Diastereoselective Intramolecular Silylformylation of ω-Silylacetylenes

Full text of DOI:10.1021/jo991129y

J . Org. Chem. 1999, 64, 9711-9714
9711
Notes
Dia ster eoselective In tr a m olecu la r
Sch em e 1
Silylfor m yla tion of ω-Silyla cetylen es
Laura Antonella Aronica, Anna Maria Caporusso, and
Piero Salvadori*
Dipartimento di Chimica e Chimica Industriale, Centro di
Studio del CNR per le Macromolecole Stereordinate ed
Otticamente Attive, Via Risorgimento 35, 56126 Pisa, Italy
Howard Alper
Sch em e 2
Department of Chemistry, University of Ottawa,
1
0 Marie Curie, Ottawa, K1N 6N5 Canada
Received J uly 15, 1999
The silylformylation reaction of unsaturated com-
pounds consists of the simultaneous introduction of a
trialkylsilyl group and a formyl moiety into a carbon-
carbon multiple bond in the presence of a rhodium
catalyst. This reaction has been intensively studied in
Ta ble 1. Syn th esis of ω-Silyla cetylen es 1a -ca
1
Si:Brb
Mg:Brc
yieldd (%)
recent years since it represents an extension of the well-
entry
R
t (h)
1
2
known hydroformylation process in which the H
2
mol-
1
2
3
4
5
H
H
CH3
CH3
tBu
3
24
3
72
3
1
1
1
3
1
10
2
2
2
2
a
a
b
b
c
40
38
30
8
ecule is replaced by a hydrosilane. Enol silyl ethers are
formed as the major products when alkenes are used in
3
the silylformylation reaction (Scheme 1a). On the other
37
hand, reactions involving an alkyne, carbon monoxide
and a hydrosilane give carbon-centered silanes exclu-
a
Reactions were carried out in THF on a 10 mmol scale of
b
4
alkyne, at 40 °C; see the Experimental Section. Chlorosilane:
sively (Scheme 1b).
c
bromide (mmol/mmol) ratio. Magnesium:bromide (mmol/mmol)
In sharp contrast to the hydroformylation reaction,
which often requires high CO/H pressure and generates
2
ratio. d Yields of purified products.
a mixture of saturated and unsaturated aldehydes, the
silylformylation of acetylenes occurs under mild condi-
tions and affords â-silylenaldehydes (Scheme 1b) in high
yields. The regio- and stereochemical control of this
process seems to be governed by the steric hindrance of
the substituents: the formyl moiety is always introduced
Reverse regioselectivity is observed if terminal alkyn-
ylsilanes are reacted with CO (Scheme 1c).
7
In contrast with the intermolecular reaction, in the
intramolecular process it is not the internal sp carbon
which is selectively formylated, but the terminal one,
since the ring closure takes place according to the exo-
5
at the sp carbon bearing the bulkier group. Thus, in the
8
dig Baldwin rule. Here we report new results on the
silylformylation of terminal acetylenes, (Z)-3-silyl-2-
rhodium-catalyzed intramolecular silylformylation of
substituted ω-silylacetylenes, which are building blocks
of considerable potential in organic synthesis.
6
alkenals are obtained (Scheme 1b).
(1) (a) Chatani, N.; Murai, S. Synlett 1996, 414. (b) Ojima, I.; Close,
N.; Donovan, R. J .; Ingallina, P. Organometallics 1990, 9, 3127. (c)
Eguchi, M.; Zeng, Q.; Korda, A.; Ojima, I. Tetrahedron Lett. 1993, 34,
Resu lts a n d Discu ssion
9
1
1
15. (d) Ojima, I.; Tzamarioudaki, M.; Tsai, C. Y. J . Am. Chem. Soc.
994, 116, 3643. (e) Ojima, I.; Kass, D. F.; Zhu, J . W. Organometallics
994, 15, 5191. (f) Ojima, I.; McCullagh, J . U.; Shay, W. R. J .
3
For this study, both linear and C -branched 6-(meth-
ylphenylsilyl)-1-hexynes 1 were synthesized starting from
the corresponding bromides 2, according to the procedure
reported by Alper and co-workers (Scheme 2). The yields
are given in Table 1.
