Synthesis of 3-aryl-3-trimethylsilylcyclopropenes and their dibenzoyl derivatives. Possible cyclopropenyl anion precursors?

Article abstract of DOI:10.1039/A900376B

3-Aryl-3-trimethylsilylcyclopropenes (1) were synthesized by a four-step reaction sequence starting from known benzoyl trimethylsilanes. These cyclopropenes were thermalized on a gas chromatography column and the products were collected and identified. Their 1, 2-dibenzoyl derivatives (2) were prepared in a two-step transformation beginning with 3-aryl-1, 2, 3-tris(trimethylsilyl)cyclopropenes (5), the ultimate intermediates in the syntheses of 1. These compounds (2) are rare examples of isolable cyclopropenes with electron withdrawing groups at the vinyl positions. Fluoride-induced desilylation reactions of electron deficient cyclopropenes also are described and a carbon-centered electrophile has been successfully used to trap a putative cyclopropenyl anion.

Full text of DOI:10.1039/A900376B

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Synthesis of 3-aryl-3-trimethylsilylcyclopropenes and their
dibenzoyl derivatives. Possible cyclopropenyl anion precursors?†
Sangdon Han‡ and Steven R. Kass*
Department of Chemistry, University of Minnesota, Minneapolis, MN 55455, USA
Received (in Cambridge) 13th January 1999, Accepted 8th April 1999
3-Aryl-3-trimethylsilylcyclopropenes (1) were synthesized by a four-step reaction sequence starting from known
benzoyl trimethylsilanes. These cyclopropenes were thermalized on a gas chromatography column and the products
were collected and identified. Their 1,2-dibenzoyl derivatives (2) were prepared in a two-step transformation
beginning with 3-aryl-1,2,3-tris(trimethylsilyl)cyclopropenes (5), the ultimate intermediates in the syntheses of 1.
These compounds (2) are rare examples of isolable cyclopropenes with electron withdrawing groups at the vinyl
positions. Fluoride-induced desilylation reactions of electron deficient cyclopropenes also are described and a
carbon-centered electrophile has been successfully used to trap a putative cyclopropenyl anion.
Fluoride-induced desilylation reactions have been widely used
Cl
to efficiently cleave silicon–centered groups, and can generate
highly reactive species due to the strong silicon–fluorine bond.1,2
NaNH2
TMS
TMS
(1)
Consequently, 3-trimethylsilylcyclopropene derivatives are
THF
attractive cyclopropenyl anion precursors for gas-phase and
liquid-phase studies.3 3-Aryl-3-trimethylsilylcyclopropenes (1)
are of interest in this regard as they should be thermally stable,
the aryl group is a carbanion stabilizing substituent, and 1
should be a good substrate for adding additional stabilizing
groups to the vinyl position. These cyclopropenes maybe also
B –
TMS
TMS
useful for obtaining thermodynamic data on arylcyclo-
propenyl anions in the gas phase via the DePuy kinetic
method.4 In this paper we describe the synthesis and therm-
olysis products of 3-(p-tolyl)-3-trimethylsilylcyclopropene (1a)
and 3-(4-trifluoromethylphenyl)-3-trimethylsilylcyclopropene
(1b), and the conversion of these compounds to their 1,2-
dibenzoyl derivatives (2). The latter species represent rare
examples of stable cyclopropenes with electron withdrawing
(resonance stabilizing) groups at the vinyl positions. Some
fluoride-induced trapping experiments also were briefly
explored.
(2)
Br
R
R
TMS
1. p-TsNHNH2
2. n-BuLi
TMS
TMS
+
O
N2
TMS
3a: R = CH3
3b: = CF3
4a: R = CH3
4b: = CF3
hν
We recently reported the synthesis of 3-methyl-3-trimethyl-
silylcyclopropene5 and attempted to adapt this strategy to the
preparation of 3-phenyl-3-trimethylsilylcyclopropene. The key
cyclization step involving the reaction of (Z)-3-chloro-1-phenyl-
1-trimethylsilylpropene with sodium amide, however, failed to
produce the desired compound (eqn. 1). An alternative method,
the base-induced elimination of hydrogen bromide from
1-bromo-2-phenyl-2-trimethylsilylcyclopropane with t-BuOK–
DMSO, LDA–THF or t-BuOK under heterogeneous condi-
tions also was unsuccessful (eqn. 2).6
R
R
TBAF (2 equiv.)
