Gold-Catalyzed Rearrangement of (Silylcyclopropenyl)methyl Ethers into (Silylmethylene)cyclopropanes

Article abstract of DOI:10.1055/s-0035-1561486

Methoxymethyl ethers derived from 2-(dimethylphenylsilyl)cycloprop-1-enyl carbinols undergo gold-catalyzed rearrangement leading to [(Z)-(dimethylphenylsilyl)methylene]cyclopropanes in moderate to high yields with methyl formate as a byproduct. This transformation proceeds by initial regioselective ring opening of the three-membered ring leading to an α-silyl vinyl gold carbenoid. This latter organogold species evolves by 1,5-hydride transfer, which triggers subsequent rearrangement involving loss of methyl formate, 2π-electrocyclization of the resulting allylic cation, and elimination of the metal to regenerate the catalyst.

Full text of DOI:10.1055/s-0035-1561486

SYNTHESIS
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© Georg Thieme Verlag Stuttgart · New York
2016, 48, 3165–3174
paper
3165
F. Hiault et al.
Paper
Synthesis
Gold-Catalyzed Rearrangement of (Silylcyclopropenyl)methyl
Ethers into (Silylmethylene)cyclopropanes
Florence Hiault
Alexis Archambeau
Frédéric Miege
Regioselective
ring-opening
Rearrangement
triggered by
1,5-hydride
transfer
Me
Me
Me
Me
Me
Me
R
R
[Au]
R
AuCl (5 mol%)
PhMe2Si
PhMe2Si
H
Christophe Meyer*
Janine Cossy*
H
CH2Cl2
r.t., 8–16 h
O
PhMe2Si
H
O
H
O
H
H
(36–95%)
OMe
OMe
(CH2)2
10 examples
OMe
Laboratory of Organic Chemistry, Institute of Chemistry,
Biology and Innovation (CBI) ESPCI Paris, CNRS
(UMR8231), PSL Research University, 10 rue Vauquelin,
75231 Paris Cedex 05, France
R = CH OBn, (CH ) OTBS, (CH ) Ph, (CH ) CH=CH ,
TMS
, Ph, 2-FC6H4, i-Pr, CH(Me)Ph
2
2 3
2 2
2 3
2
christophe.meyer@espci.fr
janine.cossy@espci.fr
Dedicated to the memory of Professor Jean-François Normant, a remarkable mentor and scientific personality.
Received: 13.05.2016
Accepted after revision: 08.06.2016
Published online: 27.07.2016
afard, et al. reported the gold-catalyzed isomerization of
cyclopropenylmethyl acetates A into 2-acetoxy-1,3-dienes
that proceeds by regioselective ring opening to generate the
gold carbenoid B at C1 followed by 1,2-acetoxy shift and
elimination of the metal.5c Our group has shown that allyl
ethers D derived from 3,3-dimethylcyclopropenyl carbinols
underwent regioselective ring opening to generate gold
carbenoids E at C2, which effected the highly diastereose-
lective intramolecular cyclopropanation of the remote ole-
fin to afford 3-oxabicyclo[4.1.0]heptanes F.6c,d The substitu-
ents of the cyclopropene double bond in cyclopropenyl car-
DOI: 10.1055/s-0035-1561486; Art ID: ss-2016-c0350-op
Abstract Methoxymethyl ethers derived from 2-(dimethylphenylsi-
lyl)cycloprop-1-enyl carbinols undergo gold-catalyzed rearrangement
leading to [(Z)-(dimethylphenylsilyl)methylene]cyclopropanes in mod-
erate to high yields with methyl formate as a byproduct. This transfor-
mation proceeds by initial regioselective ring opening of the three-
membered ring leading to an α-silyl vinyl gold carbenoid. This latter or-
ganogold species evolves by 1,5-hydride transfer, which triggers subse-
quent rearrangement involving loss of methyl formate, 2π-electrocy-
clization of the resulting allylic cation, and elimination of the metal to
regenerate the catalyst.
binol derivatives
A and D were crucial to achieve
regioselective ring opening. DFT calculations by Hyland,
Ariafard, et al. indicated that the regioselectivity of the ring
opening of a cyclopropene in the presence of a gold(I) com-
plex is governed by the relative π-donating abilities of sub-
stituents at C1 and C2.8,9 This study accounts well for the
observed regioselectivities of the ring opening of cyclopro-
penes A and D because the π-donating abilities of the sub-
stituents vary in the following order Me > CH(OR) > H.8
Herein, we report a new gold-catalyzed rearrangement
of ethers derived from silylcyclopropenyl carbinols G,
which leads to (silylmethylene)cyclopropanes I and pro-
ceeds by rearrangement of α-silyl vinyl gold carbenoids H
triggered by a 1,5-hydride transfer (Scheme 1).
With the goal of extending the scope of the gold-cata-
lyzed cycloisomerization of 1,6-cyclopropene-enes D, the
reactivity of related substrates possessing a substituent at
C2 was investigated. However, π-donating groups able to
stabilize an adjacent positive charge would alter the regio-
selectivity of the ring opening and favor the formation of a
regioisomeric gold carbenoid at C1.6c We reasoned that a si-
lyl group should not alter the regioselectivity of the ring
opening because of the β effect of silicon,10 although DFT
calculations indicated that the ring opening of (trimethylsi-
Key words cyclopropenes, gold catalysis, strained cycles, rearrange-
ment, hydride transfer
Transition-metal-catalyzed reactions of cyclopropenes
have attracted considerable mechanistic and synthetic in-
terest.1,2 Indeed, transition metals are able to catalyze the
addition of several reagents across the carbon–carbon dou-
ble bond of cyclopropenes but also a variety of transforma-
tions accompanied by ring cleavage.1,2 It is well known that
many electrophilic metal complexes can trigger the ring
opening of cyclopropenes to generate vinyl metal carben-
oids that can undergo nucleophilic additions or rearrange-
ments or be involved in cyclopropanation or C–H insertion
reactions.1,2 In 2008, the groups of Shi3 and Lee4 disclosed
the first examples of gold(I)-catalyzed reactions of cyclo-
propenes. Their pioneering work and subsequent contribu-
tions demonstrated that the gold carbenoids resulting from
the ring opening of cyclopropenes can participate in the in-
ter- or intramolecular addition of nucleophiles3–6 and in
olefin cyclopropanation.6 Cyclopropenyl carbinol deriva-
tives, readily available by addition of cyclopropenyl organo-
lithium reagents to aldehydes,7 have been successfully in-
volved in gold-catalyzed reactions. To date, Hyland, Ari-
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, 3165–3174

3166
F. Hiault et al.
Paper
Synthesis
group altered the reactivity and suppressed the intramolec-
ular olefin cyclopropanation process. At this stage, the fate
of the allyloxy group of 1a, which is not present in the rear-
ranged product 2, remained uncertain. This issue was
solved by examination of the reactivity of the structurally
related (trimethylsilyl)cyclopropene 1b possessing a benzyl
ether. The gold-catalyzed rearrangement of 1b proceeded
under equally mild conditions and also produced (silyl-
methylene)cyclopropane 2 (87%), but in this case benzalde-
hyde (3b) was identified as the byproduct. This finding sug-
gested that acrolein 3a had presumably been generated as a
volatile byproduct during the gold-catalyzed rearrange-
ment of 1a but was lost during workup (Scheme 2).