Organomet. Chem. 1996, 521, 421. (g) Ojima, I.; Li, Z. Y.; Donovan, R.
J .; Ingallina, P. Inorg. Chim. Acta 1998, 270, 279. (h) Ojima, I.; Zhu,
J . W.; Vidal. E. S.; Kass, D. F. J . Am. Chem. Soc. 1998, 120, 6690.
9
(
(
2) Ungvary, F. Coord. Chem. Rev. 1997, 160, 129.
3) (a) Seki, Y.; Hidaka, A.; Murai, S.; Sonoda, N. Angew. Chem.,
Int. Ed. Engl. 1977, 16, 174. (b) Seki, Y.; Hidaka, A.; Murai, S.; Sonoda,
N. Angew. Chem., Int. Ed. Engl. 1977, 16, 881. (c) Seki, Y.; Kawamoto,
K.; Chatani, N.; Hidaka,; Sonoda, N.; Kawasaki, Y.; Murai, S. J .
Organomet. Chem. 1991, 403, 73. (d) Chatani, N.; Ikeda, S.; Murai, S.
J . Am. Chem. Soc. 1992, 114, 9710.
In a typical run, a mixture of the alkyne (10 mmol)
and MePhSi(H)Cl in THF was slowly added to a suspen-
sion of magnesium turnings in THF, previously activated
with 1,2-dibromoethane, and the reaction mixture was
(
4) (a) Matsuda, I.; Ogiso, A.; Sato, S.; Izumi,Y. J . Am. Chem. Soc.
989, 111, 2332. (b) Zhou, J .; Alper, H. Organometallics 1994, 13, 1586.
c) Doyle, M. P.; Shanklin, M. S. Organometallics 1994, 13, 1081.
5) Matsuda, I.; Fukuta, Y.; Tsuchihashi, T.; Nagashima, H.; Itoh,
K. Organometallics 1997, 16, 4327.
6) (a) Ojima, I.; Ingallina, P.; Donovan, R. J .; Clos, N. Organome-
1
(
(7) (a) Monteil, F.; Matsuda, I.; Alper, H. J . Am. Chem. Soc. 1995,
117, 4419. (b) Ojima, I.; Vidal, E.; Tzamarioudaki, M.; Matsuda, I. J .
Am. Chem. Soc. 1995, 117, 6797.
(
(
(8) Baldwin,J . E. J . Chem. Soc., Chem. Commun. 1976, 734.
(9) ω-Bromoacetylenes 2 were obtained from the corresponding
tallics 1991, 10, 38. (b) Ojima, I.; Donovan, R. J .; Eguchi, M.; Shay,
W. R.; Ingallina, P.; Korda, A.; Zeng, Q. Tetrahedron 1993, 49, 5444.
1
0
alkynyl alcohols via the quantitative formation of p-toluenesulfonates.
1
0.1021/jo991129y CCC: $18.00 © 1999 American Chemical Society
Published on Web 12/02/1999

9
712 J . Org. Chem., Vol. 64, No. 26, 1999
Notes
Sch em e 3
Sch em e 5
Ta ble 2. In tr a m olecu la r Silylfor m yla tion of
+
- a
ω-Silyla cetylen es P r om oted by Rh (C7H8)BP h 4
ratio of
diastereomers
(cis:trans)
Sch em e 4a
PCO
(atm)
yieldb
(%)
c
entry
R
t (h)
6
1
2
3
4
CH3
tBu
tBu
tBu
20
20
20
50
24
24
48
24
b
c
c
c
73
20
58
70
50:50
100:0
100:0
100:0
_
+
a
Reactions were performed in a 40 mL stainless steel autoclave,
with 1 mmol of reagent and 0.01 mmol of the catalyst (1%), at 40
C. Isolated yields. c Calculated from H NMR peaks of the
b
1
°
a
Reactions perfomed in a 40 mL stainless steel autoclave, with
aldehydic protons.
1
mmol of reagent and 0.01 mmol of the catalyst (1%), at 40 °C
for 24 h, under 20 atm of CO.
the pure aldehyde 6a was obtained in good yields (53-
6
1%). The reaction is completely regioselective: exo-dig
stirred at 40 °C for the times indicated in Table 1. The
reaction was not affected either by a high chlorosilane:
bromide ratio (Table 1, entry 4) or by long reaction times
ring closure with (Z)-double bond formation, affording the
six-membered formyl derivative.