TMS
TMS
TMS
TMS
1a: R = CH3
1b: = CF3
5a: R = CH3
5b: = CF3
Scheme 1
The successful synthesis of 3-(p-tolyl)-3-trimethylsilyl-
excess of bis(trimethylsilyl)acetylene led to the 3-aryl-1,2,3-
tris(trimethylsilyl)cyclopropenes (5) in 56 and 65% yields. Since
the vinyl hydrogens in a cyclopropene are much more acidic
than the allylic ones (pKa ~29 vs. 61),10 treatment of 5 with 2
equivalents of tetra-n-butylammonium fluoride (TBAF) select-
ively desilylated the trimethylsilyl groups at the vinyl positions
to afford the target compounds in 75 and 70% yields.11
cyclopropene
(1a)
and
3-(4-trifluoromethylphenyl)-3-
trimethylsilylcyclopropene (1b) was carried out as shown in
Scheme 1. Conversion of the known aryl trimethylsilyl ketones
(3)7 to their diazo compounds (4) was accomplished via their
toluene-p-sulfonyl hydrazones in overall yields of 65 and 74%.8,9
Photolysis of the aryl (trimethylsilyl)diazomethanes in a large
In the purification of 1a and 1b by preparative gas chroma-
tography, isomerization and dimerization occurred on a SE-30
column at 160 ЊC. The resulting products were found to be 3-
(trimethylsilyl)indene derivatives (6) and tricyclo[3.1.0.02,4]hex-
ane dimers (7) based upon spectroscopic analysis (1H and 13C
NMR as well as HRMS). Isomerization of cyclopropenes into
† 1H NMR spectra are available as supplementary data available from
BLDSC (SUPPL. NO. 57535, pp. 15) or the RSC Library. See Instruc-
tions for Authors available via the RSC web page (http:www.rsc.org/
authors).
‡ Current address: Department of Chemistry, University of California,
Berkeley, CA 94720-1468.
J. Chem. Soc., Perkin Trans. 1, 1999, 1553–1558
1553

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‡
R
R
R
1,5
a
b
c
1
H shift
TMS
TMS
TMS
6a: R = CH3
6b: = CF3
R
TMS
6
H
R
R
R
+
H
TMS
TMS
TMS
8a: R = CH3
8b: = CF3
9a: R = CH3
9b: = CF3
Ar
TMS
TMS
Ar
Ar
TMS
d
TMS
Ar
7a: Ar = p-C6H4CH3
7b: = p-C6H4CF3
Scheme 2
indenes is a well-known transformation which can be effected
by acid, heat or irradiation.12 This pathway is analogous to the
vinylcyclopropane–cyclopentene rearrangement and may occur
via a concerted reaction (Scheme 2, pathway a).13 The inter-
mediacy of a vinylcarbene in a thermal process has been estab-
lished in at least one case,14 so a stepwise process (pathway b) is
also quite possible. Strong evidence for vinylidenes in the
thermolysis of cyclopropenes has been reported as well.15
Apparently, this intermediate is not formed in this case to any
appreciable extent (pathway c) since it would be expected to
lead to 3-aryl-3-(trimethylsilyl)propynes (8) and 1-(trimethyl-
silyl)indenes (9), neither of which was obtained. A control
experiment also indicated that 9 (R = H)16 does not isomerize
to 6 (R = H) on the GC column at 160 ЊC.
R
TMS
1. TBAF (2 equiv.)
2. PhCHO (~50 equiv.)
5
Ph
Ph
OH
OH
10a: R = CH3
10b: = CF3
MnO2
CH2Cl2
R
A [2 ϩ 2] cyclization (pathway d in Scheme 2) leads to the
other thermolysis product (7). This type of dimerization is
known to be thermodynamically favorable because the cyclo-
addition across the cyclopropene double bonds reduces the ring
strain of the system by about 26 kcal molϪ1.17 Zeolites, Lewis
acids and transition metal complexes can effectively catalyze
this process which presumably occurs in a stepwise manner.18
The NMR spectra of 7 indicate that they have magnetically
equivalent aryl and trimethylsilyl groups. This is insufficient
information to assign the stereochemistry of the product, but
since every tricyclo[3.1.0.02,4]hexane derivative whose structure
has been determined to date is anti (undoubtedly, because the
syn isomer is much more strained),19 we infer that 7 is anti as
well. As for the arrangement of the aryl and trimethylsilyl sub-
stituents, the latter group is larger and should occupy both
equatorial (exo) positions. This assignment is in accord with an
X-ray crystal structure of 3-ethoxycarbonyl-3-trimethylsilyl-
cyclopropene dimer in which the trimethylsilyl groups occupy
the exo positions.20
Introduction of strong electron withdrawing groups on to
cyclopropene derivatives potentially can lead to stabilized
cyclopropenyl anion precursors.21 In this regard, both 1,2,3-
tris(trimethylsilyl)cyclopropenes (5) are of interest as they can
be converted into their 1,2-dibenzoyl derivatives.22 This was
accomplished by reacting cyclopropenes 5a and 5b with TBAF
in the presence of a large excess (~50 equiv.) of benzaldehyde in
anhydrous THF (Scheme 3). The resulting diols (10) were
TMS
Ph
Ph
O
O
2a: R = CH3
2b: = CF3
Scheme 3
formed as a mixture of four diastereomers in 42 and 44% yields.