Previous gold-catalyzed reactions of cyclopropenyl carbinol
derivatives:5c,6c,d
–
Me
3
Me
Me
Me
Me
Me
Me
3
2
3
NTf2
R
4
(Ph3P)AuNTf2
(5 mol%)
4
1
+
4
R
1
1
2
2
Me
O
Me
R
CH2Cl2
–40 °C
(Ph3P)Au
OAc
OAc
C (80–89%)
O
A
B
Me
3
1
Me
3
Me
Me
Me
Me
3
1
2
1
4
[Au]
R3
2
4
R
R
H
AuCl
R1
R
4
R2
R3
R1
(5 mol%)
2
R3
O
O
CH2Cl2
0 °C
O
R1
R2
R2
D
E
F (84–99%)
To explain the formation of alkylidenecyclopropane 2
from [(trimethylsilyl)cyclopropenyl]methyl ethers 1a and
1b, a plausible mechanism would involve initial regioselec-
tive ring opening of the three-membered ring to generate
the corresponding α-trimethylsilyl vinyl gold carbenoids 4a
and 4b at C2. Coordination of the gold moiety to the C1–C2
double bond with unsymmetrical binding through C2
would induce a partial charge depletion at C1,9 stabilized by
the silicon β effect.10 The electrophilic organogold carben-
oids 4a and 4b would then undergo 1,5-hydride transfer,
assisted by the oxygen atom,13 producing the corresponding
α-silyl allyl gold complexes 5a and 5b with an oxonium ion
leaving group at C4. The rearrangement of these latter spe-
cies into (silylmethylene)cyclopropane 2 would then in-
volve three elementary key steps: (i) ionization of the C4–O
bond with elimination of acrolein or benzaldehyde,14 (ii) a
2π-electrocyclization leading to the formation of the C3–C4
bond and hence constructing a three-membered ring, and
(iii) the elimination of the gold moiety resulting in the for-
mation of the C2=C1 alkenylsilane moiety in compound 2
(Scheme 3).
This work :
Me
3
1
Me
3
Me
Me
3
Me
Me
2
1
4
2
[Au]
4
R
R
AuCl
1
2
4
R'3Si
R'3Si
O
(5 mol%)
O
CH2Cl2
R
R'3Si
H
O
H
H
H
R''
G
R''
H
R''
I
Scheme 1 Gold-catalyzed reactions of cyclopropenyl carbinol deriva-
tives
lyl)cyclopropene would produce an α-silyl vinyl gold car-
benoid with a very modest preference.8 1,2-Silyl migration
could also occur, as observed in the platinum-catalyzed
isomerization of silylcyclopropenes into silylallenes.11
(Trimethylsilyl)cyclopropene 1a was prepared and
treated with a catalytic amount of AuCl (5 mol%) in CH2Cl2
(r.t., 2 h). A clean reaction occurred and analysis of the
1
crude material by H NMR spectroscopy indicated the for-
mation of a new compound which was identified as [(Z)-
(trimethylsilyl)methylene]cyclopropane 2. This compound
was formed with high stereoselectivity (Z/E ≥ 95:5)12 and
isolated in 85% yield. Interestingly, the presence of the silyl
3
Me
Me
3
Me
Me
AuCl
1
4
4
(5 mol%)
R
OBn
O
Me3Si
2
1
Me3Si
OBn
+
2
CH2Cl2, r.t.
R
O
H
H
3
1a, R = CH=CH2
1b, R = Ph
3a, R = CH=CH2
3b, R = Ph
Me
Me
2
Me
3
Me
AuCl
(5 mol%)
CHO
4
2
1
Me3Si
OBn
OBn
Me3Si
OBn
+
[Au]
– [Au]
1
4
CH2Cl2
r.t., 5 h
2
O
3
1
3
Me
Me
4
Me
Me
1a
2 (85%)
(E/Z ≥ 95:5)
3a
iii
ii
1,5-hydride
transfer
[Au]
– [Au]
Me3Si
Me
Me
4
1
3
OBn
OBn
4
2
2
3
Me
Me
i
AuCl
(5 mol%)
H
Me3Si
O
H
O
+
2
1
Me3Si
Me3Si
OBn +
PhCHO
1
4
CH2Cl2
r.t., 3 h
R
2
R
Ph
O
4a, R = CH=CH2
4b, R = Ph
5a, R = CH=CH2
3b
1b
2 (87%)
(E/Z ≥ 95:5)
5b, R = Ph
Scheme 3 Plausible mechanism accounting for the formation of (silyl-
methylene)cyclopropane 2 from 1a and 1b
Scheme 2 Gold-catalyzed rearrangement of allyl and benzyl silylcyclo-
propenylmethyl ethers 1a and 1b
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, 3165–3174

3167
F. Hiault et al.
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Synthesis
The occurrence of a 1,5-hydride transfer was confirmed
by the rearrangement of the gem-deuterated benzyl ether
1b′ which selectively produced (silyldeuteromethylene)cy-
clopropane 2′ (89%) and deuterated benzaldehyde 3b′
(Scheme 4).
chromatography from the rearranged products. For these
reasons, [(dimethylphenylsilyl)cyclopropenyl]methyl meth-
oxymethyl (MOM) ethers K were eventually selected as
substrates. Indeed, their synthesis from cyclopropenyl car-
binols J would not require strongly basic conditions and
their gold-catalyzed rearrangement into (silylmethy-
lene)cyclopropanes L would produce methyl formate as a
volatile byproduct (Scheme 5).
Me
Me
3
Me
Me
3
AuCl
Ph
+
O
(5 mol%)
4
1
4
2
1
Me3Si
OBn
Me3Si
OBn
Several
[(dimethylphenylsilyl)cyclopropenyl]methyl
CH2Cl2
r.t., 3 h
2
D
Ph
O
ethers were prepared by addition of the organolithium
reagent 7, generated from silylcyclopropene 6 (n-BuLi, THF,
–78 °C to –10 °C), to various aldehydes (–50 °C to –10 °C)
followed by conversion of the resulting secondary alcohols
8a–j/8j′ into the corresponding MOM ethers under stan-
dard conditions (MOMCl, i-Pr2NEt, CH2Cl2, 0 °C to r.t.). The
resulting ethers 9a–j/9j′ were isolated in 15% to 90% overall
yields (two steps from the corresponding aldehydes) with-
out any optimization. When 2-phenylpropionaldehyde was
used as the substrate, an inseparable 90:10 mixture of
syn/anti diastereomers 9j/9j′ was obtained (75% overall
yield), as a result of a Felkin–Anh addition mode of the cy-
clopropenyl organolithium reagent 7 (Scheme 6).17,18
D
3b'
(>96% D)
2' (89%)
D
D
(>96% D)
1b'
Scheme 4 Gold-catalyzed rearrangement of gem-dideuterated benzyl
ether 1b′
It is worth pointing out that the rearrangement of the
cyclopropenylmethyl ether 1b into (silylmethylene)cyclo-
propane 2 shares some similarities with the gold-catalyzed
rearrangement of benzyl propargyl ethers into allenes,
which proceeds by 1,5-hydride shift onto alkynes activated
by the gold(I) complex and subsequent fragmentation with
loss of benzaldehyde.15
Before studying the scope of this new gold-catalyzed re-
arrangement, our attention was drawn to the search for al-
ternative (silylcyclopropenyl)methyl ether substrates. In-
deed, a dimethylphenylsilyl substituent rather than a
trimethylsilyl group would potentially offer more opportu-
nities for further functionalization of the carbon–silicon
bond.16 Additionally, the corresponding silylated cyclopro-
penyl carbinol precursors J would be easily obtained by ad-
dition of the organolithium generated from the non-volatile
and readily available 3,3-dimethyl-1-(dimethylphenylsi-
lyl)cyclopropene (6)17 to various aldehydes. However, al-
lylation or benzylation of silylcyclopropenyl carbinols J can-
not be conveniently achieved under the usual basic condi-
tions (NaH or t-BuOK, Allyl-Br or BnBr, THF) because
competitive cleavage of the C–Si bond occurred. Benzyl
ethers were also not appealing substrates because the non-
volatile byproduct benzaldehyde has to be separated by
The initial screening of the reaction conditions was car-
ried out with substrate 9a. As observed previously with the
allyl and benzyl ethers 1a and 1b (Scheme 2), the rear-
rangement of MOM ether 9a was efficiently catalyzed by
AuCl (5 mol%) (CH2Cl2, r.t., 8 h), albeit a slightly longer reac-
tion time was required. The [(Z)-(dimethylphenylsi-
lyl)methylene]cyclopropane 10a was formed as a single
geometric isomer and was isolated in 86% yield.12 Because
AuCl does not lead to a well-defined catalyst in CH2Cl2,19 the
20
use of the gold(I) complexes (Ph3P)AuNTf2 and [Au]-I21
was also attempted. Although substrate 9a was rapidly con-
sumed with these catalysts, the formation of 10a was im-
mediately accompanied by numerous side products that
could not be readily separated or identified.22 By contrast,
the rearrangement of 9a catalyzed by the gold(III) complex
[Au]-II23 provided 10a in good yield (74%) (Scheme 7).