13
+
-
The air-stable zwitterionic complex Rh (C
was used in subsequent reactions involving 1b and 1c
Scheme 5, Table 2). As is evident from the data in Table
, the presence of a C -substituent on the ω-silylacety-
7 8 4
H )BPh
(Table 1, entries 2-4). The presence of a large excess of
Mg turnings (Table 1, entry 1 vs entry 2) did not increase
the yield of the ω-silylalkynes. Fair yields (30-40%) of 1
were obtained, and the reaction is probably dependent
on the presence of two acidic protons in 2, the acetylenic
and the propargyl ones. It is well-known that Grignard
reagents can easily undergo metal-proton exchange.
Moreover, the reaction temperature must be strictly
maintained at 40 °C to avoid carbometalation side
reactions.11 Indeed, when 6-bromo-1-hexyne (2a ) and
chloromethylphenylsilane were reacted with activated
magnesium at higher temperature (60-70 °C), [(meth-
ylphenylsilyl)methylene]cyclopentane (3) was formed in
(
2
3
lenic precursor did not affect the regioselectivity of the
process, with the exocyclic regioisomer being formed in
all cases with net cis addition of the aldehyde and the
silyl moiety. On the other hand, when a bulky substitu-
ent, such as a tert-butyl group, was present on the
substrate, longer reaction times (48 h, Table 2, entry 3)
and higher CO pressure (50 atm, Table 2, entry 4) were
necessary to improve the yield of silacyclane 6c.
The most interesting feature of these reactions is the
total diastereoselectivity of the intramolecular process if
a hindered substrate is reacted (Table 2, entries 2-4).
Actually, the presence of two chiral centers in 6b and 6c
5
3% yield (Scheme 3). The latter may arise by intra-
1
2
molecular carbometalation of 4 to generate 5 and
subsequent coupling with the chlorosilane as shown in
Scheme 3.
MePhSi(H)Cl was chosen as the silyl moiety precursor
since it introduces an asymmetric silicon center in the
ω-alkynes 1. Furthermore, it has been shown that the
silylformylation of alkynes with hydrosilanes bearing a
(the silicon and the carbon atom in the positions R to the
double bond) suggested the possibility of the formation
of two different diastereoisomers (cis and trans). Surpris-
ingly, when 3-tert-butyl-6-(methylphenylsilyl)-1-hexyne
(
1c) was submitted to intramolecular silylformylation,
only one diastereoisomer was detected. On the contrary,
when a methyl group was present on the alkynyl chain,
no diastereoselectivity was observed, both isomers being
formed in a 50:50 ratio (Table 2, entry 1).
NOE experiments performed on 6c indicated that the
aldehydic proton (CHO) was enhanced when the methyl
phenyl group (i.e., Me
2
PhSiH) proceeds approximately 10
5
times faster than that with trialkylsilanes (i.e., Et
At the beginning of this study, different rhodium
catalysts were tested, employing 6-(methylphenylsilyl)-
3
SiH).
1
-hexyne (1a ) as the model substrate, as shown in
Scheme 4. All experiments were performed according to
the following procedure: the ω-silylacetylene (1 mmol),
freshly distilled dichloromethane (25 mL), and the rhod-
ium complex (1 mmol %) were placed in a 40 mL stainless
steel autoclave. The reactor was flushed three times with
CO, pressurized to 20 atm of carbon monoxide, and
stirred at 40 °C for 24 h. Both the zwitterionic and
covalent complexes showed good catalytic activity, and
to the silicon atom (CH
vinylic proton (dCH) was enhanced when the tert-butyl
group ((CH C) was irradiated (Figure 1). Thus, a
-(formylmethylene)-1-silacyclohexane was formed with
a phenyl (Si) and a tert-butyl (C ) group in a trans
3
geometry.
To investigate the influence of the catalyst on the
stereoselectivity of the process, a different rhodium
species was used as the catalytic precursor in the
intramolecular silylformylation of 1c. In fact, the dia-
3
-Si) was irradiated and the
3 3
)
2
(
10) Cicogna, F. Synthesis of chiral R,ω-diynes and their use in the
Pauson-Khand cyclization reaction. M.S. Thesis in Chemistry. Uni-
versit a` di Pisa, Pisa, Italy, 1996.