Subsequent oxidation with activated manganese dioxide cleanly
provided the desired dibenzoyl cyclopropenes (2) in yields of 65
and 82%. 1,2-Dibenzoyl-3-methyl-3-trimethylsilylcyclopropene
recently was shown to undergo a concerted retro-ene reaction
(∆H‡ = 18.4 0.6 kcal molϪ1, ∆S‡ = Ϫ24.7 1.8 e.u. in tolu-
ene),5 and readily isomerized (t1/2 ~ 3 h) at 70 ЊC. In contrast,
the aryl analogues 2a and 2b can not rearrange via this pathway,
and only slowly decompose to unidentified products at 125 ЊC
in xylene. These compounds are rare examples of room
temperature stable cyclopropenes which have two resonance
stabilizing substituents at the vinyl positions.
Unfortunately, the TBAF mediated desilylation of 2 in the
presence of a large excess of benzaldehyde did not afford the
desired alcohols. Unidentified products were obtained instead,
presumably, because 2 undergoes a facile Michael addition. If
one uses poorer Michael acceptors at the vinyl positions as in
1554
J. Chem. Soc., Perkin Trans. 1, 1999, 1553–1558

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1,2,3-triphenyl-3-trimethylsilylcyclopropene, no reaction occurs
at room temperature and only protonolysis is observed under
forcing conditions.3a,6 In order to successfully trap a putative
cyclopropenyl anion with benzaldehyde a delicate balance must
be struck between stabilizing the incipient negative charge and
activating the cyclopropene double bond to nucleophilic attack.
filtered after being stirred in the dark at room temperature for 2
days. Ether was added to the filtrate which was then washed
with water and dried over anhydrous magnesium sulfate
(MgSO4). Evaporation of the solvent gave a red oil which pro-
vided 9.1 g (67%) of the diazo compound after vacuum distil-
1
lation: bp 58–61 ЊC (0.2 mm); H NMR (300 MHz, CDCl3)
3-Methoxycarbonyl-3-trimethylsilylcyclopropene20
is
not
δ 7.12 (dm, 2 H, J = 8.2 Hz), 6.93 (dt, 2 H, J = 8.4 and 1.8 Hz),
2.33 (s, 3 H), 0.36 (s, 9 H); 13C NMR (75 MHz, CDCl3) δ 132.9
(s), 130.0 (s), 129.8 (s), 129.7 (d), 122.9 (d), 20.9 (q), Ϫ0.93 (q);
IR (neat) 3023, 2959, 2928, 2038, 1610, 1565, 1509, 1284, 1253,
1176, 941, 843, 808 cmϪ1; HRMS-EI Mϩ Calcd for C11H16N2Si
204.1083, Found 204.1085; (M Ϫ N2)ϩ Calcd for C11H16Si
176.1022, Found 176.1016.
reactive enough, but its 1,2-diphenyl derivative gives a good
yield (78%) of the addition product (11, eqn. 3) along with a
OH
MeO2C
Ph
TMS
Ph
MeO2C
Ph
Ph
Ph
TBAF, PhCHO (excess)
THF
4-Trifluoromethylphenyl trimethylsilyl ketone tosylhydrazone8,9
11
~4
The procedure for the synthesis of p-tolyl trimethylsilyl ketone
tosylhydrazone was followed. In this case, 3.75 g (0.02 mol) of
toluene-p-sulfonyl hydrazide in 10 mL of methanol and 5.1 g
(0.02 mol) of [4-(trifluoromethyl)benzoyl]trimethylsilane in 6
mL of methanol were used, and the reaction mixture was
stirred for 1.5 h at 45 ЊC before being cooled to Ϫ10 ЊC. An 87%
MeO2C
Ph
H
+
(3)
Ph
12
1
1
yield (7.2 g) of the desired hydrazone was achieved: H NMR
small amount of the protodesilylated material (12) in a ratio of
ca. 4:1. These results suggest that it will be difficult to generate
a stable cyclopropenyl anion via a TBAF-induced desilylation.
More aggressive (and anhydrous) sources of fluoride, however,
are worth exploring. Studies along these lines are underway and
will be reported in due course.
(300 MHz, CDCl3) δ 7.76 (d, 2 H, J = 8.09 Hz), 7.65 (d, 2 H,
J = 8.2 Hz), 7.31 (d, 2 H, J = 8.01 Hz), 7.00 (d, 2 H, J = 8.08
Hz), 3.4 (s, 1 H), 2.44 (s, 3 H), 0.09 (s, 9 H); 19F NMR (282
MHz, CDCl3, CFCl3 = δ 0.00) δ Ϫ63.3 (s); 13C NMR (75 MHz,
CDCl3) δ 166.6 (s), 144.2 (s), 138.5 (s), 135.3 (s), 130.8 (s; q,
2JC–F = 32.6 Hz), 129.5 (d), 127.9 (d), 126.6 (d), 126.5 (d; q,
3JC–F = 3.0 Hz), 123.6 (s; q, 1JC–F = 272.2 Hz), 21.6 (q), Ϫ2.5 (q);
IR (KBr) 3188, 3065, 2955, 2894, 1616, 1406, 1384, 1328, 1252,
1160, 1126, 1068, 870, 848, 680 cmϪ1.
