Structural Characterization and Unique Catalytic Performance of Silyl-Group-Substituted Geminal Dichromiomethane Complexes Stabilized with a Diamine Ligand

Article abstract of DOI:10.1021/jacs.7b07487

Stabilization by a silyl group on the methylene carbon and a diamine ligand led to the isolation of gem-dichromiomethane species. X-ray crystallography confirmed the identity of the structure of this rare example of reactive gem-dimetalloalkane species. T

Full text of DOI:10.1021/jacs.7b07487

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Article
Structural Characterization and Unique Catalytic
Performance of Silyl Group-Substituted Geminal
Dichromiomethane Complexes Stabilized with a Diamine Ligand
Masahito Murai, Ryuji Taniguchi, Naoki Hosokawa, Yusuke
Nishida, Hiroko Mimachi, Toshiyuki Oshiki, and Kazuhiko Takai
J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.7b07487 • Publication Date (Web): 16 Aug 2017
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Journal of the American Chemical Society
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Structural Characterization and Unique Catalytic Performance
of Silyl Group-Substituted Geminal Dichromiomethane Com-
plexes Stabilized with a Diamine Ligand
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Masahito Murai,*,† Ryuji Taniguchi,† Naoki Hosokawa,† Yusuke Nishida,† Hiroko Mimachi,† Toshiyuki
Oshiki,† and Kazuhiko Takai*,†, ‡
†Division of Applied Chemistry, Graduate School of Natural Science and Technology, and ‡Research Institute for Interdisci-
plinary Science, Okayama University, 3-1-1 Tsushimanaka, Kita-ku, Okayama 700-8530, Japan
KEYWORDS: Chromium, Geminal Dimetallomethane, Cyclopropanation, Alkylidenation
ABSTRACT: Stabilization by a silyl group on the methylene carbon and a diamine ligand let to the isolation of gem-
dichromiomethane species. X-ray crystallography confirmed the identity of the structure of this rare example of reactive gem-
dimetalloalkane species. The isolated gem-dichromiomethane complex acted as a storable silylmethylidene carbene equivalent, with
reactivity that could be changed dramatically upon addition of a Lewis acid (ZnCl2) and a base (TMEDA) to promote both silyl-
alkylidenation of polar aldehydes and silylcyclopropanation of non-polar alkenes. Identification of a key reactive species also iden-
tified the catalytic version of these transformations, and provided insights into the reaction mechanism. In contrast to Simmons-
Smith cyclopropanation, the real reactive species for the current cyclopropanation was a chromiocarbene species, not a chromium
carbenoid species.
silanes, and boranes. Therfore, the method has been applied to
the total synthesis of many natural products.8 Later studies
■ INTRODUCTION
Bench-stable gem-dimetalloalkanes (R2CM1M2) possessing
two metal atoms on the same carbon are useful synthons
equivalent to dianions.1 The classic example is a Tebbe
reagent (TiCH2Al), which is a widely used organometallic
reagent for methylenation of carbonyl compounds.2 In contrast
to their synthetic potential, however, the variety and number of
structurally characterized reactive gem-dimetalloalkanes are
limited, probably due to their instability.3 The isolation and
direct structural characterization of these compounds is chal-
lenging; however, a recent our report indicated that the use of
a sterically hindered bipyridyl ligand enabled isolation and
showed
a dramatically different reaction course, with
cyclopropanes obtained from alkenes upon treatment of CrCl2
with a proper diamine ligand (Scheme 1(b)).9 Compared with
typical cyclopropanation protocols, including Simmons-Smith
type cyclopropanation with zinc carbenoids (RZnCH2X), and
catalytic decomposition of diazo compounds with appropriate
metal catalysts,10,11 this approach easily provides functional-
ized cyclopropanes containing iodo, silyl, and boryl groups in
a single step from commercially available olefins.
structural
characterization
of
a
new
gem-
di(iodozincio)methane complex.4 Based on this successful
result, an approach involving the use of bulky functional
groups to kinetically stabilize the reactive methylene center
was envisioned to be a useful strategy for identifying other
gem-dimetalloalkane species for organic synthesis.
Organochromium reagents are among the growing number
of organometallic reagents with unique reactivity.5 They offer
significant benefits for carboncarbon bond-forming reactions,
including allylation, nickel-catalyzed alkenylation, radical
coupling reactions, and oligo- or polymerization of ethylene.5
Recently, CrCl2 was also shown act as a useful catalyst for
cross-coupling of arylhalides with Grignard reagents by
Knochel and coworkers.5j Another traditional but unique use
of chromium reagents is in the alkylidenation of aldehydes.6,7
Takai reported that the use of organochromium reagents pre-
pared from CrCl2 and di- or trihalomethanes (RCHX2), con-
verted aldehydes into functionalized alkenes in good yields
(Scheme 1(a)).7 The reaction proceeded under mild conditions
with excellent stereoselectivity and functional group
compatibility to provide synthetically useful alkenyl iodides,
Scheme
1.
Impact
of
TMEDA
(N,N,N’,N’-
tetramethylethylenediamine) on chromium-promoted iodoal-
kylidenation of olefins and iodocyclopropanation of alkenes
While gem-di(dichlorochromio)methanes, XCH(CrCl2)2 (X
= I, SiR3, and Bpin), were proposed as reactive species in the
previous studies,9a-c isolation and direct structural
characterization have remained elusive. The unique reactivity
shown
in
Scheme
1
implies
that
gem-
di(dichlorochromio)methane reagents themselves tend to react
with polar carbonheteroatom double bonds of aldehydes,
while treatment of diamine additives changes reactivity prefer-
entially toward the non-polar carboncarbon double bonds of
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alkenes. This finding indicated that isolation and direct struc-
tural characterization of chromium intermediates could pro-
vide insights into the origin of the reactivity and expand the
application of organochromium reagents.