(
11) (a) Knoess, H. P.; Furlong, M. T.; Rozema, M. J .; Knochel, P.
J . Org. Chem. 1991, 56, 5974. (b) Knochel, P.; Singer, D. Chem. Rev.
993, 2117.
12) Fujikura, S.; Ionue, M.; Utimoto, K.; Nozeki, H. Tetrahedron
Lett. 1984, 25, 1999.
(13) (a) Schrock, R. R.; Osborn, J . A. Inorg. Chem. 1970, 9, 2339.
(b) Amer, I.; Alper, H. J . Am. Chem. Soc. 1990, 112, 3674. Alper, H.;
Zhou, J . Q. J . Org. Chem. 1992, 57, 3729. (c) Alper, H.; Zhou, J . Q. J .
Org. Chem. 1992, 57, 3328. (d) Totland, K.; Alper, H. J . Org. Chem.
1993, 58, 3326.
1
(

Notes
J . Org. Chem., Vol. 64, No. 26, 1999 9713
tane anulation.22
Exp er im en ta l Section
Gen er a l Meth od s. IR spectra were measured on KBr plates
as neat films. 1H NMR (200 MHz) and C NMR (50.3 MHz)
13
3 4 3
spectra were recorded in CDCl solution with Me Si or CHCl
as internal standards. Mass spectra were obtained with a
Perkin-Elmer Q-Mass 910 connected to a Perkin-Elmer 8500 gas
chromatograph. GLC analyses were performed with a DB1
capillary column (30 m × 0.52 mm, 5 µm) using He as the carrier
gas and a flame ionization detector (FID). Column chromatog-
raphy was performed on silica gel 60 (230-400 mesh) purchased
from Fluka. All solvents were reagent-grade materials, pur-
chased by C. Erba, Fluka, and Merck, and purified by standard
methods. Tetrahydrofuran and mesitylene were distilled from
sodium immediately before use. Dichloromethane was distilled
F igu r e 1.
Sch em e 6
2 5
from P O and stored over molecular sieves. Methylphenylchlo-
rosilane (Fluka) was distilled under reduced pressure and stored
over molecular sieves. 1,2-Dibromoethane (Fluka) was used
2
3
+
4 7 8
without any further purification. Rh (CO)12 and [Rh C H -
-
13
BPh
4
]
were prepared according to published procedures.
2
acac was purchased from Aldrich.
sterocontrol detected in this specific case could be related
to the presence, in the zwitterionic complex, of bulky
groups such as BPh on the complexed arene ring. To test
3
this hypothesis, the cocondensate Rh/mesitylene, pre-
pared according to the metal vapor synthesis (MVS)
technique,14 was chosen as the catalyst since it exhibited
Rh(CO)
Gen er a l P r oced u r e for th e Syn th esis of 6-(Meth ylp h en -
ylsilyl)-1-h exyn es 1a -c. All reactions were carried out (at least
in duplicate) under a dry nitrogen atmosphere. To a THF
suspension of excess magnesium turnings (20 mmol), activated
with 1,2-dibromoethane, was added dropwise a mixture of the
3-alkyl-6-bromo-1-hexyne 2 (10 mmol) and chlorodimethylphe-
nylsilane (10 mmol). The reaction mixture was stirred for 3 h
at 40 °C, then hydrolyzed with excess water, and extracted with
high reactivity in the silylformylation reactions of vari-
ously branched acetylenes.15 The reaction of rhodium
2 4
pentane. The combined organic fractions were dried (Na SO ),
vapors with mesitylene affords the so-called solvated
metal atoms “solution”, which is considered to be formed
by highly reactive, small Rh metal clusters.16 In this case
no steric factors connected with the catalyst should affect
the stereoselectivity of the reaction. As shown in Scheme
filtered, and concentrated in vacuo (15-20 mmHg). The residual
oil, after purification by column chromatography using pentane
as eluant, gave pure 1a -c (Table 1).