Experimental
General methods
(4-Trifluoromethylphenyl)trimethylsilyldiazomethane 4b8,9
All glassware was soaked in a base bath (KOH–isopropyl
alcohol) for at least 12 h, washed with water and either oven
dried or flame dried prior to use. Solvents and reagents were
dried and purified using standard non-acidic methods. Boiling
points given for materials distilled under argon or nitrogen are
uncorrected for differences in atmospheric pressure.
Nuclear magnetic resonance (NMR) spectra were recorded
with a Varian VXR-300, Unity 500, or Bruker AC300 spec-
trometer and are reported in ppm (δ). Infrared spectra were
obtained with a Mattson Instruments Polaris FT-IR spec-
trometer and are reported in wavenumbers (cmϪ1). High reso-
lution mass spectra were recorded on a Finnigan MAT 95 mass
spectrometer or a Finnigan 2001-DD FTMS. Preparative gas
chromatography was carried out on a Varian 700 Aerograph
chromatograph with helium as the carrier gas.
An LDA solution (0.0156 mol in 40 mL of anhydrous THF)
was prepared at Ϫ10 ЊC by reacting 6.24 mL of 2.5 M n-BuLi
with 2.3 mL of diisopropylamine. The resulting solution was
transferred to an addition funnel and was added dropwise
under nitrogen at Ϫ78 ЊC to 6.5 g (0.0156 mol) of the appropri-
ate hydrazone in 100 mL of anhydrous THF. After 3 h the
mixture was allowed to warm to room temperature and the
solvent was removed under reduced pressure. The solid residue
was heated to 100 ЊC at a pressure of 0.2 mm and 3.4 g (85%) of
the diazomethane was obtained as a red oil: bp 60–62 ЊC (0.2
mm); 1H NMR (300 MHz, CDCl3) δ 7.52 (d, 2 H, J = 8.4 Hz),
7.08 (d, 2 H, J = 8.4 Hz), 0.38 (s, 9 H); 19F NMR (282 MHz,
CDCl3, CFCl3 = δ 0.00) δ Ϫ62.53 (s); 13C NMR (75 MHz,
3
CDCl3) δ 138.6 (s), 125.8 (d; q, JC–F = 3.6 Hz), 125.0 (s; q,
2JC–F = 32.5 Hz), 124.4 (s; q, 1JC–F = 271 Hz), 122.5 (d), 120.9 (s),
Ϫ1.06 (q); IR (neat) 2964, 2049, 1612, 1515, 1414, 1331, 1284,
1256, 1165, 1119, 1070, 1012, 941, 842, 756 cmϪ1; HRMS-EI
Mϩ Calcd for C11H13F3N2Si 258.0800, Found 258.0807,
(M Ϫ N2)ϩ; Calcd for C11H13F3Si 230.0739, Found 230.0734.
p-Tolyl trimethylsilyl ketone tosylhydrazone9
4-Methylbenzoyltrimethylsilane (3a, 14.0 g, 0.073 mol)7 in 10
mL of methanol was added to a suspension of toluene-p-
sulfonyl hydrazide (13.5 g, 0.073 mol) in 25 mL of methanol.
The mixture was stirred for 1 h at 45 ЊC and then cooled to
Ϫ10 ЊC. The solid product was filtered and washed with a small
amount of cold methanol to give 25.6 g (97%) of the hydrazone
Bis(trimethylsilyl)acetylene
A 2.5 M solution of n-BuLi (40.8 mL, 0.102 mol) was added
dropwise to 10 g (0.102 mol) of trimethylsilylacetylene23 in 200
mL of anhydrous THF at Ϫ78 ЊC. The reaction was stirred for
40 min at Ϫ78 ЊC and then 15.4 mL (1.2 equiv.) of TMSCl was
slowly added. The resulting mixture was stirred for an addi-
tional 1 h at Ϫ78 ЊC before allowing it to slowly warm up to
room temperature. HCl (50 mL 1 M) and then 100 mL of water
were used to quench the reaction, subsequently, the aqueous
layer was extracted with pentane (3 × 100 mL). The combined
organic material was washed with water (10 × 60 mL) and dried
over anhydrous MgSO4. Fractional distillation provided 15.6 g
(90%) of the disubstituted acetylene: 1H NMR (300 MHz,
CDCl3) δ 0.16 (s); 13C NMR (75 MHz, CDCl3) δ 113.7 (s),
Ϫ0.06 (q); IR (neat) 2962, 2901, 1409, 1251, 1033, 842 cmϪ1.