Page 2 of 10
complex 1 was treated with (diiodomethyl)trimethylsilane
(here after referred to as “SiCHI2”)15 to yield
(tmeda)SiCH(CrCl2)2 complex 2 along with the generation of
(tmeda)CrCl2I as a byproduct via two consecutive single-
electron transfers of 1 (Scheme 3). Pure 2 was isolated in 57%
yield as a red solid by extraction of the crude mixture with
dichloromethane and hexane (v / v = 3 / 2), followed by re-
moval of organic solvents under reduced pressure. Although
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The present study describes the synthesis and identification
of a storable gem-di(dichlorochromio)methane complex kinet-
ically stabilized with a diamine ligand and a bulky trimethylsi-
lyl (SiMe3) group on the methylene carbon. The stability as
well as the catalytic performance of the gem-
dichromiomethane complex for both cyclopropanation and
alkylidenation was investigated. The kinetic study provided
useful insights into the effect of diamine ligands and the nature
of the unique dinuclear chromium reactive intermediate for
silylcyclopropanation.12 These studies also revealed unique
reactivity control of the gem-dichromiomethane species by a
Lewis acid (ZnCl2) and Lewis base (TMEDA). Similar reac-
tivity control of gem-dimetallomethanes was reported previ-
ously by Grubbs and coworkers,13 who stated that the Tebbe
reagent promoted the methylenation of aldehydes, while titan-
acarbene species generated by addition of 4-
(dimethylamino)pyridine (DMAP) promoted olefin metathesis
polymerization (Scheme 2). In the current reaction, gem-
dichromiomethane itself promoted alkylidenation of aldehydes,
while cyclopropanation of alkenes occurred via pretreatment
of TMEDA. Similar reactivity control is very rare for gem-
dimetallomethanes.
1
the H NMR spectra for 1 and 2 displayed only broad reso-
nance due to the paramagnetic nature of chromium compounds,
elemental analysis supported the structural formula of these
complexes (see Experimental Section for details).
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Scheme 3. Synthesis of (tmeda)SiCH(CrCl2)2 complex 2
Figure 1. X-ray crystal structure of (tmeda)CrIICl2 complex 1
(left) and (tmeda)CrIIICl3 complex (right). Green: Cr, blue: N,
yellow: Cl. All hydrogen atoms omitted for clarity.
After an extensive trial,
a
single crystal of
(tmeda)SiCH(CrCl2)2 complex 2 suitable for X-ray crystallo-
graphic analysis was obtained by recrystallization from a mix-
ture of THF and hexane. The ORTEP drawing shown in Fig-
ure 2 shows the molecular structure of 2, which has two chro-
mium centers with a TMEDA ligand bridged by a methine
carbon. Selected interatomic distances and angles are listed in
Table 1. The Cr1−C7−Cr1’ bond angle of 89.0° was larger
than that previously reported for the Cr−C−Cr bond angle:
71.8° for CH2[Cp*Cr(-Me)]2, 84.1° for [Cp*Cr(-
CHSiMe3)]2, and 81.7° for MeCH[5-Py’Cr(-Cl)]2 (Py’ =
2,5-di-tert-butylpyrrolide anion).16b,c,f In addition, the Cr1C7
bond distance of 2.082 Ǻ, was longer than that reported for
typical gem-dichromiomethane complexes: 2.033 and 2.050 Ǻ
for CH2(Cp*Cr(-Me))2, 1.993 and 2.017 Ǻ for [Cp*Cr(-
CHSiMe3)]2, and 2.048 Ǻ for MeCH[5-Py’Cr(-Cl)]2.16b,c,f
The current CrC bond distance is even longer than those of
alkylchromium complexes, although none of the gem-
dichromiomethane complexes reported previously possessed
nitrogen ligands and thus are difficult to compare directly.16
The longer CrC bond distance may be attributable to the
trans influence by the strong -donating nature of the diamine
ligand. The two CrN bond distances of 2, which ranged from
2.179 to 2.366 Ǻ, are longer than that of (tmeda)CrCl2 1
(2.149 to 2.187 Ǻ) and (tmeda)CrCl3 (2.165 to 2.198 Ǻ), but
Scheme 2. Reactivity control of gem-dimetallomethanes using
a Lewis acid and base
■ RESULTS AND DISCUSSION
Synthesis and Structure Characterization of gem-
Di(dichlorochromio)methane Complex with TMEDA Lig-
and. Reaction of CrCl2 with TMEDA in THF at 25 °C resulted
in the formation of (tmeda)CrIICl2 complex 1 as a blue precipi-
tate (Scheme 3).14 (tmeda)CrIIICl3 was also prepared as a refer-
ence compound by reaction of CrCl3 with TMEDA in acetoni-
trile at 25 °C (see Supporting Information (SI) for details). The
structures of these complexes were confirmed by X-ray crys-
tallographic analysis (Figure 1, see also Figure S1 and S3 in
SI). The single crystal obtained by slow evaporation of ace-
tonitrile showed chlorine-bridged dimeric structure of 1.
(tmeda)CrCl3 exhibited a square-pyramidal configuration with
an empty site trans to the CrCl bond. A single crystal exhib-
iting a trigonal-bipyramidal geometry was not obtained. Next,
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was observed during silylcyclopropanation after heating at
are in the range typically observed for CrN dative bonds. The
1
100 °C for 30 min. Although a major drawback of the
di(dichlorochromio)methane species used previously was their
instability, no obvious decrease in reactivity toward cyclopro-
panation was observed, even after 6 months, due to stabiliza-
tion by TMEDA, as long as 2 was kept in the solid state under
an argon atmosphere.
bridging chlorides (2.411 to 2.422 Å) have longer CrCl dis-
tances than the terminal chloride (2.307 Å). The CrCl dis-
tances of terminal chlorides of 1 (2.366 to 2.396 Å) were long-
er than those of 2, because the geometry around Cr of 1 was
roughly square planar, and the trans effect exerted by TMEDA
affected it more directly. Although other gem-
di(dichlorochromio)methane complexes having silyl, iodo, and
boryl functionalities on the bridged methine carbons,7 stabi-
lized with various ligands, including pyridine, bipyridine, and
PPh3, could be synthesized in a similar procedure, all attempts
to obtain suitable crystals for single-crystal X-ray crystallo-
graphic analysis by recrystallization failed. These results may
imply that the bulky trimethylsilyl group effectively stabilized
the unstable gem-dichromiomethane species, which was ad-
vantageous for isolation and structural characterization by X-
ray crystallography.