-(Meth ylp h en ylsilyl)-1-h exyn e (1a ): IR 3294, 2110 cm-1;
H NMR δ 0.34 (d, 3H, J ) 3.8 Hz), 0.84-0.91 (m, 2H), 1.40-
1.70 (m, 4H), 1.92 (t, 1H, J ) 2.6 Hz), 2.19 (dt, 2H, J ) 7 and
7
6
1
6
, the activity and stereoselectivity of the MVS rhodium
2
7
8
1
.6 Hz), 4.35 (sext, 1H, J ) 3.8 Hz), 7.35-7.42 (m, 3H), 7.52-
.59 (m, 2H); 13C NMR δ -5.70, 12.89, 18.03, 23.50, 31.73, 68.17,
4.51, 127.87, 129.24, 134.29, 136.43; MS m/z (relative intensity)
catalyst is comparable with that of the zwitterionic
species, i.e., exclusive formation of trans-(Z)-2-(formyl-
methylidene)-3-tert-butyl-1-methyl-1-phenyl-1-silacyclo-
hexane (6c) being observed in both cases.
+
87 (M - 15, 13), 121 (100).
(
R)(S)-3-Meth yl-6-(m eth ylp h en ylsilyl)-1-h exyn e (1b): IR
-
1
1
In conclusion, both linear and branched ω-silylacety-
lenes can undergo intramolecular silylformylation reac-
tions in the presence of carbon monoxide and a rhodium
3306, 2117 cm ; H NMR δ 0.35 (d, 3H, J ) 3.8 Hz), 0.89 (t,
2
1
2
3
2
H, J ) 6.8 Hz), 1.16 and 1.18 (2d, 3H, J ) 6.9 and 5.8 Hz),
.24-1.60 (m, 4H), 2.16 and 2.18 (2d, 1H, J ) 2.4 and 3.3 Hz),
.34-2.52 (m, 1H), 4.34 (sext, 1H, J ) 3.8 Hz), 7.30-7.40 (m,
+
-
catalyst. The zwitterionic complex Rh (C
7
H
8
)BPh
4
and
13
H), 7.45-7.60 (m, 2H); C NMR δ -6.15, (13.07, 14.00), (20.91,
the Rh/mesitylene cocondensate are comparable in ef-
fectiveness (i.e., reactivity and stereoselectivity) and
catalyze a totally regio- and diastereoselective cyclization
if a sterically hindered alkynylsilane (1c) is used as the
reactant. The compounds 6a -c can be easily transformed
2.02), (25.32, 27.30), 29.23, (36.90, 40.01), 68.14, 88.85, 127.84,
+
129.20, 134.29; MS m/z (relative intensity) 201 (M - 15, 8),
121 (100).
(
R)(S)-3-ter t-Bu tyl-6-(m eth ylp h en ylsilyl)-1-h exyn e (1c):
-
1 1
IR 3308, 2113 cm ; H NMR δ 0.35 (d, 3H, J ) 3.9 Hz), 0.95 (s,
9
7
1
H), 1.20-1.85 (m, 6H), 2.00-2.10 (m, 2H), 4.36 (m, 1H), 7.30-
.40 (m, 3H), 7.48-7.57 (m, 2H); 13C NMR δ -5.61, (13.22,
3.31), (23.26, 23.19), 27.46, (32.70, 32.78), 33.11, 43.26, 70.48,
into dienes,17 dienones, and R,â-unsaturated ketones
18
19
and can be important precursors for the synthesis of more
2
0
complicated molecules via Peterson olefination, Nazarov
86.47, 127.81, 129.16, 134.30, 136.60; MS m/z (relative intensity)
type cyclopentenone anulation,21 or Trost type cyclopen-
+
243 (M - 15, 1), 121 (100).
Syn t h esis of [(Met h ylp h en ylsilyl)m et h ylen e]cyclo-
p en ta n e (3). Following the general procedure for the prepara-
tion of 6-(methylphenylsilyl)-1-hexynes 1a -c, 20 mmol of Mg
turnings, 10 mmol of 2a , and 10 mmol of chlorodimethylphen-
ylsilane were reacted at 60 °C for 5 h. After the usual workup,
(
14) (a) Blackborow, J . R.; Young, D. In Metal Vapour Synthesis in
Organometallic Chemistry; Springer-Verlag: New York, 1979. (b)
Klabunde, K. J . In Chemistry Of Free Atoms and Particles; Academic
Press: New York, 1980.