The best result was obtained with AuCl which was
hence used as a catalyst for the investigation of the rear-
rangement of the other substrates 9b–j/9j′ (Table 1).
The gold-catalyzed rearrangement of ether 9b possess-
ing a (3-silyloxypropyl) substituent proceeded well and
provided compound 10b in 74% yield (Table 1, entry 1). The
reaction is compatible with a phenyl group or a terminal
alkene on the chain as shown with compounds 9c and 9d,
respectively, which afforded the corresponding al-
kylidenecyclopropanes 10c (78%) and 10d (74%) (Table 1,
entries 2 and 3). Interestingly, a (trimethylsilyl)alkyne did
not interfere, as illustrated in the case of substrate 9e which
underwent an efficient chemoselective rearrangement
leading to methylenecyclopropane 10e in 86% yield (Table
1, entry 4).24 The reactivity of arylmethyl ethers 9f–h was
next examined. The rearrangement of the phenyl-substitut-
Me
Me
3
Me
Me
3
gold
catalyst
R
4
H
O
2
1
1
2
4
PhMe2Si
PhMe2Si
+
R
H
O
OMe
H
L
6
OMe
K
MOMCl, i-Pr2NEt
Me
Me
Me
Me
H
R
O
R
+
PhMe2Si
PhMe2Si
H
J
OH
Scheme 5 Selection of [(dimethylphenylsilyl)cyclopropenyl]methyl
MOM ethers K as substrates for gold-catalyzed rearrangement
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, 3165–3174

3168
F. Hiault et al.
Paper
Synthesis
conditions (Table 1, entry 6). The rearrangement of 9h pos-
sessing a 2-fluorophenyl group produced alkylidenecyclo-
propane 10h in low yield (36%) (Table 1, entry 7). Thus,
ethers derived from aryl cyclopropenyl carbinols were not
viable substrates in this gold-catalyzed rearrangement.
Branched alkyl groups were tolerated as illustrated by the
gold-catalyzed rearrangement of cyclopropenylsilane 9i
substituted by an isopropyl group which produced al-
kylidenecyclopropane 10i (90%) (Table 1, entry 8). The rear-
rangement of the diastereomeric mixture of 9j/9j′ (syn/anti
90:10) also proceeded efficiently, but provided a mixture of
the corresponding alkylidenecyclopropane diastereomers
10j and 10j′ in 65:35 ratio (81%) (Table 1, entry 9). A mix-
ture of 9j/9j′ with inverted diastereomeric ratio (9j/9j′
23:77) was also prepared (by oxidation of the mixture of
9j/9j′ and reduction of the resulting ketone with DIBAL-H)
and involved in the gold-catalyzed rearrangement. The dia-
stereomeric alkylidenecyclopropanes 10j/10j′ were then
formed in a 43:57 ratio (77%) (Table 1, entry 10).
Me
Me
Me
Me
n-BuLi
PhMe2Si
H
PhMe2Si
RCHO
Li
6
THF, –78 °C to –10 °C
7
−50 °C to −10° C
Me
Me
Me
Me
MOMCl, i-Pr2NEt
R
R
CH2Cl2, 0 °C to r.t.
PhMe2Si
PhMe2Si
Me
OMOM
Me
OH
9a–j
Me
8a–j
Me
PhMe2Si
OBn
OMOM
9a (62%)a
Me
PhMe2Si
OTBS
OMOM
9b (50%)a
Me
Me
Me
Ph
PhMe2Si
PhMe2Si
OMOM
(75%)a
OMOM
(76%)a
9d
The erosion of the diastereomeric ratio in the gold-cata-
lyzed rearrangement of epimeric substrates 9j/9j′ seems to
point toward a non-stereospecific rearrangement process.
Therefore, the behavior of the enantioenriched substrate 9a
was investigated to gain further insight into the mecha-
nism.
9c
R
R'
Me
Me
Me
Me
TMS
PhMe2Si
PhMe2Si
OMOM
9e (87%)a
OMOM
9f, R = R' = H
9g, R = H, R' = OMe (29%)a
9h, R = F, R' = H
Me Me
(90%)a
(74%)a
Considering the similarities between cyclopropenes and
alkynes,25 we surmised that the ruthenium(II)-catalyzed
enantioselective hydrogenation transfer26 of silylcyclopro-
penyl ketones could provide access to optically enriched si-
lylcyclopropenyl carbinols. Effectively, cyclopropenyl ke-
tone 11, prepared by oxidation of the racemic alcohol (±)-8a
using Dess–Martin periodinane (DMP), successfully under-
went chemoselective hydrogenation transfer in isopropyl
alcohol in the presence of Noyori’s catalyst (R,R)-[Ru]-I26
(3 × 6 mol%) (r.t. to 40 °C). Although the conditions were
not optimized, the optically active silylcyclopropenyl carbi-
nol (R)-8a was obtained in good yield (74%) and with a de-
cent enantiomeric excess (75% ee). The absolute configura-
tion of this latter alcohol was not determined unambigu-
ously but assigned by analogy with the known face-
Me
Me
Me
Me
PhMe2Si
Ph
OMOM
PhMe2Si
Me
OMOM
9i (15%)a
a
(syn/anti = 90:10)
9j/9j'
(75%)
Scheme 6 Preparation of the [(dimethylphenylsilyl)cycloprope-
nyl]methyl MOM ether substrates 9a–9j/9j′. a Overall yield from the
corresponding aldehydes (two steps).
ed substrate 9f led to compound 10f albeit in moderate
yield (49%) (Table 1, entry 5), because of competitive forma-
tion of unidentified byproducts. Substrate 9g possessing an
electron-rich aromatic ring decomposed under the reaction
Me
Me
3
Me
Me
3
catalyst (5 mol%)
4
2
1
PhMe2Si
OBn
PhMe2Si
OBn
1
4
2
CH2Cl2, r.t.
