Optimization of Catalyst Structure for Asymmetric Propargylation of Aldehydes with Allenyltrichlorosilane

Article abstract of DOI:10.1002/adsc.202000936

The design of catalysts for asymmetric propargylations remains a challenging task, with only a handful of methods providing access to enantioenriched homopropargylic alcohols. In this work, guided by previously reported computational predictions, a set of

Full text of DOI:10.1002/adsc.202000936

Title: Optimization of Catalyst Structure for Asymmetric Propargylation
of Aldehydes with Allenyltrichlorosilane
Authors: Vladimir Vaganov, Yasuaki Fukazawa, Nikolay Kondratyev,
Sergei Shipilovskikh, Steven Wheeler, Aleksandr Rubtsov,
and Andrei V. Malkov
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To be cited as: Adv. Synth. Catal. 10.1002/adsc.202000936
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10.1002/adsc.202000936
Advanced Synthesis & Catalysis
FULL PAPER
DOI: 10.1002/adsc.202((will be filled in by the editorial staff))
Optimization of Catalyst Structure for Asymmetric
Propargylation of Aldehydes with Allenyltrichlorosilane
Vladimir Yu. Vaganov,a Yasuaki Fukazawa,b Nikolay S. Kondratyev,b Sergei A.
Shipilovskikh,ab Steven E. Wheeler,c Aleksandr E. Rubtsov,a* and Andrei V. Malkovb*
a
Department of Chemistry, Perm State University, Bukireva 15, Perm 614990, Russia. E-mail:rubtsov@psu.ru
Department of Chemistry, Loughborough University, Loughborough, LE11 3TU, UK. E-mail: A.Malkov@lboro.ac.uk
Department of Chemistry, University of Georgia, Athens, GA, USA.
b
c
Received: ((will be filled in by the editorial staff))
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201######.
Abstract. The design of catalysts for asymmetric The reaction scope includes a wide range of aromatic,
propargylations remains a challenging task, with only a heteroaromatic, and unsaturated aldehydes. New
handful of methods providing access to enantioenriched computations confirm that the key stereodetermining
homopropargylic alcohols. In this work, guided by transition state structures for the synthesized catalysts are
previously reported computational predictions, a set of similar to those previously reported for the model structure.
atropisomeric bipyridine N,N’-dioxides was tested as Lewis
base catalysts for the asymmetric propargylation of
aldehydes with trichloroallenylsilane. The catalysts are
easily prepared in four simple steps starting from readily
available methyl ketones. Aryl-substituted derivatives
proved to be highly active and showed a high level of
enantiocontrol even at 1 mol% loading.
Keywords: asymmetric catalysis, enantioselectivity,
propargylation, Lewis bases, atropisomerism
addition[6] with a few examples of chiral catalysis.[7]
With the advent of asymmetric Lewis base
catalysis,[8] the propargylation of aldehydes 1 using
allenyltrichlorosilane 2[9] started to attract the
attention of researchers (Scheme 1); however, it
proved considerably more challenging than the
related allylation, which is reflected in just a handful
of published reports on this transformation.