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Scheme 4. Silylcyclopropanation of an olefin with gem-
di(dichlorochromio)methane complex 2
Several main-group metal-based organometallic reagents
having metal-halogen bonds were unstable in the solution state
due to Schlenk equilibrium.17 For example, the gem-
di(iodozincio)methane complexes, R2C(ZnX)2, underwent a
change in chemical structure via Schlenk equilibrium, i.e. self-
transmetallation to produce dimeric, trimeric, and oligomeric
zinc species, as reported previously.4 In contrast, 2 did not
undergo decomposition in THF at 25 °C for 24 h, and the cor-
responding silylcyclopropane 3a was obtained in 88% yield
from reaction with allyl benzyl ether (Scheme 5(a)).18 Because
SiCH(CrCl2)2 species without TMEDA ligand lost reactivity
after being kept in THF for 24 h, TMEDA effectively stabi-
lized the generated gem-dichromiomethane species (Scheme
5(b)).
Figure 2. X-ray crystal structure of the gem-
di(dichlorochromio)methane complex 2. Left: front view;
right: side view. Thermal ellipsoids are drawn at the 50%
probability level. Green: Cr, pink: Si, blue: N, yellow: Cl. All
hydrogen atoms omitted for clarity.
Table 1. Selected interatomic distances and angles for 2.
Reactivity and Stability of gem-Di(dichlorochromio)-
methane Complex with TMEDA. (tmeda)SiCH(CrCl2)2
complex 2 can be utilized as a silylmethylidene carbene equiv-
alent for the cyclopropanation of olefins.9b,c Cyclopropylsilane
3a was obtained in 92% yield (trans / cis = 66 / 34) by treating
2 equiv of 2 with allyl benzyl ether (Scheme 4).12 The results
clearly show that the real reactive species of the chromium-
mediated silylcyclopropanation was a gem-dichromiomethane,
not chromium carbenoid (CrCR2I).9d,e Note that isolation of
several gem-dichromiomethane complexes has been reported
previously;16 however, none were utilized as gem-
dimetallomethane reagents. To obtain further insights into the
reactive nature of 2, its stability in the solid state was exam-
ined utilizing cyclopropanation of allyl benzyl ether as a reac-
tion probe (see Scheme S3 in SI for details). The results indi-
cated that 2 was relatively stable, even in air, but was unstable
toward water. Moreover, the solid sample of 2 was stable,
even at high temperatures, and no notable decrease in yield
Scheme 5. Stability of gem-dichromiomethane species in THF
Effect of Ligands on Silylcyclopropanation of Olefins. The
effect of ligands on silylcyclopropanation was investigated
(Table 2). Without any ligands, the expected 3a was obtained,
albeit in low yield (entry 1). Compared to reaction with
TMEDA, the stereoselectivity was improved to trans / cis = 78
/ 22 with sterically more hindered TEEDA (N,N,N’,N’-
tetraethylethylenediamine) as a ligand (entries 2 and 3).
Monodentate nitrogen ligands, such as triethylamine, DMAP
[(4-dimethylamino)pyridine], and 2,6-lutidine, as well as pyri-
dine-based bidentate ligands, including 2,2’-bipyridyl and
9,10-phenanthrene, nearly shut down the silylcyclopropanation
of allyl benzyl ether (entries 4-8). Although N,N,N’,N’-
tetramethylcyclohexane-1,2-diamine L1 promoted cyclopro-
panation, similar alkylamino group-substituted bidentates L2,
L3, and L4 did not provide the expected 3a (entries 9-12).
Tridentate
ligands,
such
as
N,N,N’,N”,N”-
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pentamethyldiethylenetriamine L5, was also ineffective for the (tmeda)SiCH(CrCl2)2 complex 2 (Scheme 6). Although Fürst-
1
current silylcyclopropanation (entry 13). In contrast, phos-
phine-based ligands, such as triphenylphosphine and 1,2-
diphosphinoethane, gave silylcyclopropane 3a in 26% and
54% yields, respectively (entries 14 and 15). These results
confirm the importance of a TMEDA ligand in silylcyclopro-
panation for reaction efficiency and stereoselectivity. The
trans effect by the strongly -donating TMEDA ligand elon-
gated the carbonchromium bonds of gem-dichromiomethane
complex 2, which was confirmed by the ORTEP drawing
shown in Figure 2 (CrC bond distance of 2.082 Ǻ was longer
than other typical alkylchromium complexes). Because the
elongated CCr bond of TMEDA-ligated 2 can be cleaved
easily, the formation of a chromium reactive species (dinuclear
chromocarbene species 8 in Figure 5) would be favored in the
presence of TMEDA. The coordinately flexibility of TMEDA
ligand compared with L1 and L2 was also advantageous for
promoting the approach of alkenes to the active center of
chromium reactive species.19
ner et al. have addressed this issue, development of catalytic
redox processes based on a ligand-coordinated CrII and CrIII
cycle remain limited.7f,20 Thorough investigation let to the
realization that the inexpensive and less toxic manganese
powder could promote the reduction efficiently. Using 6 equiv
of manganese powder, catalytic silylcyclopropanation of ally
benzyl ether occurred with 10 mol% of 2.12 The yield was
increased when 1 equiv of SiCHI2 and 3 equiv of manganese
were treated at the beginning, and further addition of the re-
maining SiCHI2 and manganese in 8 h at 50 °C (Table 4, entry
1). No cyclopropanation occurred with manganese in the ab-
sence of 2, and 92% of the allyl benzyl ether was recovered
intact (entry 2). Use of the manganese is important, because
cyclopropanation did not proceed using other reductants, in-
cluding magnesium, zinc, iron, or indium.21 Although the ex-
act reason for this is not clear, it might be due to competition
between halogen-metal exchange and the desired generation of
2 in the presence of metals other than manganese. The reaction
was also promoted with catalytic amounts of 1 by using man-
ganese as a reductant (see Table S2 in SI). However, the use of
2 as a catalyst is recommended considering the instability of 1
toward air and moisture, and the difficulty in obtaining 1 in a
pure form.22
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Table 2. Effect of ligands on silylcyclopropanation of alkenes
Scheme 6. Working hypothesis for the mechanism of chromi-
um-catalyzed silylcyclopropanation of olefins
The generality of catalytic silylcyclopropanation using 2 as
a catalyst was investigated briefly. The stereoselectivity was
improved in reaction of allylbenzylamine having coordinating
functionality to furnish the corresponding cyclopropane 3b in
74% yield (trans / cis = 80 / 20) (Table 3, entry 3). Arylolefins
as well as alkylolefins were applicable for the current cyclo-
propanation (entry 4). Myrcene reacted selectively at the ter-
minal double bond to afford the corresponding 3d in 58%
yield (entry 5). This terminal selective cyclopropanation can-
not be achieved by traditional Simmons-Smith reaction, in
which di- and trisubstituted double bonds react preferentially
over monosubstituted alkenes.23
Mechanistic Investigation of Silylcyclopropanation of Ole-
fins. As shown in Scheme 1, the unique change in reactivity of
2 occurred upon addition of TMEDA in the current study. The
gem-dichromiomethane species, SiCH(CrCl2)2, itself prefers
polar carbonheteroatom double bonds of aldehydes, while
the TMEDA-ligated species reacted with relatively non-polar
carboncarbon double bonds of alkenes to provide cyclopro-
pane derivatives. Similar reactivity control of gem-
dimetallomethane has been reported by Grubbs and coworkers,
involving dissociation of the Tebbe reagent from titanacarbene
species and Me2AlCl, promoted by 4-(dimethylamino)pyridine
(DMAP) (Scheme 7).13 While the Tebbe reagent promoted the
methylenation of aldehydes, the titanacarbene species was
reported to promote the polymerization of olefins by the me-
Catalytic Cyclopropanation of Alkenes with gem-
Di(dichlorochromio)methane Complexes. As shown in
Scheme 3, 2 equiv of (tmeda)CrIIICl2I was formed as a by-
product via two consecutive single-electron transfers of
(tmeda)CrIICl2 1 to (diiodomethyl)trimethylsilane (SiCHI2)
during the generation of (tmeda)SiCH(CrCl2)2 complex 2.