OMOM
9a
10a
(− HCOOMe)
– SbF6
t-Bu
t-Bu
+
Catalyst
Reaction time
Yield
P
Au(NCMe)
O
N
AuCl
(Ph3P)AuNTf2
[Au]-I
8 h
2 h
2 h
86%
trace
trace
Cl Au
Cl
O
[Au]-II
8 h
74%
[Au]-I
Scheme 7 Gold-catalyzed rearrangement of MOM ether 9a
[Au]-II
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Synthesis
Table 1 Gold-Catalyzed Rearrangement of Substrates 9b–j/9j′
Me Me
selectivity of the hydrogenation transfer of acetylenic ke-
tones, considering the π-donating character of a cyclopro-
pene.27 The enantioenriched cyclopropenylmethyl ether
(R)-9a was then prepared from (R)-8a and involved in the
gold-catalyzed rearrangement. The formation of racemic
(silylmethylene)cyclopropane (±)-10a (95%) confirmed the
non-stereospecific character of the gold-catalyzed rear-
rangement (Scheme 8).
Me
Me
AuCl (5 mol%)
R
PhMe2Si
PhMe2Si
CH2Cl2, r.t., 8–16 h
R
OMOM
(Z/E > 96:4)
9b–j/9j'
Entry Substrate
10b–j/10j'
Product
Yielda (%)
Me
Me
Me
Me
Me
Me
Me
Me
1
2
9b
9c
74
78
DMP
PhMe2Si
OTBS
PhMe2Si
OBn
PhMe2Si
OBn
10b
CH2Cl2
OH
O
( )-8a
0 °C to r.t.
93%
11
Me
Me
PhMe2Si
Me
Ph
10c
(R,R)-[Ru]-I
(3 x 6 mol%)
i-PrOH, r.t. to 40 °C
Ru
74%
TsN
Ph
NH
Ph
Me
Me
Me
Me
3
4
9d
9e
74
86
PhMe2Si
(R,R)-[Ru]-I
10d
Me
Me
OR
Me
Me
AuCl
(5 mol%)
PhMe2Si
OBn
PhMe2Si
OBn
PhMe2Si
CH2Cl2, r.t.
95%
( )-10a
(ee = 0%)
TMS
(ee = 75%)
(R)-8a R = H
10e
MOMCl, i-Pr2NEt
CH2Cl2, 0 °C to r.t.
Me
Me
Me
Me
(R)-9a R = MOM
82%
PhMe2Si
Scheme 8 Preparation and gold-catalyzed rearrangement of optically
active MOM ether (R)-9a
5
6
9f
49
10f
After regioselective ring opening of cyclopropenes K
and 1,5-hydride transfer to the α-(dimethylphenylsilyl)
gold carbenoids M, the rearrangement of the resulting allyl-
ic organogold species N into (silylmethylene)cyclopropanes
L likely involves the dissociation of the C4–O bond with
elimination of methyl formate to a large extent, if not com-
pletely as in the case of substrate (R)-9a for which complete
racemization occurs. The C3–C4 bond would then be creat-
ed by 2π-electrocyclization of the allylic cation O followed
by formation of the C1–C2 double bond by elimination of
gold. The stereoselectivity of this latter step is difficult to
explain at this stage, but the isopropylidene substituent is
presumably acting as a key element for the control of the
conformation around the C1–C2 and C1–C4 in the cationic
intermediate O (Scheme 9).28
The reactivity of the (silylmethylene)cyclopropanes L
produced by the gold-catalyzed rearrangement of MOM
ethers K is still under investigation. We have shown so far
that the diastereoselective hydrogenation of the exocyclic
alkene could be achieved (H2, cat. Pd/C, EtOAc, r.t.) (on the
face opposite to the silyloxypropyl chain) to afford the cis-
disubstituted cyclopropane 12 (88%) (Scheme 10).
PhMe2Si
9g
9h
–
OMe
10g
Me
Me
PhMe2Si
7
8
36
90
F
10h
Me
Me
Me
PhMe2Si
Me
9i
Me
10i
Me
Me
9j/9j′
PhMe2Si
Ph
H
9j/9j′
(dr 90:10)
9
10j/10j′ 65:35
10j/10j′ 43:57
81
77
9j/9j′
(dr 23:77)
10
a Isolated yield of analytically pure material.
© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, 3165–3174

3170
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Synthesis
MHz referenced to the solvent signal (δ = 77.16 for CDCl3) and include
carbon environment (deduced from DEPT experiments). HRMS (ESI)
were obtained with an orbitrap mass analyzer. Enantiomeric purities
were determined by supercritical fluid chromatography (SFC) on a
Minigram Berger SFC-Mettler Toledo apparatus equipped with a chi-
ral stationary phase.
3
Me
Me
3
Me
Me
AuCl (5 mol%)
CH2Cl2, r.t.
4
R
1
2
1
PhMe2Si
PhMe2Si
4
R
H
O
2
K
L
OMe
[Au]
The preparation of silylcyclopropenes 1a, 1b, 1b′, 9b–j/9j′ is detailed
in the Supporting Information.
– [Au]
Me
"Si" = SiMe2Ph
3
Me
Me
Me
3
Me
3
1
Me
Gold-Catalyzed Rearrangement of Cyclopropenes 1a, 1b, and 1b′
1
[Au]
[Au]–
"Si"
4
[Au]
R
R
2
H
+
1
2
4
({(1Z)-3-[(Benzyloxy)methyl]-2,2-dimethylcyclopro-
pylidene}methyl)trimethylsilane (2)
4
H
"Si"
2
"Si"
O
O
+
H
H
R
H
O
To a solution of silylcyclopropene 1a (52 mg, 0.16 mmol) in CH2Cl2
(3 mL) at r.t., was added AuCl (1.8 mg, 0.0077 mmol, 5 mol%). The
mixture was stirred for 5 h and then it was filtered through Celite
(CH2Cl2). The filtrate was evaporated under reduced pressure and the
crude material was analyzed by 1H NMR spectroscopy, which indicat-
ed the formation of 2 with high stereoselectivity (Z/E >95:5). The
crude material was purified by flash column chromatography (petro-
leum ether/EtOAc, 98:2 to 96:4) to give 2 (37 mg, 85%) as a yellow oil.
Compound 2 (46 mg, 87%) was also obtained by the gold-catalyzed
rearrangement of silylcyclopropene 1b and in this case benzaldehyde
was detected by analysis of the crude material by 1H NMR spectrosco-
py.
MeO
OMe
N
OMe
M
O
Scheme 9 Plausible mechanism accounting for the formation of (silyl-
methylene)cyclopropane 2 from 1a and 1b
OTBS
Me
Me
H2
OTBS
Me
Me
H
H
Pd/C (5 mol%)
PhMe2Si
EtOAc, r.t.
SiMe2Ph
12 (dr > 95:5)
10a
Scheme 10 Diastereoselective hydrogenation of 10a
IR (neat): 1730, 1454, 1365, 1246, 1090, 1075, 862, 835, 734, 695 cm–1
.