For instance, Nakajima’s biquinoline N,N’-dioxide
4 (20 mol% loading) afforded homopropargylic
alcohols 3 with modest enantioselectivity (≤ 52%
ee),[10] in contrast to the results attained in the
respective allylation (≤ 92% ee).[11] On the other hand,
highly enantioselective formation of 3 (≤ 96% ee) has
been reported for the helical pyridine N-oxide 5 as
catalyst (at 10 mol% loading).[12] Several
computational studies were carried out to address the
apparent disparity in the enantioselectivities seen in
the allylation and propargylation of aldehydes
catalyzed by bipyridine N-oxides or N,N’-dioxides
and also to gain a deeper insight into the mechanism
Introduction
The asymmetric nucleophilic propargylation of
aldehydes is a convenient method for the formation
of C-C bonds that introduces an unsaturated fragment
into the molecule. While representing
a
complementary methodology to the widely used
allylation reaction, the propargylation reaction stays
in the shadow of its more established counterpart
despite the fact that the resultant homopropargylic
alcohols serve as versatile synthetic building
blocks.[1] Typically, the protocols involve addition of
preformed or made in situ organometallic
propargylating reagents to carbonyl compounds in the
presence of a catalyst. Recently, alternative methods
emerged employing 1,3-enynes as allenylmetal
equivalents in transition metal mediated asymmetric
propargylation.[2]
Transition
metal-free
methodologies for asymmetric propargylations of
carbonyl compounds mostly revolve around
organoboron and organosilicon reagents, the former
being more actively exploited.[3] Thus, boron reagents
have been successfully employed in the catalytic
asymmetric propargylation of both aldehydes[4] and
ketones.[5] Asymmetric synthesis employing the
respective silicon reagents, alongside their tin
counterparts, in the past was mostly focused on the
use of enantioenriched chiral derivatives where a
non-chiral catalyst was used to facilitate the
of
stereodifferentiation in the
For example,
asymmetric
the high
propargylation.[13]
enantioselectivity attained with 5 resulted, in part,
from the through-space electrostatic interactions of
the formyl C-H with the Cl ligands on Si, rather than
noncovalent aryl−aryl interactions between the
aromatic aldehyde and the catalyst.[13b] Wheeler and
co-workers
computational
subsequently
developed
the
toolkit AARON
(Automated
1
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10.1002/adsc.202000936
Advanced Synthesis & Catalysis
Alkylation Reaction Optimizer for N-oxides), which
enabled virtual screening of various bipyridine N,N’-
dioxides scaffolds for designing highly selective
catalysts for the asymmetric propargylation of
aldehydes.
synthesized in pure diastereomeric forms.
Furthermore, as shown below computationally, the
transition state (TS) structures for 7 are nearly
identical to the corresponding substituted form of 6.
Scheme 2. Synthesis of atropisomeric bipyridine N,N’-
dioxides 7.
A set of compounds employed in this work,
including derivatives with the substitution pattern
identified as optimal in the theoretical studies by
Wheeler,[14b] is presented in Scheme 2. Catalyst
performance was assessed in a model addition of
allenylsilane 2 to benzaldehyde using 10 mol%
catalysts loading at –60ºC for 18 h. The results are
presented in Table 1.
Scheme 1. Asymmetric propargylation of aldehydes
catalyzed by pyridine N-oxides.
Axially chiral N,N’-dioxides 6 were identified as
promising candidates (Scheme 1) where certain
derivatives were predicted to show high
enantioselectivity.[14] However, it is important to
mention that these computational predictions only
considered selectivity and did not take into account
catalytic activity, adding further need for
experimental verification of the proposed structures.
Herein, we present a practical assessment of close
analogues of the theoretically proposed catalyst
structures in asymmetric propargylation of aldehydes
Table 1. Catalyst screening in addition of
trichloroallenylsilane 2 to benzaldehyde 1a.a
with
allenyltrichlorosilane,
leading
to
the
identification of a novel, highly efficient catalytic
system.
entry catalyst 7, R
conversion,
ee,
b
%
(%)c
1
2
3
4
5
6
7
8
7a, (Sa)-Ph
7a, (Ra)-Ph
7b, CF3
7c, CN
7d, tBu
7e, 3,5-(CF3)2C6H3
7f, 4-ClC6H4
7g, 4-MeOC6H4
7h, 2-Naphthyl
7i, 2-Furyl
99
99
trace
≤5
≤5
99
99
70
99
60
99
96
96d
n.d.
69
50
93
97
93
95
60
76
Results and Discussion
Recently, we developed a short and convenient
method for the stereoselective synthesis of terpene-
derived atropisomeric bipyridine N,N’-dioxides 7,
where substituents in the pyridine ring can be varied
through the choice of the starting ketone 8 (Scheme
2).[15] Where the desired substituent cannot be
introduced through the Kroenke annulation (9  11),
chemical modification of the available groups in
pyridine 11 may come to the rescue (e.g. 2-furyl
derivative 11i was transformed into nitrile 11c, see SI
for details). Notably, compound 7e exhibited
excellent enantiocontrol in the crotylation of
aldehydes;[16] therefore, it was reasonable to
investigate N,N’-dioxides 7 as catalysts in the
asymmetric propargylation. While 7 is different from
the original structures explored computationally (6),
they offer the practical advantage of being
9
10
11
7j, 2-Thienyl
a) The reactions were carried out on a 0.5 mmol scale in
CH2Cl2 at –60 ℃ under argon with 10 mol % of catalyst 7
for 18 hours. b) Conversion was calculated from GC data.
c)Determined by GC on a chiral column. Alcohol 3a was
d)
(S)-configured.