1
as a white solid: H NMR (300 MHz, CDCl3) δ 7.75 (d, 2 H,
J = 8.1 Hz), 7.65 (br s, 1 H), 7.28 (d, 2 H, J = 8.1 Hz), 7.17 (d,
2 H, J = 8.1 Hz), 6.72 (d, 2 H, J = 8.1 Hz), 2.41 (s, 3 H), 2.31 (s,
3 H), 0.07 (s, 9 H); 13C NMR (75 MHz, CDCl3) δ 168.8 (s),
143.9 (s), 138.7 (s), 135.5 (s), 131.4 (s), 130.2 (d), 129.4 (d), 127.9
(d), 125.8 (d), 21.6 (q), 21.2 (q), Ϫ2.3 (q); IR (KBr) 3195, 3064,
3044, 2964, 1915, 1669, 1598, 1497, 1402, 1330, 1158, 1094, 850,
813, 684 cmϪ1.
(p-Tolyl)trimethylsilyldiazomethane 4a9
The requisite hydrazone (25.0 g, 0.069 mol) in 500 mL of
anhydrous THF was cooled to 0 ЊC and then 27.6 mL of 2.5 M
n-BuLi (0.069 mol) was slowly added. The reaction mixture was
J. Chem. Soc., Perkin Trans. 1, 1999, 1553–1558
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3-(p-Tolyl)-1,2,3-tris(trimethylsilyl)cyclopropene 5a
3-(4-Trifluoromethylphenyl)-1,2,3-tris(trimethylsilyl)cyclo-
propene 5b
Bis(trimethylsilyl)acetylene (27 g, 0.159 mol) was combined
with 0.9 g (4.4 mmol) of (p-tolyl)trimethylsilyldiazomethane
and the solution was degassed with nitrogen before being
irradiated at room temperature with a 450 W slide projection
lamp for 1 day. Infrared spectroscopy was used to monitor the
progress of the reaction and when 4a was consumed the excess
bis(trimethylsilyl)acetylene was removed by distillation under
reduced pressure (~20 mm) at ~70 ЊC. The remaining material
was chromatographed on a silica gel column using pentane as
the eluting solvent to afford 0.84 g (56%) of the cyclopropene as
a liquid: 1H NMR (500 MHz, CDCl3) δ 6.98 (br m, 4 H), 2.28 (s,
3 H), 0.18 (s, 18 H), 0.008 (s, 9 H); 13C NMR (75 MHz, CDCl3)
δ 147.8 (s), 135.9 (s), 130.2 (s), 128.4 (d), 127.5 (d), 37.1 (s),
20.9 (q), Ϫ0.34 (q), Ϫ0.39 (q); IR (neat) 3048, 2957, 2896,
1885, 1724, 1508, 1406, 1248, 893, 838, 756 cmϪ1; HRMS-CI (iso-
butane) Mϩ Calcd for C19H34Si3 346.1968, Found 346.1988;
M ϩ Hϩ Calcd for C19H35Si3 347.2047, Found 347.2031.
The procedure for the synthesis of 5a was followed. In this case,
0.7 g (2.7 mmol) of 4b in 26 g of bis(trimethylsilyl)acetylene was
irradiated for 23 h to afford 0.71 g (65%) of the desired cyclo-
1
propene: bp 85–88 ЊC (0.1 mm); H NMR (300 MHz, CDCl3)
δ 7.43 (d, 2 H, J = 8.4 Hz), 7.18 (d, 2 H, J = 8.4 Hz), 0.20 (s, 18
H), 0.054 (s, 9 H); 19F NMR (282 MHz, CDCl3, CFCl3 = δ 0.00)
δ Ϫ62.3 (s); 13C NMR (75 MHz, CDCl3) δ 155.7 (s), 134.6 (s),
127.4 (d), 126.0 (s; q, 2JC–F = 32.3 Hz§), 124.7 (s; q, 1JC–F = 271.6
Hz), 124.5 (d; q, 3JC–F = 3.6 Hz), 21.0 (s), Ϫ0.31 (q), Ϫ0.48 (q);
IR (neat) 3069, 2957, 2900, 1885, 1730, 1612, 1407, 1328, 1164,
1123, 1069, 1016, 843 cmϪ1; HRMS-CI (isobutane) Mϩ Calcd
for C19H31F3Si3 400.1685, Found 400.1670; M ϩ Hϩ Calcd for
C19H32F3Si3 401.1764, Found 401.1721.