1H NMR (400 MHz, C6D6): δ = 7.43 (br d, J = 7.4 Hz, 2 H), 7.31–7.27 (m,
2 H), 7.20 (m, 1 H), 6.10 (d, J = 1.8 Hz, 1 H), 4.50 (d, AB syst, J = 12.2 Hz,
1 H), 4.45 (d, AB syst, J = 12.2 Hz, 1 H), 3.70 (dd, J = 10.5, 5.7 Hz, 1 H),
3.42 (dd, J = 10.5, 9.1 Hz, 1 H), 1.66 (ddd, J = 9.1, 5.7, 1.8 Hz, 1 H), 1.29
(s, 6 H), 0.25 (s, 9 H).
In summary, we have disclosed a new transition-metal-
catalyzed process involving cyclopropenyl carbinol deriva-
tives that complements the transformations in which these
latter substrates have been involved so far. In the presence
of gold chloride, MOM ethers derived from (dimethylphe-
nylsilyl)cyclopropenyl carbinols undergo rearrangement to
[(dimethylphenylsilyl)methylene]cyclopropanes and meth-
yl formate. We have provided evidence that the key steps of
this rearrangement involve regioselective ring opening of
the cyclopropene ring leading to an α-silyl gold carbenoid
and 1,5-hydride transfer, which triggers subsequent elimi-
nation of methyl formate, 2π-electrocyclization of the re-
sulting allylic cation, and elimination of the metal. Further
investigation of the scope of this transformation as well as
on the reactivity of the corresponding (silylmethylene)cy-
clopropane products are underway.
Signals observed at 6.13 (d, J = 2.3 Hz, 1 H) and 3.85 (dd, J = 10.3, 5.3
Hz, 1 H), 1.78 (ddd, J = 9.7, 5.3, 2.3 Hz, 1 H) were tentatively assigned
to the E-geometric isomer (dr >95:5).
13C NMR (100 MHz, CDCl3): δ = 154.6 (C), 138.8 (C), 128.5 (2 CH),
127.8 (2 CH), 127.6 (CH), 116.9 (CH), 72.6 (CH2), 69.5 (CH2), 27.2
(CH3), 26.5 (CH), 20.9 (C), 19.5 (CH3), –0.5 (3 CH3).
HRMS (ESI): m/z [M + Na+] calcd for C17H26ONaSi: 297.16466; found:
297.16451.
({(1Z)-3-[(Benzyloxy)methyl]-2,2-dimethylcyclopro-
pylidene}(2H)methyl}trimethylsilane (2′)
Prepared by gold-catalyzed rearrangement of 1b′ and purified by
flash column chromatography (petroleum ether/EtOAc, 98:2 to 96:4)
to give a colorless oil; yield: 60 mg (89%).
IR (neat): 1726, 1454, 1365, 1245, 1090, 1051, 1028, 834, 755, 734,
695 cm–1
.
Reactions involving air- and moisture-sensitive organometallic re-
agents were carried out under argon in flame-dried glassware with a
magnetic stirring bar and sealed with a rubber septum. THF was dis-
tilled from Na-benzophenone. i-Pr2NH, i-Pr2NEt, CH2Cl2, and i-PrOH
were distilled from CaH2. Reagents were obtained from commercial
suppliers and used as received without further purification. Flash col-
umn chromatography was performed on silica gel (230–400 mesh). IR
spectra were recorded with a Bruker TENSOR 27 instrument (IR-FT)
with attenuated total reflectance (ATR). NMR spectra were recorded
with a Bruker Avance 400 instrument. 1H NMR spectra were recorded
at 400 MHz relative to TMS. 13C NMR spectra were recorded at 100
1H NMR (400 MHz, CDCl3): δ = 7.37–7.27 (m, 5 H), 4.56 (d, AB syst, J =
12.0 Hz, 1 H), 4.51 (d, AB syst, J = 12.0 Hz, 1 H), 3.64 (dd, J = 10.7, 5.6
Hz, 1 H), 3.34 (dd, J = 10.6, 9.2 Hz, 1 H), 1.47 (dd, J = 9.1, 5.6 Hz, 1 H),
1.24 (s, 3 H), 1.17 (s, 3 H), 0.09 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 154.5 (C), 138.8 (C), 128.5 (2 CH),
127.9 (2 CH), 127.6 (CH), 116.5 (CD, t, 1JC-D = 21.2 Hz), 72.6 (CH2), 69.5
(CH2), 27.1 (CH3), 26.5 (CH), 20.8 (C), 19.5 (CH3), –0.5 (3 CH3).
HRMS (ESI): m/z [M + Na+] calcd for C17H25DONaSi: 298.17092; found:
298.17079.
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Synthesis
{2-[2-(Benzyloxy)-1-(methoxymethoxy)ethyl]-3,3-dimethylcyclo-
prop-1-en-1-yl}dimethylphenylsilane (9a); Typical Procedures
{[(1Z)-3-(Benzyloxymethyl)-2,2-dimethylcyclopropylidene]meth-
yl}dimethylphenylsilane (10a); Typical Procedure for Gold-Cata-
lyzed Rearrangement of 9a–j/9j′
2-(Benzyloxy)-1-[2-(dimethylphenylsilyl)-3,3-dimethylcycloprop-
1-en-1-yl]ethan-1-ol (8a)
To a solution of silylcyclopropene 9a (400 mg, 1.01 mmol) in CH2Cl2 at
r.t., was added AuCl (11.7 mg, 0.0503 mmol, 5 mol%). The mixture
was stirred for 8 h, and then it was filtered through Celite (CH2Cl2).
The filtrate was evaporated under reduced pressure and the crude
material was analyzed by 1H NMR spectroscopy, which indicated the
formation of 10a as a single detectable geometric isomer (Z/E >96:4).
After purification by flash column chromatography (petroleum
ether/Et2O, 95:5), 10a (292 mg, 86%) was isolated as a yellow oil.
To a solution of cyclopropenylsilane 6 (1.29 g, 6.39 mmol, 1.6 equiv)
in THF (20 mL) at –78 °C was added dropwise 2.5 M n-BuLi in hexanes
(2.4 mL, 6.0 mmol, 1.5 equiv). The mixture was stirred for 1 h with
the temperature rising from –78 °C to –10 °C, the mixture was cooled
to –50 °C and (benzyloxy)acetaldehyde (561 μL, 4.00 mmol) was add-
ed. The mixture was allowed to warm to –10 °C over 1 h, stirred for a
further 1 h at this temperature and then hydrolyzed with sat. aq NH4Cl
soln. The layers were separated and the aqueous phase was extracted
with Et2O. The combined organic phases were washed with brine,
dried (MgSO4), filtered, and concentrated under reduced pressure. Pu-
rification of the crude material by flash column chromatography (pe-
troleum ether/Et2O, 100:0 to 93:7) afforded alcohol 8a (977 mg, 70%)
as a yellow oil.
IR (neat): 1726, 1454, 1427, 1365, 1246, 1113, 1089, 1074, 840, 827,
730, 696 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.55–7.50 (m, 2 H), 7.36–7.27 (m, 8 H),
5.99 (d, J = 1.7 Hz, 1 H), 4.55 (d, AB syst, J = 12.0 Hz, 1 H), 4.50 (d, AB
syst, J = 12.0 Hz, 1 H), 3.64 (dd, J = 10.6, 5.7 Hz, 1 H), 3.35 (dd, J = 10.6,
9.1 Hz, 1 H), 1.50 (ddd, J = 9.1, 5.7, 1.7 Hz, 1 H), 1.15 (s, 3 H), 1.08 (s,
3 H), 0.36 (s, 6 H).
IR (neat): 3448 (br), 1777, 1454, 1428, 1363, 1248, 1113, 818, 778,
13C NMR (100 MHz, CDCl3): δ = 156.6 (C), 139.4 (C), 138.7 (C), 134.0
(2 CH), 129.0 (CH), 128.5 (2 CH), 127.9 (4 CH), 127.7 (CH), 115.0 (CH),
72.6 (CH2), 69.5 (CH2), 27.4 (CH), 26.3 (CH3), 21.1 (C), 19.3 (CH3), –1.8
(2 CH3).