Catalyst (Sa)-7a, with phenyl substituents,
furnished alcohol 3a in 96% ee, providing a good
2
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10.1002/adsc.202000936
Advanced Synthesis & Catalysis
match with the theoretically predicted 88% ee for 6a
(entry 1).[14b] Its atropisomer (Ra)-7a, behaved in the
same way furnishing alcohol 3a of the opposite
enantiomeric series (entry 2). Analogues of other
catalysts that were predicted to show high levels of
dichloromethane in terms of both reactivity and
enantioselectivity (entries 7-11).
In the initial experiments, catalyst loading was kept at
10 mol% and the reactions were run for 18 h. Next,
these parameters were subjected to optimization
enantioselectivity proved less successful. For instance, employing the best performing catalysts, 7e and 7f
7c, with CN substituents, exhibited low reactivity
giving 3a in poor conversion, though with reasonable
69% ee (entry 4), whereas 7b (R = CF3) proved
completely inactive (entry 3). Catalyst 7d, with bulky
tBu substituents, also reacted sluggishly and resulted
in modest 50% ee (entry 5). The success of 7a
prompted us to investigate other aromatic substituents
(7e-7j). All the N,N’-dioxides containing aryl groups
in the -position to the N-oxide proved to be active
catalysts with high enantioselectivities (entries 6-9),
except for the heteroaromatic substituents where
enantiomeric excess dropped somewhat (entries 10,
11).
In the related allylation, solvent was shown to
exert an essential influence on the enantioselectivity
of the reaction by altering the operative reaction
mechanism.[17] Therefore, in the next stage, the effect
of solvent on propargylations was investigated.
Representative examples are collected in Table 2 (for
the full set of tests, see Tables S1-S3 in Supporting
Information).
(Table 3).
Table 3. Optimization of catalysts loading and the reaction
time.a
ee
entry catalyst 7, R
cat.
reaction conve
loading time (h) rsion (%)c
(mol.%)
(%)b
1
2
3
4
5
6
7
8
9
7e, 3,5-(CF3)2C6H3 10
0.25
0.25
0.5
1
2
3
3.5
0.5
0.5
1
3
8
99c
99c
98
91
96
7e, 3,5-(CF3)2C6H3
7e, 3,5-(CF3)2C6H3
7e, 3,5-(CF3)2C6H3
7e, 3,5-(CF3)2C6H3
7e, 3,5-(CF3)2C6H3
7e, 3,5-(CF3)2C6H3
7f, 4-ClC6H4
5
2
2
1
1
1
10
5
5
2
2
1
1
99c
66
97
93
99c
99c
90
98
98
7f, 4-ClC6H4
10 7f, 4-ClC6H4
11 7f, 4-ClC6H4
12 7f, 4-ClC6H4
13 7f, 4-ClC6H4
99c
69
98
97
94
99c
35
3
15
14 7f, 4-ClC6H4
58
a)
b)
The reactions were carried out at -60 ℃ under argon.
Table 2. Effect of solvent in addition of
trichloroallenylsilane 2 to benzaldehyde 1a.a
Conversion was calculated from GC data. c) Determined by
GC on a chiral column.
entry catalyst 7, R
solvent
convers ee,
ion, %b (%)
c
For catalyst 7e, with a loading of 10 or 5 mol%,
the reaction was complete in under 15 min (entries 1,
2). With 2 mol%, it took 30 min to reach nearly full
conversion, with the starting materials completely
disappearing after 1 h (entries 3, 4). Even with 1
mol%, the reaction finished in under 4 h (entries 5-7).
It is important to note that enantioselectivity
remained high at low catalyst loadings (entries 4, 7).
Bipyridine N,N’-dioxide 7f exhibited slightly reduced
reactivity compared to 7e. While with 10 and 5 mol%
it took under 1 h to achieve the complete conversion
(entries 8-10), going down to 2 mol% required 8 h,
whereas with 1 mol% the full conversion was not
reached even after 15 h (entries 11-14). However,
enantioselectivity stayed high irrespective of the
catalysts loading (entries 8, 10, 12, 14).
The optimization studies identified 7e as the
catalyst of choice, outperforming other N,N’-dioxides
in terms of the reactivity at low catalyst loadings and
excellent enantiocontrol. Therefore, it was taken
further for investigating the reaction scope. The
results are presented in Table 4.
