(t, 9 H, J = 8.0), 6.62 (m, 2 H)
(CH3), 118.9 (CH), 120.0 (CH),
162.7 (C4), 164.5 (C4)
2957, 2859,
1539, 1472
254 (M+),
239, 197,
147
0.24 (s, 6 H), 0.27 (s, 9 H), 0.93 (s, 9 H), -6.2 [Si(CH3)2], -1.6 [Si(CH3)3],
6.62 (m, 2 H)
16.9 (C4), 26.3 (CH3), 118.9 (CH),
120.3 (CH), 163.0 (C4), 164.6 (C4)
8g
9a
9b
9c
9d
2946, 2869,
1539, 1464
296 (M+),
253, 211,
115
0.26 (s, 9 H), 1.10 (d, 18 H, J = 6.9), 1.27 -1.6 [Si(CH3)3], 11.2 (SiCH), 18.6
(sept, 3 H, J = 6.9), 6.62 (d, 1 H, J = 3.1), (CH3), 118.7 (CH), 120.9 (CH),
6.66 (d, 1 H, J = 3.1)
161.3 (C4), 164.2 (C4)
2942, 2865,
1609, 1246
310 (M+),
237, 153
0.09 (s, 9 H), 1.0-1.2 (m, 21 H), 2.66 (dd, -2.7 [Si(CH3)3], 10.5 (SiCH), 18.6
2 H, J = 3.4, 3.1), 5.00 (dd, 2 H, J = 3.4, (CH3), 19.2 (CH2), 109.3 (CH), 111.7
3.1)
(CH), 154.0 (C4), 157.5 (C4)
2959, 2899,
1608, 1249
226 (M+),
168, 153,
147
0.10 (s, 18 H), 2.61 (t, 2 H, J = 3.3), 5.00 -2.8 [Si(CH3)3], 19.3 (CH2), 109.4
(t, 2 H, J = 3.3) (CH), 157.9 (C4)
2953, 2930,
1607,1248
310 (M+),
195, 115
0.05 (s, 12 H), 0.93 (s, 18 H), 2.65 (t, 2 H, -7.0 [Si(CH3)2], 16.4 (C4), 19.3
J = 3.4), 4.98 (t, 2 H, J = 3.4)
(CH2), 26.6 (CH3), 110.9 (CH), 156.1
(C4)
3069, 2959,
1609, 1248
350 (M+),
277, 153
0.08 (s, 9 H), 0.68 (s, 3 H), 2.67 (t, 2H,
J = 3.1), 5.00-5.15 (m, 2 H), 7.3-7.4
(m, 6 H), 7.6-7.7 (m, 4 H)
-5.1 (SiCH3), -2.8 [Si(CH3)3], 19.5
(CH2), 109.5 (CH), 113.7 (CH),
127.7 (CH), 129.4 (CH), C4 (not ob-
served), 135.1 (CH), 154.7 (C4),
157.9 (C4)
9e
85-95
2953, 2928,
1607, 1246
310 (M+),
195, 115
0.04 (s, 6 H), 0.60 (q, 6 H, J = 8.0), 0.92 -7.1 [Si(CH3)2], 2.3 (SiCH2), 7.3
(s, 9 H), 0.96 (t, 9 H, J = 8.0), 2.63 (m,
2 H), 4.9-5.0 (m, 2 H)
(CH3), 16.4 (C4), 19.2 (CH2), 26.6
(CH3), 110.7 (CH), 110.9 (CH),
155.4 (C4), 156.2 (C4)
9f
75-85
85-95
2959, 2924,
1620, 1248
240 (M+),
182, 167,
147
0.11 (s, 9 H), 0.20 (s, 9 H), 1.61 (s, 3 H), -2.6 [Si(CH3)3], -0.7 [Si(CH3)3],
2.54 (d, 2 H, J = 2.7), 5.05 (dd, 1 H, J = 19.2 (CH3), 25.9 (CH2), 108.7 (CH),
3.4, 3.1)
118.1 (C4), 149.3 (C4), 156.8 (C4)
9g
2928, 2857,
1617, 1250
324 (M+),
267, 167,
147
0.05 (s, 6 H), 0.17 (s, 6 H), 0.92 (s, 9 H), -6.9 [Si(CH3)2], -4.2 [Si(CH3)2],
0.93 (s, 9 H), 1.59 (s, 3 H), 2.57 (dd, 2 H, 16.5 (C4), 17.9 (C4), 20.2 (CH3), 26.2
J = 3.4, 1.1), 5.02 (t, 1 H, J = 3.4)
(CH2), 26.7 (CH3), 26.8 (CH3), 110.2
(CH), 119.1 (C4), 147.9 (C4), 154.9
(C4)
a Oil.
b Satisfactory microanalyses obtained.
gel using a mixture of petroleum ether/Et2O the unsymmetrical
bis(dithianes) 3e-g and 4a (Tables 1 and 4).