HRMS (ESI): m/z [M + Na+] calcd for C22H28OSiNa: 359.18016.; found:
359.18051.
731, 697, 655 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.58–7.55 (m, 2 H), 7.40–7.27 (m, 8 H),
4.91 (m, 1 H), 4.56 (d, AB syst, J = 12.1 Hz, 1 H), 4.53 (d, AB syst, J =
12.1 Hz, 1 H), 3.63 (dd, J = 9.6, 3.5 Hz, 1 H), 3.49 (dd, J = 9.6, 6.9 Hz,
1 H), 2.24 (d, J = 5.1 Hz, 1 H, OH), 1.18 (s, 3 H), 1.17 (s, 3 H), 0.424 (s,
3 H), 0.419 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 149.0 (C), 138.1 (C), 138.0 (C), 133.8
(2 CH), 129.4 (CH), 128.6 (2 CH), 128.0 (2 CH), 127.9 (3 CH), 124.6 (C),
73.6 (CH2), 73.2 (CH2), 69.8 (CH), 27.93 (CH3), 27.85 (CH3), 22.6 (C),
–1.6 (2 CH3).
HRMS (ESI): m/z [M + Na+] calcd for C22H28O2SiNa: 375.17508; found:
375.17532.
tert-Butyl({3-[(3Z)-3-[(dimethylphenylsilyl)methylidene]-2,2-di-
methylcyclopropyl]}propoxy)dimethylsilane (10b)
Purified by flash column chromatography (petroleum ether/Et2O,
98:2) to give a yellow oil; yield: 144 mg (74%).
IR (neat): 1723, 1471, 1462, 1428, 1247, 1111, 1098, 832, 773, 728,
698, 663 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.56–7.51 (m, 2 H), 7.36–7.33 (m, 3 H),
5.95 (d, J = 1.5 Hz, 1 H), 3.67–3.58 (m, 2 H), 1.67–1.60 (m, 2 H), 1.48–
1.32 (m, 2 H), 1.10 (s, 3 H), 1.05–1.01 (m, 1 H), 1.01 (s, 3 H), 0.89 (s,
9 H), 0.35 (s, 6 H), 0.05 (s, 6 H).
13C NMR (100 MHz, CDCl3): δ = 160.9 (C), 139.9 (C), 134.0 (2 CH),
128.9 (CH), 127.8 (2 CH), 112.9 (CH), 63.2 (CH2), 33.3 (CH2), 27.4
(CH3), 26.7 (CH3), 26.1 (3 CH3), 24.7 (CH2), 20.1 (C), 19.2 (CH), 18.5 (C),
–1.7 (2 CH3), –5.1 (2 CH3).
{2-[2-(Benzyloxy)-1-(methoxymethoxy)ethyl]-3,3-dimethylcyclo-
prop-1-en-1-yl}dimethylphenylsilane (9a)
To a solution of alcohol 8a (507 mg, 1.44 mmol) in CH2Cl2 (15 mL) at
0 °C were successively added i-Pr2NEt (1.25 mL, 7.18 mmol, 5 equiv)
and MOMCl (0.55 mL, 7.2 mmol, 5 equiv) dropwise. The mixture was
stirred for 12 h at r.t., and then it was hydrolyzed with sat. aq NH4Cl
soln. The layers were separated and the aqueous phase was extracted
with CH2Cl2. The combined organic phases were washed with brine,
dried (MgSO4), filtered, and concentrated under reduced pressure.
The crude material was purified by flash column chromatography
(petroleum ether/Et2O, 90:10) to afford 9a (508 mg, 89%) as a yellow
oil.
HRMS (ESI): m/z [M + H+] calcd for C23H41OSi2: 389.26905; found:
389.26915.
{[(1Z)-2,2-Dimethyl-3-(2-phenylethyl)cyclopropylidene]meth-
yl}dimethylphenylsilane (10c)
IR (neat): 1776, 1364, 1248, 1153, 1113, 1028, 919, 817, 778, 731,
697, 655 cm–1
.
Purified by flash column chromatography (petroleum ether/Et2O,
98:2) to give a colorless oil; yield: 66 mg (78%).
1H NMR (400 MHz, CDCl3): δ = 7.56–7.53 (m, 2 H), 7.36–7.25 (m, 8 H),
4.98 (app t, J = 5.6 Hz, 1 H), 4.72 (d, AB syst, J = 6.6 Hz, 1 H), 4.61 (d, AB
syst, J = 6.6 Hz, 1 H), 4.57 (d, AB syst, J = 12.0 Hz, 1 H), 4.53 (d, AB syst,
J = 12.0 Hz, 1 H), 3.62 (d, J = 5.6 Hz, 2 H), 3.38 (s, 3 H), 1.153 (s, 3 H),
1.148 (s, 3 H), 0.41 (s, 6 H).
13C NMR (100 MHz, CDCl3): δ = 146.9 (C), 138.3 (C), 137.9 (C), 133.9
(2 CH), 129.3 (CH), 128.4 (2 CH), 127.9 (3 CH), 127.7 (2 CH), 125.3 (C),
94.7 (CH2), 73.4 (CH2), 72.5 (CH), 72.2 (CH2), 55.5 (CH3), 27.92 (CH3),
27.90 (CH3), 21.6 (C), –1.6 (2 CH3).
IR (neat): 1722, 1495, 1454, 1427, 1367, 1245, 1113, 841, 826, 788,
746, 729, 697 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.57–7.54 (m, 2 H), 7.39–7.35 (m, 3 H),
7.32–7.27 (m, 2 H), 7.23–7.18 (m, 3 H), 5.91 (br s, 1 H), 2.74 (br t, J =
7.5 Hz, 2 H), 1.75–1.68 (m, 2 H), 1.11 (s, 3 H), 1.11–1.07 (m, 1 H), 0.99
(s, 3 H), 0.37 (s, 6 H).
13C NMR (100 MHz, CDCl3): δ = 160.5 (C), 142.6 (C), 139.8 (C), 134.0
(2 CH), 128.9 (CH), 128.7 (2 CH), 128.4 (2 CH), 127.8 (2 CH), 125.8
(CH), 113.1 (CH), 36.4 (CH2), 30.6 (CH2), 27.2 (CH), 26.6 (CH3), 20.3 (C),
19.2 (CH3), –1.7 (2 CH3).
HRMS (ESI): m/z [M + Na+] calcd for C24H32O3SiNa: 419.20129; found:
419.20175.
HRMS (ESI): m/z [M + Na+] calcd for C22H28SiNa: 343.18525; found:
343.18531.
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Synthesis
{[(1Z)-2,2-Dimethyl-3-(pent-4-en-1-yl)cyclopropylidene]meth-
yl}dimethylphenylsilane (10d)
13C NMR (100 MHz, CDCl3): δ = 163.2 (C, 1JC-F = 245.3 Hz, C7), 155.6 (C),
3
139.3 (C), 134.0 (2 CH), 129.9 (CH, JC-F = 4.2 Hz), 129.1 (CH), 127.9
(2 CH), 127.5 (CH, 3JC-F = 7.8 Hz), 125.9 (C, 2J = 15.8 Hz), 123.6 (CH,
Purified by flash column chromatography (petroleum ether/Et2O,
95:5) to give a colorless oil; yield: 61 mg (74%).