With benzaldehyde 1a, the reaction worked well
both on a small (0.5 mmol) and a larger (9.4 mmol)
scale. For electron deficient aldehydes bearing nitro
or trifluoromethyl groups (1b, 1c and 1d)
enantioselectivity slightly dropped. Intriguingly, with
o-nitrobenzaldehyde the product with the opposite
absolute configuration was formed. In contrast, for
aldehydes with donor groups (1e-1h,) the selectivity
1
7a, Ph
7a, Ph
DCM
EtCN
99
≤5
99
14
70
99
85
≤5
43
7
96
76
93
93
93
72
37
80
74
40
40
2
3
7e, 3,5-(CF3)2C6H3 DCM
7e, 3,5-(CF3)2C6H3 EtCN
4
5
7g, 4-MeOC6H4
7g, 4-MeOC6H4
7g, 4-MeOC6H4
7g, 4-MeOC6H4
7g, 4-MeOC6H4
7g, 4-MeOC6H4
7g, 4-MeOC6H4
DCM
EtCN
THF
6
7
8
CHCl3
EtOAc
Ether
9
10
11
Toluene
9
a) The reactions were carried out on a 0.5 mmol scale at –
60 ℃under argon with 10 mol % of catalyst 7 for 18 hours.
b) Conversion was calculated from GC data. Determined
c)
by GC on a chiral column.
Dichloromethane appears to be the optimal
solvent, at least for the addition to benzaldehyde
(entries 1, 3, 5). In propionitrile (entries 2, 4, 6),
which served well in the related crotylation,[16a] the
results did not show any defined trend; however,
enantioselectivity was generally lower than in
dichloromethane. A number of other solvents were
tested with catalyst 7g and were clearly inferior to
3
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10.1002/adsc.202000936
Advanced Synthesis & Catalysis
remained excellent. Halide substituents, irrespective
of their nature or position around the ring (1i-1o), had
no effect on the enantioselectivity which stayed high.
reaction site. 2-Naphthaldehyde 1s mirrored the
reactivity of benzaldehyde 1a.
The set of electron-rich heteroaromatic aldehydes
1u-1w generally exhibited high enantioselectivities,
except for furfural 1t, which gave alcohol 3t in only
80% ee. Cinnamaldehyde 1x and 1-cyclohexen-1-
carboxaldehyde 1z reacted uneventfully, whereas -
methylcinnamaldehyde 1y gave the product 3y in
high ee but with the opposite absolute configuration.
Aliphatic aldehydes in Lewis-base catalyzed
alkylations generally react slower with lower
selectivity. The propargylation studied here was no
exception: aldehydes 1aa and 1ab showed selectivity
around 57% ee (cf. the respective -unsaturated
analogues 3x and 3z). Notably, 3-phenylpropanal 1aa
with catalyst 7e in CH2Cl2 gave only 38% ee in 32%
yield; the best result here was obtained with catalyst
7g in EtCN.
Table 4. Scope of asymmetric propargylation.a
a) The reactions were carried out on a 0.5 mmol scale under
argon at –60 ℃ for 8 h with 1 mol % of catalyst 7e, unless
stated otherwise. The absolute configuration of products 3
was R as assigned on the basis of literature data, unless
stated otherwise. The yield is shown for isolated yield.
Figure 1. a) Stereochemical model; b) Five possible
configurations of the hexacoordinate silicon intermediate
preceding the stereocontrolling TS; c) Lowest-lying TS
structures for the propargylation of benzaldehyde (1a)
catalyzed by 6a and 7a, along with relative energies in kcal
mol-1. Structures for 6a taken from Ref [14b]
.
Enantiopurity (shown in parenthesis) was determined by
b)
chiral GC or chiral HPLC, see SI for details.
The
reaction was performed on a 1.0 g (9.4 mmol) scale. c) The
reaction was carried out with catalyst 7g (10 mol%) in
EtCN at –60 ℃for 18 h.