1
(
15) Aronica, L. A. Hydrosilylation and silylformylation of acetylenic
compounds. Ph.D. Thesis; Universit a` di Pisa: Pisa, Italy, 1999.
16) (a) Timms, P. L.; Turner, T. W. Adv. Organomet. Chem. 1977,
5, 53. (b) Klabunde, K. J .; Tanaka, Y. J . Mol. Catal. 1983, 21, 57. (c)
1.07 g (53%yield) of pure 3 was obtained: H NMR δ 0.43 (d,
3H, J ) 3.9 Hz), 1.63-1.77 (m, 4H), 2.30-2.48 (m, 4H), 4.67-
(
4
.75 (m, 1H), 5.54-5.59 (m, 1H), 7.35-7.43 (m, 3H), 7.54-7.65
1
+
(m, 2H); MS m/z (relative intensity) 202 (M , 5), 121(100). Anal.
Vitulli, G.; Uccello-Barretta, G.; Pannocchia, P.; Raffaelli, A. J .
Organomet. Chem. 1986, 302, C21. (d) Polizzi, C.; Caporusso, A. M.;
Vitulli, G.; Salvadori, P. J . Organomet. Chem. 1993, 451, C4.
Calcd for C13 18Si: C, 77.16; H, 8.97. Found: C, 77.28; H, 8.83.
H
Rh od iu m -Ca ta lyzed In tr a m olecu la r Silylfor m yla tion of
6-(Met h ylp h en ylsilyl)-1-h exyn es. Carbonylation reactions
were run in a 40 mL stainless steel autoclave containing a glass
liner. In a typical run, 1 mmol of 6-(methylphenylsilyl)-1-hexyne,
(17) (a) Martin, J .; Fleming, I.; Percival, A. J . Chem. Soc., Perkin
Trans. 1 1981, 2415. (b) Martin, J .; Fleming, I. J . Chem. Soc., Chem.
Commun. 1976, 679.
(18) Pillot, J .; Dunogues, J .; Calas, R. J . J . Chem. Res, Synop. 1977,
2
68.
(
(
(
19) Fleming, I.; Perry, D. A. Tetrahedron 1981, 37, 4034.
20) J ung, M. E.; Gaede, B. Tetrahedron 1979, 35, 621.
21) J ones, T. K.; Denmark, S. E. Helv. Chim. Acta 1983, 66, 2377.
(22) J ones, T. K.; Denmark, S. E. J . Am. Chem. Soc. 1982, 104, 2642.
(23) Martinengo, S.; Giordano, G.; Chini, P. Inorg. Synth. 1990, 28,
242.

9
714 J . Org. Chem., Vol. 64, No. 26, 1999
Notes
1
5 mL of freshly distilled dichloromethane, and 0.01 mmol of
(m, 1H), 6.62 (dd, 1H, J ) 8.3 and 1.2 Hz), 7.32-7.40 (m, 3H),
7.45-7.58 (m, 2H), 9.62 (d, 1H, J ) 8.3 Hz); 13C NMR δ 0.64,
12.70, 21.00, 29.09, 30.83, 35.09, 57.24, 128.42, 129.77, 133.99,
the rhodium catalyst were placed in the autoclave. The reactor
was flushed three times with CO and pressurized with carbon
monoxide. The reactor mixture was stirred for a specified period
of time at 40 °C, and then cooled to room temperature. After
removal of excess CO (fume hood) the reaction mixture was
diluted with pentane and filtered (Celite), and the solvent was
removed by rotary evaporation. The residue was purified by
column chromatography on silica gel using pentane/EtOAc
136.84, 143.76, 176.00, 193.69; MS m/z (relative intensity) 286
+
(M , 100). Anal. Calcd for C18
C, 75.25; H, 8.99.
H26SiO: C, 75.46; H, 9.15. Found:
Silylfor m yla tion of 3-ter t-bu tyl-6-(m eth ylp h en ylsilyl)-
-h exyn e Ca ta lyzed by Rh /Mesitylen e Cocon d en sa te. The
1
reaction was performed in a 25 mL stainless steel autoclave
fitted with a Teflon inner crucible and a stirring bar. A 0.258 g
(93:7) as eluant, affording pure 6a -c (Table 2, Schemes 4-6).