3-(4-Trifluoromethylphenyl)-3-trimethylsilylcyclopropene 1b
The procedure for the synthesis of 1a was followed. In this case,
0.2 g (0.5 mmol) of 5b in 9 mL of THF and 1 mL (2 equiv.) of
1.0 M TBAF were used, and 0.09 g (70%) of liquid cyclo-
propene was obtained: 1H NMR (300 MHz, CDCl3) δ 7.47 (d,
2 H, J = 8.0 Hz), 7.40 (s, 2 H), 7.21 (d, 2 H, J = 8.0 Hz), Ϫ0.007
(s, 9 H); 19F NMR (282 MHz, CDCl3, CFCl3 = δ 0.00) δ Ϫ62.57
(s); 13C NMR (75 MHz, CDCl3) δ 153.8 (s), 127.9 (d), 127.2
3-(p-Tolyl)-3-trimethylsilylcyclopropene 1a
3-(p-Tolyl)-1,2,3-tris(trimethylsilyl)cyclopropene (0.15 g, 0.43
mmol) was dissolved in 8 mL of anhydrous THF under an
argon atmosphere and 1.53 mL (3 equiv.) of 1 M TBAF in THF
was added to it at room temperature. The solution quickly
changed to a dark reddish color and was stirred for an add-
itional 20 min before being quenched with water. The product
was extracted with pentane (3 × 15 mL) and the combined
organic material was washed with water and dried over
anhydrous MgSO4. Removal of the solvent with a rotary evap-
orator at ~0 ЊC was followed by column chromatography (pen-
2
3
(s; q, JC–F = 32.3 Hz), 125.1 (d; q, JC–F = 3.6 Hz), 124.5 (s; q,
1JC–F = 271.6 Hz), 113.2 (d), 18.8 (s), Ϫ1.68 (q); IR (neat) 3116,
2959, 2899, 1647, 1613, 1406, 1326, 1250, 1164, 1124, 1066,
1014, 943, 840 cmϪ1; HRMS-CI (isobutane) Mϩ Calcd for
C13H15F3Si 256.0895, Found 256.0906; M ϩ Hϩ Calcd for
C13H16F3Si 257.0973, Found 257.0927.
1
tane) to yield 0.066 g of 1a (75%) as a liquid: H NMR (300
1,2-Dibenzoyl-3-(4-trifluoromethylphenyl)-3-trimethylsilylcyclo-
propene 2b
MHz, CDCl3) δ 7.38 (s, 2 H), 7.05 (br s, 4 H), 2.31 (s, 3 H), 0.004
(s, 9 H); 13C NMR (75 MHz, CDCl3) δ 146.4 (s), 134.4 (s), 128.9
(d), 127.5 (d), 113.6 (d), 20.9 (q), 18.0 (s), Ϫ1.54 (q); IR (neat)
3104, 3028, 2955, 2923, 2854, 1656, 1510, 1454, 1247, 1108, 837,
735 cmϪ1; HRMS-EI Mϩ Calcd for C13H18Si 202.1177, Found
202.1162.
The procedure for the synthesis of 2a was followed. In this case,
a solution of 0.32 g (0.8 mmol) of 5b and 4.5 g of benzaldehyde
(42 mmol) in 12 mL of THF was treated with 1.4 mL (2 equiv.)
of 1 M TBAF. The resulting diol (10b) was obtained as a mix-
ture of three diastereomers in a 44% yield (0.11 g). After MnO2
oxidation of 10b, 0.09 g (82%) of 2b was realized as a yellow oil:
1H NMR (300 MHz, CDCl3) δ 7.90 (m, 4 H), 7.56–7.53 (m,
6 H), 7.36 (m, 4 H), 0.15 (s, 9 H); 19F NMR (282 MHz, CDCl3,
CFCl3 = δ 0.00) δ Ϫ62.79 (s); 13C NMR (75 MHz, CDCl3)
δ 184.9 (s), 148.9 (s), 135.7 (s), 134.5 (d), 129.3 (d), 129.0 (d),
1,2-Dibenzoyl-3-(p-tolyl)-3-trimethylsilylcyclopropene 2a
To a solution of 0.28 g (0.8 mmol) of 5a and 4.5 g (42 mmol) of
benzaldehyde in 12 mL of anhydrous THF was added 2.4 mL
(3 equiv.) of 1 M tetra-n-butylammonium fluoride (TBAF) at
room temperature under an argon atmosphere. The reaction
mixture was stirred for an additional 6 h, quenched with water,
and extracted with ether (3 × 20 mL). The combined organic
material was washed with water, dried over anhydrous mag-
nesium sulfate, and concentrated under reduced pressure to
afford the crude diol (10a). Purification by column chrom-
atography (100% hexane to 80% hexane and 20% ether) gave
0.14 g (42%) of the desired product as a mixture of three
diastereomers. The individual compounds were not separated,
and the mixture of diols was used for the subsequent oxidation.