2
4JC-F = 3.3 Hz), 117.8 (CH), 114.8 (CH, JC-F = 21.9 Hz), 26.2 (CH), 24.3
(C), 19.3 (2 CH3), –1.7 (CH3), –1.8 (CH3).
IR (neat): 1722, 1641, 1428, 1368, 1246, 1113, 910, 840, 825, 787,
729, 698 cm–1
.
{[(1Z)-2,2-Dimethyl-3-(propan-2-yl)cyclopropylidene]methyl}di-
methylphenylsilane (10i)
1H NMR (400 MHz, CDCl3): δ = 7.59–7.55 (m, 2 H), 7.39–7.35 (m, 3 H),
5.99 (d, J = 1.0 Hz, 1 H), 5.85 (ddt, J = 17.0, 10.2, 6.6 Hz, 1 H), 5.04 (dm,
app br d, J = 17.0 Hz, 1 H), 4.97 (dm, app br d, J = 10.5 Hz, 1 H), 2.14–
2.08 (m, 2 H), 1.58–1.33 (m, 4 H), 1.13 (s, 3 H), 1.08–1.06 (m, 1 H),
1.06 (s, 3 H), 0.39 (s, 6 H).
13C NMR (100 MHz, CDCl3): δ = 161.0 (C), 139.9 (C), 139.2 (CH), 134.0
(2 CH), 128.9 (CH), 127.8 (2 CH), 114.5 (CH2), 112.0 (CH), 33.8 (CH2),
29.4 (CH2), 28.0 (CH2), 27.6 (CH), 26.7 (CH3), 20.1 (C), 19.3 (CH3), –1.7
(2 CH3).
Purified by flash column chromatography (petroleum ether) to give a
colorless oil; yield: 18 mg (90%).
IR (neat): 1720, 1463, 1427, 1368, 1289, 1246, 1176, 1113, 970, 840,
822, 794, 767, 728, 698 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.57–7.53 (m, 2 H), 7.37–7.34 (m, 3 H),
5.99 (d, J = 1.7 Hz, 1 H), 1.36–1.30 (m, 1 H), 1.11 (s, 3 H), 1.06 (s, 3 H),
1.02 (d, J = 6.6 Hz, 3 H), 0.99 (d, J = 6.6 Hz, 3 H), 0.81 (dd, J = 10.2, 1.7
Hz, 1 H), 0.36 (s, 6 H).
(4-{(3Z)-3-[(Dimethylphenylsilyl)methylene]-2,2-dimethylcyclo-
propyl}but-1-yn-1-yl)trimethylsilane (10e)
13C NMR (100 MHz, CDCl3): δ = 160.9 (C), 139.9 (C), 134.0 (2 CH),
128.9 (CH), 127.8 (2 CH), 112.5 (CH), 35.6 (CH), 29.3 (CH), 26.9 (CH3),
23.4 (CH3), 23.1 (CH3), 20.4 (C), 19.3 (CH3), –1.7 (2 CH3).
Purified by flash column chromatography (petroleum ether/Et2O,
90:10) to give a colorless oil; yield: 73 mg (86%).
({(3R*/S*)-(1Z)-2,2-Dimethyl-3-[(1R*)-1-phenylethyl]cyclopro-
pylidene}methyl)dimethylphenylsilane (10j/10j′)
IR (neat): 2174, 1723, 1247, 1113, 1047, 838, 759, 729, 698, 638 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.57–7.53 (m, 2 H), 7.38–7.35 (m, 3 H),
6.02 (d, J = 1.7 Hz, 1 H), 2.36–2.32 (m, 2 H), 1.70–1.56 (m, 2 H), 1.17–
1.13 (m, 1 H), 1.13 (s, 3 H), 1.05 (s, 3 H), 0.38 (s, 6 H), 0.17 (s, 9 H).
13C NMR (100 MHz, CDCl3): δ = 159.9 (C), 139.7 (C), 134.0 (2 CH),
129.0 (CH), 127.8 (2 CH), 113.6 (CH), 107.6 (C), 84.2 (C), 27.9 (CH2),
27.0 (CH), 26.5 (CH3), 20.5 (C), 20.5 (CH2), 19.4 (CH3), 0.3 (3 CH3), –1.7
(2 CH3).
The gold-catalyzed rearrangement of a diastereomeric mixture of
9j/9j′ (90:10) afforded a mixture of 10j/10j′ (34 mg, 81%, 65:35). Al-
ternatively, the gold-catalyzed rearrangement of a diasteromeric mix-
ture of 9j/9j′ (23:77) produced a diastereomeric mixture of 10j/10j′
(13 mg, 77%, 43:57).
IR (neat): 1723, 1602, 1494, 1450, 1427, 1246, 1112, 968, 841, 827,
786, 729, 697 cm–1
.
HRMS (ESI): m/z [M + Na+] calcd for C21H32Si2Na: 363.19347; found:
363.19347.
Diastereomer 10j
1H NMR (400 MHz, CDCl3): δ = 7.59–7.57 (m, 2 H), 7.38–7.17 (m, 8 H),
6.13 (d, J = 1.3 Hz, 1 H), 2.55–2.43 (m, 1 H), 1.41–1.37 (m, 1 H), 1.37
(d, J = 6.9 Hz, 3 H), 1.11 (s, 3 H), 0.94 (s, 3 H), 0.39 (s, 6 H).
13C NMR (100 MHz, CDCl3): δ = 159.9 (C), 147.8 (C), 139.7 (C), 134.0
(2 CH), 129.0 (CH), 128.4 (2 CH), 127.9 (2 CH), 126.8 (2 CH), 125.9
(CH), 113.3 (CH), 39.9 (CH), 33.5 (CH), 26.5 (CH3), 23.7 (CH3), 21.0 (C),
19.6 (CH3), –1.7 (2 CH3).
{[(1Z)-2,2-Dimethyl-3-phenylcyclopropylidene]methyl}dimethyl-
phenylsilane (10f)
Purified by flash column chromatography (toluene) to give a yellow
oil; yield: 20 mg (49%).
IR (neat): 1733, 1601, 1494, 1449, 1427, 1246, 1113, 964, 839, 816,
793, 730, 697 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.62–7.59 (m, 2 H), 7.39–7.37 (m, 3 H),
7.28–7.25 (m, 2 H), 7.19–7.16 (m, 3 H), 6.29 (d, J = 1.6 Hz, 1 H), 2.41
(d, J = 1.6 Hz, 1 H), 1.28 (s, 3 H), 0.79 (s, 3 H), 0.44 (s, 6 H).
13C NMR (100 MHz, CDCl3): δ = 156.9 (C), 139.4 (C), 138.7 (C), 134.0
(2 CH), 129.13 (2 CH), 129.10 (CH), 128.1 (2 CH), 127.9 (2 CH), 125.9
(CH), 117.1 (CH), 32.6 (CH), 26.7 (CH3), 24.5 (C), 19.1 (CH3), –1.6 (CH3),
–1.7 (CH3).