(
Z)-2-(F or m ylm eth ylid en e)-1-m eth yl-1-p h en yl-1-sila cy-
(1 mmol) sample of 1c, 1.5 mL of Rh/mesitylene cocondensate
-
1 1
cloh exa n e (6a ): IR 1675, 1428, cm ; H NMR δ 0.57 (s, 3H),
0
(0.01 mmol Rh), and 8.5 mL of freshly distilled dichloromethane
.75-1.30 (m, 2H), 1.60-1.90 (m, 4H), 2.46-2.70 (m, 2H), 6.43
were added, via syringe and under CO atmosphere, into a Pyrex
Schlenk” tube. This solution was introduced into the autoclave,
(dt, 1H, J ) 8.5 and 1.4 Hz), 7.33-7.43 (m, 3H), 7.50-7.57 (m,
“
2
2
1
H), 9.54 (d, 1H, J ) 8.5 Hz); 13C NMR δ -1.57, 14.43, 23.93,
previously placed under vacuum (0.1 mmHg), by a steel siphon.
The reactor was pressurized to 20 atm of CO, and the mixture
was stirred at 40 °C for 48 h. After removal of excess CO (fume
hood), the reaction mixture was diluted with pentane, filtered
9.96, 41.78, 128.48, 129.34, 133.90, 136.00, 141.34, 171.29,
+
93.69; MS m/z (relative intensity) 230 (M , 9), 187 (100). Anal.
Calcd for C14
Z)-2-(F or m ylm eth ylid en e)-1,3-d im eth yl-1-p h en yl-1-sila -
cycloh exa n e (6b): diastereomeric ratio 50:50; IR 1682, 1428
H18SiO: C, 72.99; H, 7.88. Found: C, 73.17; H, 7.92.
(
(Celite), and concentrated by bulb to bulb distillation (1 mmHg)
of the solvents. The residue was purified by column chromatog-
raphy on silica gel using pentane/EtOAc (93:7) as eluant,
affording 0.155 g (54%) of pure (Z)-2-(formylmethylidene)-3-tert-
butyl-1-methyl-1-phenyl-1-silacyclohexane (6c).
-
1 1
cm ; H NMR δ 0.55 and 0.58 (2s, 3H), 0.80-2.08 (m, 6H), 1.09
and 1.14 (2d, 3H, J ) 6.8 and 6.7 Hz), 2.53-2.79 (m, 1H), 6.43
and 6.51 (2dd, 1H, J ) 8.3 and 1.6 Hz), 7.30-7.40 (m, 3H), 7.45-
7
.60 (m, 2H), 9.44 and 9.75 (2d, 1H, J ) 8.3 Hz); 13C NMR δ
-
2.13, (14.14, 14.23), 20.44, (21.06, 21.15), 37.17, (42.15, 42.43),
128.35, 128.49), (129.67, 129.88), (133.77, 133.80), (136.48,
37.04), (138.96, 139.43), (174.55, 174.79), (193.90, 194.11); MS
Ack n ow led gm en t. We are grateful to the Natural
Sciences and Engineering Research Council of Canada
and to the Ministero dell’Universit a` e della Ricerca
Scientifica e Tecnologica (MURST)-Progetto Naz.le “Ste-
reoselezione in Sintesi Organica, Metodologie ed Appli-
cazioni” for support of this research.
(
1
+
m/z (relative intensity) 244 (M , 49), 137 (100). Anal. Calcd for
C
15
H
20SiO: C, 73.71; H, 8.25. Found: C, 74.02; H, 8.43.
(
Z)-2-(F or m ylm et h ylid en e)-1-m et h yl-1-p h en yl-3-(ter t-
bu tyl)-1-sila cycloh exa n e (6c): diastereomeric ratio 100:0; IR
1
1
-
1
1
668, 1429 cm
; H NMR δ 0.54 (s, 3H), 0.91 (s, 9H), 1.00-
.25 (m, 1H), 1.54-1.76 (m, 3H), 1.86-2.14 (m, 2H), 2.36-2.46
J O991129Y