Given the reduction of (tmeda)CrIIICl2I back to 1, the reaction
would proceed even with
a
catalytic amount of
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tathesis mechanism via the formation of titanacyclobutane cussed initial rate of cyclopropanation was determined exclud-
1
intermediates.
ing the data of the induction period.
2
3
Table 3. Catalytic silylcyclopropanation of olefins with 2a
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Figure 3. Kinetic expression of the rate for formation of 3a
with chromocarbene species 2’
Scheme 7. Generation of titanacarbene species from Tebbe
reagent and their reactivity, as reported by Grubbs et al.13
Based on the Grubbs’s report, the generation of mononucle-
ar chromocarbene complex 2’ was hypothesized to be promot-
ed by the TMEDA ligand in the presence of olefins, and the
formation of chromocyclobutanes with alkenes thought to
occur in the current silylcyclopropanation. Since the reaction
was promoted by mononuclear 2’, the rate for the formation of
3a (d[3a]/dt) can be expressed by the equation shown in Fig-
ure 3. Here, “K” is the equilibrium constant for the dissocia-
tion of 2 to 2’ and (tmeda)CrCl3 7, and “k” is the rate constant
for the cyclopropanation. The rate expression could be reduced
by the approximation of “[2’] = [7]”. Based on this expression,
inverse first-order dependence on the concentration of 2 was
expected initially. However, this rate expression was not con-
sistent with the experimental data obtained from cyclopropa-
nation kinetics. A roughly linear relationship between yield of
3a and time was observed during the initial stage of the reac-
tion (Figure 4(a)), and the initial rate of cyclopropanation was
first-order-dependent on the amount of 2 (Figure 4(b)). These
results indicate that reaction with ally benzyl ether was pro-
moted by the dinuclear chromium species without dissociation
to mononuclear chromocarbene species 2’. Note that an induc-
tion period and sigmoidal reaction profile were observed in the
early stage of reaction when catalyst loading was less than 30
mol%. This is consistent with the in-situ formation of the reac-
tive dinuclear chromocarbene species from 2, and above dis-
Figure 4. (a) Reaction profile for cyclopropanation of allyl
benzyl ether in THF at 50 °C with 20 mol% (●), 30 mol%
(■), 40 mol% (▲), and 50 mol% (×) of 2. (b) Plot of initial
rate for the formation of 3a vs concentration of 2.
The reaction mechanism for cyclopropanation is proposed
as shown in Figure 5, in which the chlorine-bridged dinuclear
chromium complex acts as a catalytic active species based on
the kinetic study. First, (diiodomethyl)trimethyl silane
(SiCHI2) is reduced by 4 equiv of (tmeda)CrCl2 1 to form
(tmeda)SiCH(CrCl2)2 complex 2 along with 2 equiv of
(tmeda)CrCl2I. The (tmeda)CrCl2I is reduced back to catalyti-
cally active species 1 by manganese powder. Based on the
Grubbs’s report in Scheme 7,13 the resulting 2 is converted
into chromocarbene species 8 in the presence of TMEDA and
olefins, which then forms chromocyclobutane intermediate 9
via [2+2]cycloaddition with olefins. Here, coordination to
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another chromium center promotes the approach of olefins to Table 4. Effect of a Lewis acid on silylalkylidenation of an
1
2
3
4
5
6
7
8
chromocarbene moiety. Only the terminal double bond of ole-
fins can to participate in the catalytic cycle due to the steric
hindrance around the chromium center; the trimethylsilyl
group prefers to locate opposite of the substituent on alkenes
in intermediate 8, which can explain the chemo- and stereose-
lectivity observed in Table 3, i.e. trans-silylcyclopropanes
were formed as major products, and the terminal double bond
of myrcene reacted selectively. Finally, reductive elimination
from chromocyclobutane 9 afforded silylcyclopropane 3 along
with regeneration of active catalytic species 1.
aldehyde with gem-di(dichlorochromio)methane complex 2
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which was further supported by precipitation of (tmeda)ZnCl2
as colorless crystals (Figure 6(b) and Figure S5 in SI). The
efficiency of ligand exchange from TMEDA to N,N,N’,N’-
tetramethyl-1,3-propanediamine was estimated by comparing
the yields of cyclopropanation. The corresponding cyclopro-
pane 3a was obtained in 56% yield with a trans / cis = 80 / 20
after ligand exchange to N,N,N’,N’-tetramethyl-1,3-
propanediamine. The yield and stereoselectivity were similar
to those obtained with gem-dichromiomethane complex 6
(51% yield with trans / cis = 77 / 23), which indicated that the
removal of TMEDA occurred almost quantitatively (see
Scheme S1 and S2 in SI for comparison studies).