We next turned to computations to compare the
key TS structures for selected examples of catalyst 7
with the previously studied catalysts 6. Wheeler et al.
previously showed[13] that the stereocontrolling C-C
bond forming step in these reactions can proceed via
five distinct configurations around the silicon (BP1-5,
For tolualdehydes 1p-1r, the position of the
substituent mattered, with the o-substituent affecting
the enantiocontrol the most. This is possibly due to
increased steric hindrance in the proximity of the
4
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10.1002/adsc.202000936
Advanced Synthesis & Catalysis
Figure 2. a) Lowest-lying TS structures for the propargylation of aldehydes 1a, 1b, and 1c catalyzed by 7e, along with
relative energies in kcal mol-1.
see Figure 1a), with the selectivity primarily
determined by the relative energy of the lowest-lying
TS structures leading to the two possible
stereoisomers. Studies of a model catalyst (2,2′-
bipyridine-N,N′-dioxide) revealed that configuration
BP2, with the chlorines in a cis arrangement and the
nucleophile trans to one of the N-oxides, is
energetically favoured by more than 1.5 kcal mol-1
over the configuration with a trans-Cl arrangement
(BP1).[14b] Consequently, for typical bipyridine-N,N′-
dioxide derived catalysts the favourable TS structures
exhibit configuration BP2.[14a] In these cases, the
selectivity stems from the presence of favourable
electrostatic interactions between the formyl CH and
the nearby Cl in the TS structure leading to the (R)-
alcohol (see Figure 1b). For catalysts bearing Ph
substituents at the 3,3′-positions, however, Doney et
al.[14b] showed that stacking and CH/π interactions
preferentially stabilize the TS structure derived from
configuration BP1 leading to the (S)-product,
resulting in different configurations around the Si for
the most favourable TS structures leading to each
stereoisomer. The selectivity then hinges on both the
inherent stability of BP2, relative to BP1, combined
with the net effect of non-covalent interactions in the
corresponding TS structures.
stability of BP2 over BP1, combined with the
balancing of stacking and CH/π interactions in both
low-lying TS structures (see Figure 1b).
We used the latest version of AARON[18] to
automatically compute all low-lying TS structures for
the propargylation of benzaldehyde (1a) catalyzed by
7a, 7e, and 7f at the PCM-B97-D/def2TZVP level of
theory (See SI for more details). In all three cases, the
lowest-lying TS structures are nearly identical to
those previously computed for 6a. For example, the
stereocontrolling TS structures for 7a are shown in
Figure 1c. Furthermore, the energy difference
between the stereocontrolling TS structures for 7a, 7e,
and 7f are similar to that computed for 6a (1.1 to 1.3
kcal mol-1, corresponding to 86-91% ee). While this
is not in exact quantitative agreement with the
experimental data, it is consistent with the observed
selectivities. Thus, while catalyst 7a, for example, is
not identical to the original catalyst design from
Ref.[14b] (i.e. 6a), it behaves very similarly and
achieves selectivity through the same mode identified
previously (See Figure 1b).[14b] Thus, the
experimental data presented for 7a provides at least
indirect verification of the previous computational
predictions for 6a.[14b]
We also considered the propargylations of
aldehydes 1b and 1c catalyzed by 7e (i.e. entries 3
and 4 from Table 4) to understand the impact of nitro
substituents on the selectivity of this reaction. The
key TS structures for aldehydes 1a, 1b, and 1c are
shown in Figure 2. First, the lowest-lying (R) and
(S)-TS structures for 1a and 1c are nearly identical to
those pictured in Figure 1c for 7a. For benzaldehyde
(1a), the energy difference between the key
stereocontrolling TS structures, TS-7e-R(1a) and TS-
The primary stereocontrolling TS structures from
Ref.[14b] for 6a are depicted in Figure 1c, with TS(R)
lying 1.1 kcal mol-1 lower in energy than TS(S). As
with other catalysts bearing Ph substituents at the
3,3′-positions, the lowest-lying TS structure leading
to the (R)-alcohol (TS-6a-R) exhibits configuration
BP2 while the most favourable TS leading to the (S)-
product (TS-6a-S) follows BP5. The selectivity can
then be attributed to the combination of the inherent
5
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10.1002/adsc.202000936
Advanced Synthesis & Catalysis
7e-S(1a), is 1.2 kcal mol-1. For p-nitrobenzaldehyde
(1c), this energy difference is reduced to 0.7 kcal mol-
1, consistent with the experimental observation of
reduced selectivity (i.e. entry 3 vs entry 1 in Table 4).