Dethioketalization with Mercury(II) Perchlorate; General Pro-
cedure
To a solution of bis(dithiane) 3 or 4 (5.0 mmol, 1.0 equiv) in a
mixture THF/H2O (80:20, 30 mL) were added CaCO3 (30.5 mmol,
6.1 equiv), Hg(ClO4)2 (30.0 mmol, 6.0 equiv). The mixture was
Dethioketalization with Methyl Iodide; General Procedure
The dethioketalization of 3 and 4 with MeI was carried out accord-
ing to the procedure reported by us in Ref. 12 (Tables 1, 2, 5).
Synthesis 2000, No. 6, 843–849 ISSN 0039-7881 © Thieme Stuttgart · New York

PAPER
Synthesis of Symmetrical and Unsymmetrical 2,5-Bis(trialkylsilyl)furans
849
stirred at r.t. until total conversion (overnight), and was then parti-
tioned between CH2Cl2 (150 mL) and brine (100 mL). After filtra-
tion through Celite, the filtrate was extracted with CH2Cl2 (5 × 50
mL). The combined organic extracts were dried (MgSO4), filtered
and concentrated in vacuo. The residue was chromatographed over
silica gel using petroleum ether/EtOAc as eluent (Tables 1, 2, 5).
References
(1) Wong, H. N. C. Eur. J. Org. Chem. 1999, 1757.
(2) Keay, B. A. Chem. Soc. Rev. 1999, 28, 209.
(3) (a) Lukevics, E.; Voronkov, M. G. Khim. Geterotsikl. Soedin.
1965, 1, 19; Chem. Abstr. 1965, 63, 2994.
(b) Pinkerton, F. H.; Thames, S. F. J. Heterocycl. Chem. 1970,
7, 747.
Dethioketalization with Iodine; General Procedure
(c) Bock, H.; Roth, B. Phosphorus and Sulfur 1983, 14, 211.
(d) Carman, C. S.; Koser, G. F. J. Org. Chem. 1983, 48, 2534.
(e) Lukevics, E.; Erchak, N. P.; Matorykina, V. F.; Mazeika,
I. J. Gen. Chem. USSR (Engl. Transl.) 1983, 53, 959; Chem.
Abstr. 1984, 101, 171334.
To a solution of the bis(dithiane) 3 or 4 (7.7 mmol, 1.0 equiv) in
THF/H2O (80:20, 40 mL), at r.t., were added CaCO3 (92.4 mmol,
12.0 equiv) and I2 (69.3 mmol, 9.0 equiv). The mixture was stirred
at the same temperature until total conversion (overnight), then par-
titioned between Et2O (100 mL) and satd aq Na2S2O3 solution (60
mL). After stirring for 10 min, the crude was filtered over Celite and
extracted with Et2O (5 × 50 mL). The organic phase was dried
(MgSO4), filtered and concentrated in vacuo. The residue was chro-
matographed over silica gel using petroleum ether/EtOAc as eluent
(Tables 1, 2, 5).
(4) Crump, S. L.; Netka, J.; Rickborn, B. J. Org. Chem. 1985, 50,
2746.
(5) Pollart, D. J.; Rickborn, B. J. Org. Chem. 1986, 51, 3155.
(6) Gleiter, R.; Schäfer, W.; Krennrich, G.; Sakurai, H. J. Am.
Chem. Soc. 1988, 110, 4117.
(7) König, B.; Rödel, M.; Bubenitschek, P.; Jones, P. G.;
Thondorf, I. J. Org. Chem. 1995, 60, 7406.
(8) Moreau, C.; Serein-Spirau, F.; Bordeau, M.; Biran, C. J.
Organomet. Chem. 1998, 570, 147.
Bis(dithianes) 4b,c,f,g; General Procedure
The bis(dithianes) were prepared according to the procedure report-
ed by us in Ref. 12 (Tables 2 and 4).
(9) (a) Schlosser, M.; Schneider, P. Angew. Chem. Int. Ed. Engl.
1979, 18, 489.
(b) Gevorgyan, V.; Borisova, L.; Lukevics, E. J. Organomet.
Chem. 1992, 441, 381.
(10) (a) Tsai, Y. -M.; Nieh, H. -C.; Cherng, C. -D. J. Org. Chem.
1992, 57, 7010.