Figure 5. Proposed reaction mechanism for chromium-
catalyzed silylcyclopropanation
Reactivity Control of gem-Di(dichlorochromio)methane
Complex upon Treatment with ZnCl2. A previous our study
revealed that alkylidenation of aldehydes occurred with func-
tionalized diiodomethane derivatives and CrCl2.6 However,
(tmeda)SiCH(CrCl2)2 complex 2 was inert toward silylalkyli-
denation, and the corresponding alkenylsilanes were not ob-
tained from reaction with 3-phenylpropanal in THF. However,
it was found that treatment of 2 with ZnCl2 prior to addition of
the aldehyde altered the reaction course to furnish the corre-
sponding alkenylsilane 4a in 74% yield (E / Z = >99 / 1) (Ta-
ble 4, entry 6). At first, ZnCl2 was thought to activate 3-
phenylpropanal as a Lewis acid to promote the nucleophilic
attack of a gem-di(dichlorochromio)methane reagent. Howev-
er, a similar acceleration effect of ZnCl2 was not observed in
the silylalkylidenation using CrCl2 without TMEDA in THF
(Table S1 in SI). Other metal salts, such as ZnBr2 and ZnI2,
also promoted the reaction (entries 7 and 8), whereas TiCl4,
MnCl2, FeCl3, CoCl2, and CuI were not effective, and 4a was
formed in significantly lower yield, probably due to competi-
tive decomposition of the aldehyde via aldol condensation
leading to 5 (entries 1-5). Although characterization of the
reactive species upon addition of ZnCl2 was attempted, obtain-
ing information directly was difficult due to the instability of
the resulting chromium complexes. After an extensive trial,
the corresponding gem-dichromiomethane complex 6 stabi-
lized with N,N,N’,N’-tetramethyl-1,3-propanediamine ligand
was obtained from reaction of 2 with subsequent treatment of
ZnCl2 followed by N,N,N’,N’-tetramethyl-1,3-propanediamine
(Scheme 8). The red single crystal of 6 was obtained by slow
diffusion of its THF solution, and its structure was determined
unambiguously by single-crystal X-ray crystallography (Fig-
ure 6(a), see also Figure S4 in SI). These results clearly sug-
gest that the TMEDA ligand of 2 was removed by ZnCl2,
Scheme 8. Removal and exchange of TMEDA ligand of gem-
di(dichlorochromio)methane complex 2
Figure 6. X-ray crystal structure of the gem-
dichromiummethane complex 6 stabilized with N,N,N’,N’-
tetramethyl-1,3-propanediamine (left) and (tmeda)ZnCl2 com-
plex (right). Green: Cr, pink: Si, blue: N, yellow: Cl, red: Zn,
respectively. All hydrogen atoms are omitted for clarity.
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The (tmeda)SiCH(CrCl2)2 complex 2 could also be utilized
Table 6. Effect of ligand on silylalkylidenation of aldehydes
1
2
3
4
5
6
7
8
as a catalyst for silylalkylidenation of aldehydes by pretreat-
ment with ZnCl2. 3-Phenylpropanal was converted to 4a in a
similar yield compared to that obtained from the stoichio-
metric silylalkylidenation shown in Table 4, entry 6 (Table 5,
entry 1). Reaction with sterically congested 2-phenylpropanal
provided 4b in 74% yield with excellent stereoselectivity (en-
try 2). The bromide group in 4c, which can be further used in
cross-coupling reactions, was tolerated under the current con-
ditions (entry 3). Ethoxycarbonyl and ethynyl groups remained
intact to provide 1,6-enyne 4d, which was applicable as a pre-
cursor for further cycloaddition reactions (entry 4).24 These
results demonstrated the potential utility of the present chro-
mium-catalyzed transformation in various organic syntheses.25
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Table 5. Catalytic silylalkylidenation of aldehydes with 2a
direct X-ray crystallographic characterization of reactive gem-
dichromiomethane complexes. The isolated gem-dichromio-
methane complex can serve as a silylmethylidene carbene
equivalent for cyclopropanation of olefins, which is capable of
being stored in the solid state without degradation for at least
half a year. Furthermore, this complex itself preferred the non-
polar carboncarbon double bond of alkenes to provide cyclo-
propane derivatives, while pretreatment with ZnCl2 changed
the reactive nature of the complex, resulting in alkylidenation
with polar aldehydes. Similar reactivity control upon addition
of a Lewis acid (ZnCl2) or a Lewis base (TMEDA) is rare for
gem-dimetalloalkanes.13 The catalytic performance of gem-
dichromiomethane complexes in both alkylidenation and cy-
clopropanation was also disclosed. Although the scope and
limitations of the reactions over a range of aldehydes and ole-
fins have not been demonstrated, we believe the current pre-
liminary results sufficiently prove the usefulness of the present
new findings. A kinetic study of the silylcyclopropanation
clarified the role of TMEDA, and provided insight into the
unique reaction mechanism with a chlorine-bridged dinuclear
chromium complex. The steric effect of a chromocarbene in-
termediate led to selective cyclopropanation of the terminal
double bond of myrcene. This terminal selectivity is unique
because di- and trisubstituted alkenes preferentially react in a
traditional Simmons-Smith cyclopropanation.23,26 Overall, the
current work provides invaluable information for the design of
efficient and storable organochromium reagents.1 Application
of the strategy for the preparation of novel early transition
metal-based gem-dimetalloalkanes is ongoing in our laborato-
ry.
Impact of TMEDA and ZnCl2 on Control of Reactivity of
gem-Dichromiomethane Complexes. To confirm the im-
portance of the combination of TMEDA and ZnCl2 on reac-
tivity control of gem-dichromiomethane species, the behavior
of other gem-(dichromio)silylmethane species having different
ligands was investigated upon addition of ZnCl2 (Table 6).