Diastereomer 10j′
1H NMR (400 MHz, CDCl3): δ = 7.53–7.48 (m, 2 H), 7.38–7.17 (m, 8 H),
5.70 (br s, 1 H), 2.54–2.43 (m, 1 H), 1.36 (d, J = 6.9 Hz, 3 H), 1.28 (m,
1 H), 1.17 (s, 6 H), 0.334 (s, 3 H), 0.329 (s, 3 H).
13C NMR (100 MHz, CDCl3): δ = 159.1 (C), 147.1 (C), 139.8 (C), 134.0
(2 CH), 128.9 (CH), 128.4 (2 CH), 127.8 (2 CH), 127.3 (2 CH), 125.9
(CH), 113.4 (CH), 39.8 (CH), 34.3 (CH), 26.9 (CH3), 22.5 (CH3), 20.4 (C),
19.3 (CH3), –1.7 (2 CH3).
{[(1Z)-3-(2-Fluorophenyl)-2,2-dimethylcyclopropylidene]meth-
yl}dimethylphenylsilane (10h)
HRMS (ESI): m/z [M + Na+] calcd for C22H28SiNa: 343.18525; found:
343.18529.
Purified by flash column chromatography (petroleum ether/Et2O,
90:10) to give a colorless oil; yield: 30 mg (36%).
IR (neat): 1732, 1581, 1489, 1454, 1246, 1220, 1234, 1113, 1098, 965,
Preparation and Gold-Catalyzed Rearrangement of (R)-9a
829, 814, 789, 753, 730, 698 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.61–7.57 (m, 2 H), 7.39–7.36 (m, 3 H),
7.18–7.13 (m, 1 H), 7.08 (m, 1 H), 7.04–6.99 (m, 2 H), 6.32 (d, J = 1.8
Hz, 1 H), 2.45 (m, app br s, 1 H), 1.31 (s, 3 H), 0.78 (s, 3 H), 0.43 (s,
6 H).
2-(Benzyloxy)-1-[2-(dimethylphenylsilyl)-3,3-dimethylcycloprop-
1-en-1-yl]ethanone (11)
To a solution of (±)-8a (56.9 mg, 0.161 mmol) in CH2Cl2 (2 mL) at 0 °C,
was added Dess–Martin periodinane (82.2 mg, 0.194 mmol, 1.2
equiv). After 10 min at 0 °C, the mixture was warmed to r.t., stirred for
further 10 min and then hydrolyzed with sat. aq NaHCO3 soln. The re-
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sulting mixture was extracted with Et2O and the combined organic
phases were washed with brine, dried (Na2SO4), filtered, and concen-
trated under reduced pressure. The crude material was purified by
flash column chromatography (petroleum ether/Et2O, 80:20) to afford
11 (52.7 mg, 93%) as a yellow oil.
IR (neat): 1471, 1462, 1249, 1111, 1098, 833, 773, 726, 698, 661 cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.55–5.51 (m, 2 H), 7.37–7.35 (m, 3 H),
3.60 (t, J = 6.7 Hz, 2 H), 1.59–1.50 (m, 2 H), 1.26–1.15 (m, 2 H), 0.98 (s,
3 H), 0.90 (s, 9 H), 0.80 (s, 3 H), 0.72 (dd, J = 14.8, 5.0 Hz, 1 H), 0.57 (dd,
J = 14.8, 8.6 Hz, 1 H), 0.47 (app td, J = 8.6, 5.0 Hz, 1 H), 0.36 (ddd, J =
8.6, 7.7, 6.5 Hz, 1 H), 0.302 (s, 3 H), 0.298 (s, 3 H), 0.06 (s, 6 H).
13C NMR (100 MHz, CDCl3): δ = 139.8 (C), 133.8 (2 CH), 128.9 (CH),
127.8 (2 CH), 63.5 (CH2), 33.4 (CH2), 29.4 (CH3), 26.8 (CH), 26.1
(3 CH3), 21.9 (CH), 20.8 (CH2), 18.5 (C), 17.2 (C), 15.0 (CH3), 9.9
(CH2), –2.8 (CH3), –2.9 (CH3), –5.1 (2 CH3).
IR (neat): 1736, 1687, 1250, 1113, 1078, 835, 817, 780, 733, 697, 655
cm–1
.
1H NMR (400 MHz, CDCl3): δ = 7.54–7.52 (m, 2 H), 7.41–7.30 (m, 8 H),
4.55 (s, 2 H), 4.18 (s, 2 H), 1.25 (s, 6 H), 0.49 (s, 6 H).
13C NMR (100 MHz, CDCl3): δ = 192.1 (C), 148.0 (C), 143.4 (C), 137.4
(C), 135.8 (C), 133.8 (2 CH), 130.0 (CH), 128.6 (2 CH), 128.3 (2 CH),
128.2 (2 CH), 128.1 (CH), 74.2 (CH2), 73.3 (CH2), 27.2 (2 CH3), 24.8 (C),
–2.4 (2 CH3).
HRMS (ESI): m/z [M + H+] calcd for C23H43OSi2: 391.28470; found:
391.28444.
HRMS (ESI): m/z [M + Na+] calcd for C22H26OSiNa: 373.15943; found:
373.15948.
Acknowledgment
One of us (A.A.) thanks the MNSER for a Ph.D. grant.
(R)-2-(Benzyloxy)-1-[2-(dimethylphenylsilyl)-3,3-dimethylcyclo-
prop-1-en-1-yl]ethan-1-ol [(R)-8a]
To a solution of ketone 11 (51.4 mg, 0.147 mmol) in i-PrOH (3 mL) at
r.t., was added catalyst (R,R)-[Ru]-I26 (50 μL, 0.17 M stock solution in
CH2Cl2, 0.0085 mmol, 6 mol%). After 15 h at r.t., more catalyst (R,R)-
[Ru]-I (6 mol%) was added. After 4 h at r.t., the reaction was still in-
complete and another portion of catalyst (R,R)-[Ru]-I (6 mol%) was
added. The mixture was heated at 40 °C for 2 h, then cooled to r.t. and
concentrated under reduced pressure. The residue was purified by
flash column chromatography (petroleum ether/Et2O, 80:20) to afford
optically active alcohol (R)-8a (38.4 mg, 74%) as a colorless oil.
Supporting Information
Supporting information for this article is available online at
http://dx.doi.org/10.1055/s-0035-1561486.
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References
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Gold-Catalyzed Rearrangement of (R)-9a
The rearrangement of optically active (R)-9a (75% ee) catalyzed by
AuCl (5 mol%) (CH2Cl2, r.t., 8 h) provided (silylmethylene)cyclopro-
pane 10a (23 mg, 95%) as a racemate (0% ee).
The enantiomeric excess of this latter product was determined by SFC
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220 nm] after calibration with an authentic sample of (±)-10a arising
from the gold-catalyzed rearrangement of (±)-9a: tR = 2.99, 3.85 min,
see Supporting Information.
{(1R*,3S*)-3-[3-(tert-Butyldimethylsiloxy)propyl]-2,2-dimethylcy-
clopropylmethyl}dimethylphenylsilane (12)
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and the filtrate was evaporated under reduced pressure. The residue
was purified by flash column chromatography (petroleum ether/EtOAc,
90:10) to provide 12 (27 mg, 88%, dr > 95:5) as a colorless oil. The rel-
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constant value between the two cyclopropyl protons (J = 8.6 Hz).
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© Georg Thieme Verlag Stuttgart · New York — Synthesis 2016, 48, 3165–3174