Examining the structures in Figure 2, the reduced
selectivity in the latter case can be explained by the
modulation of the π-stacking interaction between the
aromatic aldehyde and one of the bis-CF3-phenyl
groups of the catalyst in the (S)-TS structure. For
aldehyde 1c, the presence of a p-nitro group enhances
the stacking interaction in the (S)-TS structure, due to
the well-established substituent effects in π-stacking
interactions,[19] leading to stabilization of the
disfavored TS and reduced selectivity.
In the case of o-nitrobenzaldehyde (1b), while
computations indicate a further lowering of the
energy of the (S)-TS compared to that for (R), these
data are not consistent with the experimental
observation of reversed stereoselectivity. However,
the results do show a qualitative change in the
structure of the lowest-lying TS leading to the (R)-
alcohol along with major changes in the energetic
ordering of the possible TS structures for this reaction.
More precisely, while the lowest-lying (S)-TS
structure, TS-7e-S(1b), is similar to that found for 1a
and 1c, the most favorable TS structure leading to the
(R)-alcohol, TS-7e-R(1b), instead exhibits the same
trans-chlorine configuration as TS-7e-S(1b). The
structures for 1c analogous to those from 1a and 1c
(not shown) is 0.6 kcal mol-1 higher in energy than
TS-7e-R(1b). Overall, these results suggest that the
stereoreversal in the case of aldehyde 1b can be
attributed to the elimination of the favoured cis-
chlorine pathway leading to the (R)-alcohol that is
accessible for the other aldehydes.
Experimental Section
General procedure for asymmetric propargylation
The solution of allenyltrichlorosilane (0.71 mmol, 1.5
equiv) in 0.5 mL DCM was added to a solution of catalyst
(0.0047 mmol, 1 mol%), diisopropylethylamine (0.71
mmol, 1.5 equiv) and aldehyde (0.47 mmol) in DCM (1.5
mL) under argon at -60 °C. The mixture was stirred at the
same temperature for 8 hours and then quenched with
saturated NH4Cl solution (2mL). The aqueous layer was
extracted with Et2O (3 x 20 mL) and the combined organic
extracts were washed with brine and dried over Na2SO4.
The solvent was removed in vacuo and the residue was
purified by flash chromatography on silica gel with a
petroleum ether–ethyl acetate mixture 9:1. The
enantiopurity of the resulting alcohols was determined by
GC or HPLC with a chiral sorbents. The absolute
configurations were assigned by comparing optical rotation
values to the literature.
Acknowledgements
This work was supported by Russian Science Foundation Grant
18-73-10156 (Chemical part) and National Science Foundation
Grant CHE-1665407 (Computational part). YF thanks the
Japanese Government and the Loughborough University for a
studentship. Portions of this work were conducted using high
performance computing resources provided by the Georgia
Advanced Computing Resource Center (http://gacrc.uga.edu).
Molecular structure figures were generated using the SEQCROW
plugin[20] for ChimeraX.[21]
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Conclusion
Guided by previously reported computational
predictions,[14b] a set of atropisomeric bipyridine
N,N’-dioxides 7a-7j were synthesized and tested as
Lewis base catalysts for the asymmetric
propargylation
of
aldehydes
with
trichloroallenylsilane. The catalysts are easy to
prepare in four simple steps starting from methyl
ketones readily available from commercial sources.
Aryl-substituted derivatives proved to be highly
active and showed high level of enantiocontrol;
catalyst 7e was identified as the most efficient,
retaining high reactivity even at 1 mol% loading.
Computations confirm that the key stereodetermining
TS structures for this and other highly active and
selective catalysts are nearly identical in most cases
to those previously reported for catalyst 6a.[14b] The
reaction scope includes a wide range of aromatic,
heteroaromatic and unsaturated aldehydes, whereas
aliphatic aldehydes proved to be challenging
substrates.
[3] T. Thaima, F. Zamani, C. J. T. Hyland, S. G. Pyne,
Synthesis 2017, 49, 1461-1480.
[4] a) M. Z. Wang, S. Khan, E. Miliordos, M. Chen, Org.
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FULL PAPER
Optimization of Catalyst Structure for Asymmetric
Propargylation of Aldehydes with
Allenyltrichlorosilane
Adv. Synth. Catal. Year, Volume, Page – Page
Vladimir Yu. Vaganov, Yasuaki Fukazawa,
Nikolay S. Kondratyev, Sergei A. Shipilovskikh,
Steven E. Wheeler, Aleksandr E. Rubtsov,* and
Andrei V. Malkov*
8
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