The most drastic reactivity change upon addition of ZnCl2 was
observed for the gem-dichromiomethane complex having the
TMEDA ligand (entry 1). Although other gem-
dichromiomethane complexes coordinated by nitrogen- and
phosphine-based ligands also promoted the silylalkylidenation
of 3-phenylpropanal with the pretreatment of ZnCl2, none of
them gave 4a in superior yield (entries 2-8). This difference in
yields may be a result of the efficiency of ligand dissociation
from the chromium center. TMEDA gave the best result due to
the high stability of the resulting (tmeda)ZnCl2 complex,
which prevented rebound of TMEDA to ligand-free gem-
dichromiomethane species. These results imply that the proper
choice of ligands is key for the control of reactivity to attain
both silylcyclopropanation and silylalkylidenation.
EXPERIMENTAL SECTION
Synthesis of (tmeda)SiCH(CrCl2)2 Complex 2. A flame-dried
two-necked round bottom flask was charged with CrCl2 (197 mg,
1.6 mmol) and THF (4.0 mL), and TMEDA (196 mg, 1.6 mmol)
was added dropwise at 25 °C. After stirring for 20 min, (diiodo-
methyl)trimethylsilane (136 mg, 0.40 mmol) was added, and the
resulting mixture was stirred at 25 °C for 1 h. The reaction mix-
■ CONCLUSIONS
Covering the reactive methylene center with a bulky trime-
thylsilyl group and TMEDA ligand led to the isolation and
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ture was passed through a cotton plug under an argon atmosphere,
REFERENCES
1
2
3
4
5
6
7
8
and the filtrate was concentrated under reduced pressure. The
resulting solid was extracted with CH2Cl2 / hexane (v / v = 3 / 2)
several times, and the solvent was removed under reduced pres-
sure to afford (tmeda)SiCH(CrCl2)2 complex 2 (128 mg, 0.23
mmol, 57% yield) as a red solid. 1H NMR and 13C NMR were not
applicable due to the paramagnetic nature of chromium com-
pounds. However, the structure was unambiguously determined
by the X-ray single crystallographic analysis of a red crystal of 3,
obtained by recrystallization from THF. IR (KBr / cm-1): 3364,
2976, 2889, 2843, 2641, 1473, 1441, 1283, 1240, 1121, 1065,
1016, 955, 853, 799, 770. Anal. Calc. for C16H42Cl4Cr2N4 Si: C,
34.05; H, 7.50; N, 9.93. Found: C, 33.71; H, 7.21; N, 9.54.
1. Representative reviews, see: (a) Marek, I.; Normant, J.-F. Chem. Rev.
1996, 96, 3241. (b) Matsubara, S.; Oshima, K.; Utimoto, K. J. Organ-
omet. Chem. 2001, 617-618, 39. (c) Marek, I.; Normant, J. F. In Or-
ganozinc Reagents-A Practical Approach; Knochel, P., Jones, P., Eds.;
Oxford University Press: Oxford, 1999; pp 119-137. (d) Normant, J. F.
Acc. Chem. Res. 2001, 34, 640. (e) Endo, K. Bull. Chem. Soc. Jpn. 2017,
90, 649.
2. (a) Tebbe, F. N.; Parshall, G. W.; Reddy, G. S. J. Am. Chem. Soc. 1978,
100, 3611. For reviews on the methylenation of carbonyl compounds,
see: (b) Matsubara, S.; Oshima, K. In Modern Carbonyl Olefination;
Takeda, T. Ed.; Wiley-VCH: Weinheim, 2004; pp 200.
3. X-ray crystallographic studies on gem-dimetallomethanes containing ,
see: (a) Hogenbirk, M.; Schat, G.; Akkerman, O. S.; Bickelhaupt. F. J.
Am. Chem. Soc. 1992, 114, 7302. (b) Vestergren, M.; Eriksson, J.;
Hakansson, M. J. Organomet. Chem. 2003, 681, 215. (c) Layfield, R.
A.; Bullock, T. H.; Garcia, F.; Humphrey, S. M.; Schuler, P. Chem.
Commun. 2006, 2039. (d) Uhl, W.; Layh, M. J. Organomet. Chem. 1991.
415. 181. (e) Stasch, A.; Ferbinteanu, M.; Prust, J.; Zheng, W.; Cim-
poesu, F.; Roesky, H. W.; Magull, J.; Schmidt, H.-G.; Noltemeyer, M. J.
Am. Chem. Soc. 2002, 124, 5441. (f) Stasch, A.; Roesky, H. W.; Vidov-
ic, D.; Magull, J.; Schmidt, H.-G.; Noltemeyer, M. Inorg. Chem. 2004,
43, 3625.
9
10
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12
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16
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18
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20
21
22
23
24
25
26
27
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29
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33
34
35
36
37
38
39
40
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48
49
50
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General Procedure for Chromium-Catalyzed Silylcyclopro-
panation of Alkenes (Table 3). To
a suspension of
(tmeda)SiCH(CrCl2)2 complex 2 (11.3 mg, 0.020 mmol for 3a and
3b, or 22.6 mg, 0.040 mmol for 3c and 3d) in THF (2.0 mL for 3a,
3c, and 3d, or 1.0 mL for 3b) was added (diiodome-
thyl)trimethylsilane (68.0 mg, 0.20 mmol), an olefin (0.20 mmol),
and manganese powder (33.0 mg, 0.60 mmol), followed by stir-
ring at 50 oC for 8 h. (Diiodomethyl)trimethylsilane (68.0 mg,
0.20 mmol) and manganese powder (33.0 mg, 0.60 mmol) were
4. Nishida, Y.; Hosokawa, N.; Murai, M.; Takai, K. J. Am. Chem. Soc.
2015, 137, 114.
o
5. For reviews on chromium-promoted reactions, see: (a) Hodgson, D. M.
J. Organomet. Chem. 1994, 476, 1. (b) Fürstner, A. Chem. Rev. 1999, 99,
991. (c) Wessjohann, L. A.; Scheid, G. Synthesis 1999, 1. (d) Takai, K.
Org. React. 2004, 64, 253. (e) Smith, K. M. Coord. Chem. Rev. 2006,
250, 1023. (f) Yamamoto, H.; Xia, G. Chem. Lett. 2007, 36, 1082. For
oligo- and polymerization, see: (g) Wass, D. F. Dalton Trans. 2007, 8,
816. (h) Smith, K. M. Curr. Org. Chem. 2006, 10, 955. (i) Takai, K. In
Comprehensive Organic Synthesis, 2nd ed.; Molander, G. A.; Knochel, P.