Unsymmetrical Bis(dithianes) 4d-e; General Procedure
(Scheme 2)
To a solution of the 2-trialkylsilyl-1,3-dithiane (10.0 mmol,
1.1 equiv) in THF (30 mL) cooled to -25 °C was added dropwise a
solution of BuLi hexane (10.0 mmol, 1.1 equiv) over a period of 5
min. After stirring for 2.5 h at -25 °C, a solution of 1-chloro-3-io-
dopropane (9.1 mmol, 1.0 equiv) in THF (10 mL) was added at
0 °C. The mixture was stirred for a further 2 h at 0 °C, and then a
solution of another 2-trialkylsilyl-2-lithio-1,3-dithiane (10.9 mmol,
1.2 equiv, prepared by the same procedure) was added dropwise
over a period of 5 min. After stirring overnight at 0 °C, the reaction
was quenched by the addition of satd aq NH4Cl solution (50 mL).
The crude mixture was extracted with Et2O (3 × 50 mL). The com-
bined organic phases were dried (MgSO4), filtered and concentrated
in vacuo. The residue was recrystallized from petroleum ether (Ta-
bles 2 and 4). The bis(dithiane) 4g was accompanied by 2-(but-3-
enyl)-2-(tert-butyldimethylsilyl)-1,3-dithiane 7.
(b) Tsai, Y. -M.; Cherng, C. -D.; Nieh, H. -C.; Sieh, J. -A.
Tetrahedron 1999, 55, 14587.
(c) Heathcock, C. H.; Norman, M. H.; Dickman, D. A. J. Org.
Chem. 1990, 55, 798.
(11) For recent reviews:
(a) Cirillo, P. F.; Panek, J. S. Org. Prep. Proc. Int. 1992, 24,
555.
(b) Nájera, C.; Yus, M. Org. Prep. Proc. Int. 1995, 27, 385.
(c) Bonini, B. F.; Franchini, M. C.; Fochi, M.; Mazzanti, G.;
Ricci, A. Gazz. Chim. Ital. 1997, 127, 619.
(12) Bouillon, J. -P.; Portella, C. Eur. J. Org. Chem. 1999, 1571,
and references therein.
(13) Bouillon, J. -P.; Portella, C. Tetrahedron Lett. 1997, 38, 6595.
(14) Preliminary reports:
Compound 7
(a) Saleur, D.; Bouillon, J. -P.; Portella, C. Tetrahedron Lett.
1999, 40, 1885.
(b) Saleur, D.; Bouillon, J. -P.; Portella, C. Tetrahedron Lett.
2000, 41, 321.
Yield: 57%; oil.
1H NMR: d = 0.22 (s, 6 H), 1.04 (s, 9 H), 1.8-2.1 (m, 2 H), 2.3-2.5
(m, 6 H), 3.06 (ddd, J = 13.5, 13.2, 2.7 Hz, 2 H), 4.9-5.1 (m, 2 H),
5.8-6.0 (m, 1 H).
13C NMR: d = -5.3 [Si(CH3)2], 19.7 (C4), 23.4 (CH2), 24.9 (CH2),
28.2 (CH3), 32.4 (CH2), 36.9 (CH2), 40.7 (C4), 114.6 (CH2), 138.3
(CH).
(15) (a) Seebach, D.; Jones, N. R.; Corey, E. J. J. Org. Chem. 1968,
33, 300.
(b) Sudweeks, W. B.; Broadbent, H. S. J. Org. Chem. 1975,
40, 1131.
IR (film): n = 3082, 2937, 2853, 1637, 1469, 1253 cm-1.
MS: m/z = 289 (M+), 273, 247, 189, 173.
(16) (a) Corey, E. J.; Seebach, D. Angew. Chem., Int. Ed. Engl.
1965, 4, 1077.
(b) Chuang, T. -H.; Fang, J. -M.; Jiaang, W. -T.; Tsai, Y. -M.
J. Org. Chem. 1996, 61, 1794.
HRMS: m/z calcd for C14H28SiS2 288.1402; found 288.1420.
(17) Gilman, H.; Haubein, A. H. J. Am. Chem. Soc. 1944, 66, 1515.
Furans 8a-g and 4H-Pyrans 9a-g; General Procedure
A mixture of 1,4- or 1,5-bis(acylsilane) 5 or 6 (5.0 mmol, 1.0 eq.)
and p-toluenesulfonic acid (0.5 mmol, 0.1 equiv) was thermolysed
under reduced pressure (0.05 mbar), using a Büchi Kugelrohr appa-
ratus, to give 2,5-bis(trialkylsilyl)furans 8a-g or 2,6-bis(trialkylsi-
lyl)-4H-pyrans 9a-g, respectively (Tables 3 and 6).
Article Identifier:
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Synthesis 2000, No. 6, 843–849 ISSN 0039-7881 © Thieme Stuttgart · New York