Dichloromethane (10 mL) and 0.1 g of 10a was treated with
0.42 g (20 equiv.) of activated MnO2 at 0 ЊC under an argon
atmosphere. The resulting heterogeneous solution was stirred
for an additional 40 min at 0 ЊC and then was filtered through a
plug of silica gel. Removal of the solvent under reduced pres-
sure gave the crude dibenzoyl cyclopropene which was purified
by chromatography using a silica gel column (100% hexane to
95% hexane and 5% ether) to yield 0.06 g (60%) of 2a as a
yellow oil: 1H NMR (500 MHz, CDCl3) δ 7.95 (dd, 4 H, J = 8.5
Hz and 1.5 Hz), 7.54 (tt, 2 H, J = 7.5 Hz and 1.5 Hz), 7.37 (dd,
4 H, J = 8.5 Hz and 7.5 Hz), 7.31 (d, 2 H, J = 8.5 Hz), 7.10 (d,
2 H, J = 8.5 Hz), 2.32 (s, 3 H), 0.15 (s, 9 H); 13C NMR (75 MHz,
CDCl3) δ 185.3 (s), 141.6 (s), 135.99 (s), 135.95 (s), 134.2 (d),
129.4 (d), 129.3 (d), 128.7 (d), 128.4 (d), 127.9 (s), 37.9 (s), 21.2
(q), Ϫ1.29 (q); HRMS-CI (isobutane) Mϩ Calcd for C27H26O2Si
410.1701, Found 410.1694.
2
128.8 (d), 128.6 (s; q, JC–F = 32.4 Hz), 126.6 (s), 125.6 (d;
q, 3JC–F = 3.6 Hz), 124.3 (s; q, 1JC–F = 272.2 Hz), 37.3 (s), Ϫ1.49
(q); IR (neat) 3062, 2961, 2934, 1795, 1642, 1614, 1598, 1580,
1450, 1326, 1252, 1165, 1125, 1067, 845 cmϪ1; HRMS-CI
(isobutane) Mϩ Calcd for C27H23F3O2Si 464.1419; Found
464.1419.
Thermal isomerization and dimerization of 1a and 1b
The cyclopropenes were injected into a preparative gas chro-
matograph on to a 10% SE-30 on Chrom W column at 160 ЊC.
Two main products, an indene and a dimer, were obtained.
Intramolecular isomerization afforded the solid indene, which
eluted in 15 min. The intermolecular [2 ϩ 2] cyclization dimer
was attained as a white solid after trapping the effluent for
about 12 h. A small amount of 1b also was recovered after 10
min, whereas 1a was completely consumed under the same
conditions.
6-Methyl-3-trimethylsilylindene 6a
1H NMR (300 MHz, CDCl3) δ 7.37 (d, 1 H, J = 7.5 Hz), 7.32 (br
s, 1 H), 7.10 (d, 1 H, J = 7.5 Hz), 6.69 (t, 1 H, J = 1.8 Hz), 3.38
(m, 2 H), 2.39 (s, 3 H), 0.29 (s, 9 H); 13C NMR (75 MHz,
§ Quaternary carbon (s) split by fluorine into a quartet.
1556
J. Chem. Soc., Perkin Trans. 1, 1999, 1553–1558

View Article Online
CDCl3) δ 145.4 (s), 145.0 (s), 144.9 (s), 143.1 (d), 133.9 (s), 126.8
(d), 124.7 (d), 121.5 (d), 40.5 (t), 21.4 (q), Ϫ1.1 (q); IR (neat)
3024, 3005, 2957, 2897, 1731, 1611, 1472, 1387, 1249, 1106,
1035, 985, 838 cmϪ1; HRMS-CI (isobutane) Mϩ Calcd for
C13H18Si 202.1177, Found 202.1175.
washed with water, dried over anhydrous magnesium sulfate,
and concentrated in vacuo. After column chromatography
(100% hexane to 80% hexane and 20% dichloromethane) 60
mg (78%) of 3-methoxycarbonyl-3-[phenyl(hydroxy)methyl]-
1
1,2-diphenylcyclopropene (11) was obtained: H NMR (500
MHz, CDCl3) δ 7.68 (dm, 2 H, J = 8.0 Hz), 7.49–7.33 (m, 8 H),
7.13 (dm, 2 H, J = 8.0 Hz), 7.05 (m, 3 H), 5.77 (d, 1 H, J = 4.5
Hz), 3.76 (d, 1 H, J = 4.5 Hz), 3.63 (s, 3 H); 13C NMR (75 MHz,
CDCl3) δ 176.2 (s), 141.1 (s), 130.3 (d), 129.7 (d), 129.4 (d),
129.2 (d), 128.8 (d), 128.7 (d), 127.7 (d), 127.2 (d), 127.1 (s),
126.8 (d), 126.6 (s), 110.2 (s), 108.7 (s), 75.7 (d), 52.1 (q), 38.1
(s); IR (KBr) 3463, 3020, 2951, 2913, 2913, 1698, 1495,
1446, 1433, 1396, 1266, 1177, 1060, 1023, 758 cmϪ1; HRMS
(MALDI, DHBA matrix) (M ϩ Na)ϩ Calcd for C24H20O3Na
379.1305, Found 379.1307. 3-Methoxycarbonyl-1,2-diphenyl-
anti-3,6-Bis(4-methylphenyl)-3,6-bis(trimethylsilyl)tricyclo-
[3.1.0.02,4]hexane (7a)
1H NMR (500 MHz, CDCl3) δ 7.05 (br s, 8 H), 2.32 (s, 6 H),
1.44 (s, 4 H), Ϫ0.31 (s, 18 H); 13C NMR (75 MHz, CDCl3)
δ 137.7 (s), 133.7 (s), 130.1 (d), 128.2 (d), 38.2 (s), 27.3 (d), 21.1
(q), Ϫ3.2 (q); IR (KBr) 3032, 2958, 1617, 1509, 1385, 1248,
1102, 1066, 978, 876, 834 cmϪ1; HRMS-CI (isobutane) Mϩ
Calcd for C26H36Si2 404.2355; Found 404.2353.