Eds. Elsevier, Oxford, 2014, 1, 159-203. For recent reports, see: (j) Steib,
A. K.; Kuzmina, O. M.; Fernandez, S.; Flubacher, D.; Knochel, P. J. Am.
Chem. Soc. 2013, 135, 15346. (k) Zeng, X.; Cong, X. Org. Chem. Front.
2015, 2, 69, and references therein.
6. For pioneering works on the generation and utilization of gem-
dichromiomethane species for alkylidenation of aldehydes, see: (a)
Takai, K.; Nitta, K.; Utimoto, K. J. Am. Chem. Soc. 1986, 108, 7408. (b)
Okazoe, T.; Takai, K.; Utimoto, K. J. Am. Chem. Soc. 1987, 109, 951.
7. For chromium-mediated silyl-, boryl-, stannyl-, and iodoalkylidenation,
see: (a) Takai, K.; Kataoka, Y.; Okazoe, T. Utimoto, K. Tetrahedron
Lett. 1987, 28, 1443. (b) Hodgson, D. M. Tetrahedron Lett. 1992, 33,
5603. (c) Hodgson, D. M.; Foley, A. M.; Lovell, P. J. Tetrahedron. Lett.
1998, 39, 6419. (d) Takai, K.; Ichiguchi, T.; Hikasa, S. Synlett 1999,
1268. (e) Takai, K.; Hikasa, S.; Ichiguchi, T.; Sumino, N. Synlett 1999,
1769. For catalytic version of reaction, see: (f) Takai, K.; Kunisada, Y.;
Tachibana, Y.; Yamaji, N.; Nakatani, E. Bull. Chem. Soc. Jpn. 2004, 77,
1581. For alkylidenation of aldehydes leading to acrylate derivatives,
see: (g) Falck, J. R.; Bejot, R.; Barma, D. K.; Bandyopadhyay, A.; Jo-
seph, S.; Mioskowski, C. J. Org. Chem. 2006, 71, 8178. (h) Baati, R.;
Mioskowski, C.; Kashinath, D.; Kodepelly, S.; Lu, B.; Falck, J. R. Tet-
rahedron Lett. 2009, 50, 402.
8. For selected examples, see: (a) Evans, D. A.; Black, W. C. J. Am. Chem.
Soc. 1993, 115, 4497. (b) Wender, P. A.; Schrier, A. J. J. Am. Chem.
Soc. 2011, 133, 9228. (c) Dieckmann, M.; Kretschmer, M.; Li, P.; Ru-
dolph, S.; Herkommer, D.; Menche, D. Angew. Chem. Int. Ed. 2012, 51,
5667. (d) Willwacher, J.; Fürstner, A . Angew. Chem. Int. Ed. 2014, 53,
4217. (e) Tsuzaki, S.; Usui, S.; Oishi, H.; Yasushima, D.; Fukuyasu, T.;
Oishi, T.; Sato, T.; Chida, N. Org. Lett. 2015, 17, 1704.
9. (a) Takai, K.; Toshikawa, S.; Inoue, A.; Kokumai, R. J. Am. Chem. Soc.
2003, 125, 12990. (b) Takai, K.; Hirano, M.; Toshikawa, S. Synlett 2004,
1347. (c) Takai, K.; Toshikawa, S.; Inoue, A.; Kokumai, R.; Hirano, M.
J. Organomet. Chem. 2007, 692, 520. Utilizing our pioneering study,
Concellón et al. reported chromium-mediated cyclopropanation of ,-
unsaturated amides. Chromium carbenoids (Cl2CrCR2X) is proposed
as intermediates in their reports. See: (d) Concellón, J. M.; Rodríguez-
Solla, H.; Méjica, C.; Blanco, E. G. Org. Lett. 2007, 9, 2981. (e) Con-
cellón, J. M.; Rodríguez-Solla, H.; Méjica, C.; Blanco, E. G.; García-
Granda, S.; Díaz, M. R. Org. Lett. 2008, 10, 349.
added and stirred at 50 C for an additional 16 h. The reaction
mixture was poured into water (10 mL), followed by extraction
with Et2O (10 mL) three times. The combined organic extracts
were dried over anhydrous MgSO4, filtered, and the solvent was
removed under reduced pressure. The residue was purified by
flash column chromatography on silica gel to afford the corre-
sponding cyclopropane derivatives 3.
ASSOCIATED CONTENT
Supporting Information
The Supporting Information is available free of charge via the
Internet at http://pubs.acs.org. Experimental procedures, charac-
terization data, and X-ray crystallographic data for complex 1, 2,
6, (tmeda)CrCl3, and (tmeda)ZnCl2.
AUTHOR INFORMATION
Corresponding Author
masahito.murai@okayama-u.ac.jp
ktakai@cc.okayama-u.ac.jp
ORCID
Masahito Murai: 0000-0002-9694-123X
Kazuhiko Takai: 0000-0002-2572-0851
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
This work was financially supported by a Grant-in-Aid (No.
26248030) from MEXT, Japan. The authors gratefully thank Dr.
Hiromi Ota and Dr. Sobi Asako (Okayama University) for the
valuable discussion, and Mr. Masato Kodera and Ms. Seina Ishi-
hara (Okayama University) for HRMS measurements. The au-
thors gratefully thank Division of Instrumental Analysis, Okaya-
ma University for the X-ray single crystal structural analyses.
10. For reviews on the synthesis of cyclopropanes, see: (a) Lebel, H.;
Marcoux, J.-F.; Molinaro, C.; Charette, A. B. Chem. Rev. 2003, 103,
977. (b) Pellissier, H. Tetrahedron 2008, 64, 7041.
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11. For representative pioneering works, see: (a) Simmons, H. E.; Smith,
61, 321. (h) Tang, P.; Qin, Y. Sythesis 2012, 44, 2969. (i) Chen, D. Y.-
K.; Pouwer, R. H.; Richard, J.-A. Chem. Soc. Rev. 2012, 41, 4631.
R. D. J. Am. Chem. Soc. 1958, 80, 5323. (b) Simmons, H. E.; Smith, R.
D. J. Am. Chem. Soc. 1959, 81, 4256. (c) Furukawa, J.; Kawabata, N.;
Nishimura, J. Tetrahedron Lett. 1966, 7, 3353.
1
2
3
4
5
6
7
8
9
12. Silylcyclopropanes are useful synthetic building blocks. For the syn-
thesis and transformation of silylcyclopropanes, see: (a) Paquette, L. A.
Chem. Rev. 1976, 86, 733. (b) Mata, S.; López, L. A.; Vicente, R. Syn-
lett 2015, 26, 2685, and the references therein.
13. (a) Straus, D. A.; Grubbs, R. H. Organometallics 1982, 1, 1658. (b)
Meinhart, J. D.; Anslyn, E. V.; Grubbs, R. H. Organometallics 1989, 8,
583. For a review, see: c) Beckhaus, R. Angew. Chem. Int. Ed. Engl.
1997, 36, 686.
14. Bachmann, B.; Heck, J.; Massa, W.; Pebler, J. Z. Anorg. Allg. Chem.
1995, 621, 2061.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
15. For the synthesis of (diiodomethyl)trialkylsilanes SiCHI2, see: (a)
Matsubara, S.; Otake, Y.; Morikawa, T.; Utimoto, K. Synlett 1998, 1315.
(b) Bull, J. A.; Charette, A. B. J. Org. Chem. 2008, 73, 8097. (c) Lim, D.
S. W.; Anderson, E. A. Org. Lett. 2011, 13, 4806. See also ref 7f.
16. Isolation and structural characterization of gem-dichromium complex-
es have been reported. All of them possess 5-Cp, Cp* or pyrrolide ani-
on ligands, and were not used as gem-dimetallomethane reagents. See:
(a) Kӧhler, F. H.; Krüger, C.; Zeh, H. J. Organomet. Chem. 1990, 386,
C13. (b) Noh, S. K.; Heintz, R. A.; Janiak, C.; Sendlinger, S. C.; Theo-
pold, K. H. Angew. Chem. Int. Ed. Engl. 1990, 29, 775. (c) Heintz, R.
A.; Leelasubcharoen, S.; Liable-Sands, L. M.; Rheingold, A. L.; Theo-
pold, K. H. Organometallics 1998, 17, 5477. (d) Wei, P.; Stephan, D. W.
Organometallics 2003, 22, 1712. (e) Vidyaratne, I.; Nikiforov, G. B.;
Gorelsky, S. I.; Gambarotta, S.; Duchateau, R.; Korobkov, I. Angew.
Chem. Int. Ed. 2009, 48, 6552. (f) Licciulli, S.; Albahily, K.; Fomitche-
va, V.; Korobkov, I.; Gambarotta, S.; Duchateau, R. Angew. Chem. Int.
Ed. 2011, 50, 2346.
17. (a) Schlenk, W.; Schlenk, W. Ber. Dtsch. Chem. Ges. 1929, 62, 920.
(b) Hirai, A.; Nakamura, M.; Nakamura, E. J. Am. Chem. Soc. 1999,
121, 8665. (c) Goldsmith, P. J.; Teat, S. J.; Woodward, S. Angew. Chem.
Int. Ed. 2005, 44, 2235. (d) Blake, A. J.; Shannon, J.; Stephens, J. C.;
Woodward, S. Chem. Eur. J. 2007, 13, 2462.
18. Yield of 4a in Scheme 3 decreased to 32% (trans / cis = 66 / 34) with
42% recovery of allyl benzyl ether.
19. Under the condition shown in Table 2, regioselectivity of silylcyclo-
propanation was improved to trans / cis = 83 / 17 when (diiodome-
thyl)triisopropyl silane and TMEDA were used as a precursor and a lig-
and, respectively, although yield decreased to 27%.
20. (a) Hu, C.-M.; Chen, J. J. Chem. Soc., Chem. Commun. 1993, 72. (b)
Fürstner, A.; Shi, N. J. Am. Chem. Soc. 1996, 118, 2533. (c) Fürstner,
A.; Shi, N. J. Am. Chem. Soc. 1996, 118, 12349.
21. Addition of MnCl2, which could accumulate during the catalytic pro-
cess, did not promote the reaction.
22. The solubility and stability of (tmeda)CrIICl2 1 were much lower than
those of (tmeda)SiCH(CrIIICl2)2 2. Furthermore, recrystallization by
slow evaporation of an acetonitrile solution was required to obtain 1 in
pure form because of its low solubility in other typical organic solvents,
including MeOH, THF, EtOAc, Et2O, acetone, CH2Cl2, and toluene.
However, even a small amount of acetonitrile strongly inhibited the si-
lylcyclopropanation of alkenes. Thus, 2 was used as a robust and stora-
ble catalyst and promoter in the current work.
23. Due to electronic and steric effects, the reactivity of alkenes in the
Simmons-Smith reaction is known to diminish in the order gem-
disubstituted > trisubstituted > tetrasubstituted > cis-disubstituted >
trans-disubstituted > monosubstituted alkenes.
24. (a) Trost, B. M.; Pfrengle, W.; Urabe, H.; Dumas, J. J. Am. Chem. Soc.
1992, 114, 1923. (b) Trost, B. M.; Hashmi, A. S. K. J. Am. Chem. Soc.
1994, 116, 2183. (c) Asao, N.; Shimada, T.; Yamamoto, Y. J. Am. Chem.
Soc. 1999, 121, 3797.
25. The corresponding alkenylsilane was obtained from the catalytic
alkylidenation of 4-dimethylaminobenzaldehyde in 43% yield (trans /
cis = >99 / 1) under the reaction condition shown in Table 5. However,
the similar catalytic alkylidenation of 4-nitro- and 4-
cyanobenzaldehydes did not proceed at all, which indicates that strongly
coordinating functional groups retard the current alkylidenation.
26. For the utility of cyclopropane derivatives, see: (a) de Meijere, A.;
Kozhushkov, S. I. Chem. Rev. 2000, 100, 93. (b) Salaün, J. Top. Curr.
Chem. 2000, 207, 1. (c) Donaldson, W. A. Tetrahedron 2001, 57, 8589.
(d) Faust, R. Angew. Chem. Int. Ed. 2001, 40, 2251. (e) Gnad, F.; Reiser,
O. Chem. Rev. 2003, 103, 1603. (f) Reissig, H.-U.; Zimmer, R. Chem.
Rev. 2003, 103, 1151. (g) Yu, M.; Pagenkopf, B. L. Tetrahedron 2005,
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