1
cyclopropene (12) was also obtained as a minor product: H
6-Trifluoromethyl-3-trimethylsilylindene (6b)
NMR (300 MHz, CDCl3) δ 7.69 (dm, 4 H, J = 7.2 Hz), 7.48 (tm,
4 H, J = 7.5 Hz), 7.40 (tm, 2 H, J = 7.5 Hz), 3.71 (s, 3 H), 2.84 (s,
1 H); 13C NMR (75 MHz, CDCl3) δ 175.4 (s), 130.0 (d), 129.4
(d), 128.9 (d), 127.0 (s), 107.5 (s), 51.8 (q), 21.4 (d); HRMS (EI)
Mϩ Calcd for C17H14O2 250.0993, Found 250.0982.
1H NMR (300 MHz, CDCl3) δ 7.74 (br s, 1 H), 7.55–7.54 (d, 2
H, J = 0.9 Hz), 6.92 (t, 1 H, J = 1.9 Hz), 3.48 (dd, 2 H, J = 1.8
Hz and 0.9 Hz), 0.32 (s, 9 H); 19F NMR (282 MHz, CDCl3,
CFCl3 = δ 0.00) δ Ϫ61.84 (s); 13C NMR (75 MHz, CDCl3)
δ 151.4 (s), 146.8 (d), 144.9 (s), 126.5 (s), 126.4 (s; q, 2JC–F = 31.8
1
3
Hz), 124.9 (s; q, JC–F = 271.6 Hz), 123.5 (d; q, JC–F = 3.7 Hz),
121.7 (d), 120.4 (d; q, JC-F = 4.3 Hz), 40.8 (t), Ϫ1.23 (q); IR
(KBr) 2972, 2963, 1625, 1432, 1385, 1334, 1279, 1249, 1155,
1113, 1059, 887, 838 cmϪ1; HRMS-EI Mϩ Calcd for C13H15F3Si
256.0895, Found 256.0896.
Acknowledgements
We thank Katherine M. Broadus for her assistance in obtaining
some of the spectral data, synthesizing 1-(trimethylsilyl)indene
and running a control experiment. Support from the National
Science Foundation, the donors of the Petroleum Research
Foundation, as administered by the American Chemical
Society, are gratefully acknowledged.
anti-3,6-Bis(4-trifluoromethylphenyl)-3,6-bis(trimethylsilyl)-
tricyclo[3.1.0.02,4]hexane (7b)
1H NMR (300 MHz, CDCl3) δ 7.53 (d, 4 H, J = 8.4 Hz), 7.27 (d,
4 H, J = 8.4 Hz), 1.51 (s, 4 H), Ϫ0.29 (s, 18 H); 19F NMR (282
MHz, CDCl3, CFCl3 = δ 0.00) δ Ϫ62.48 (s); 13C NMR (75
MHz, CDCl3) δ 145.3 (s), 130.3 (d), 127.1 (s; q, 2JC–F = 32.4 Hz),
124.7 (d; q, JC–F = 3.6 Hz), 124.6 (s; q, JC–F = 271.6 Hz), 46.6
(s), 27.6 (d), Ϫ3.3 (q); IR (KBr) 3039, 3023, 2963, 2904, 1616,
1409, 1325, 1272, 1250, 1165, 1117, 1067, 1016, 980, 874, 845
cmϪ1; HRMS-CI (isobutane) Mϩ Calcd for C26H30F6Si2
512.1790, Found 512.1782.
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3-Methoxycarbonyl-1,2-diphenyl-3-trimethylsilylcyclopropene
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Hz), 7.46 (t, 4 H, J = 7.5 Hz), 7.36 (t, 2 H, J = 7.5 Hz), 3.66 (s, 3
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J. Chem. Soc., Perkin Trans. 1, 1999, 1553–1558
1557

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Paper 9/00376B
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J. Chem. Soc., Perkin Trans. 1, 1999, 1553–1558