A direct synthesis of alkenyl alkylidene bicyclo[3.1.0]hexane derivatives via ruthenium(ii)-catalysed bicyclisation of allenynes

Article abstract of DOI:10.1055/s-2008-1032015

The reaction of allenynes with N₂CHSiMe₃ in the presence of RuCl(cod)Cp* catalyst at room temperature constitutes a selective, general route to alkylidenebicyclo[3.1.0]hexanes having an adjacent Z-CH=CHSiMe₃ group. The reaction shows that the RuCl(Cp*) moiety favours reductive elimination of a metallacyclobutane intermediate and not the enyne metathesis process. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2008-1032015

LETTER
193
A Direct Synthesis of Alkenyl Alkylidene Bicyclo[3.1.0]hexane Derivatives via
Ruthenium(II)-Catalysed Bicyclisation of Allenynes
Synthesis of
A
lke
h
nyl
A
lkylide
l
ne Bic
o
yclo[3.1.0]
h
é
D
erivativesVovard-Le Bray,a Sylvie Dérien,a Pierre H. Dixneuf,*a Masahiro Murakami*b
a
Laboratoire ‘catalyse et organométalliques’, Institut Sciences Chimiques de Rennes, UMR 6226 CNRS Université de Rennes 1,
Campus de Beaulieu, 35042 Rennes, France
Fax +33(223)236939; E-mail: pierre.dixneuf@univ-rennes1.fr
Department of Synthetic Chemistry and Biological Chemistry, Kyoto University, Katsura, Kyoto 615-8510, Japan
b
Received 26 October 2007
Dedicated to the late Professor Yoshihiko Ito for his outstanding contribution to catalysis and synthesis
fer an entry to bicyclic alkylidenecyclopropanes I by
Abstract: The reaction of allenynes with N2CHSiMe3 in the pres-
ence of RuCl(cod)Cp* catalyst at room temperature constitutes a se-
lective, general route to alkylidenebicyclo[3.1.0]hexanes having an
adjacent Z-CH=CHSiMe3 group. The reaction shows that the
activation of allenynes on the condition that the possible
enyne metathesis product (II) formation23 could be inhib-
ited (Scheme 1). However, the catalytic transformation of
RuCl(Cp*) moiety favours reductive elimination of a metallacy- allenynes raises questions about the regioselectivity of
clobutane intermediate and not the enyne metathesis process.
initial interaction of allene C=C bond with a carbene
Ru=C bond that can not be predicted. The reaction of al-
lenes with electrophilic alkenes promoted by
RuCl(cod)Cp complex has shown that the internal double
bond is involved in the oxidative coupling,24 whereas
RuCl(cod)Cp*, with sterically hindered allenylboronates,
promoted the [2+2] cycloaddition of only the terminal al-
lene C=CH2 bond.25
Keywords: allenynes, C–C coupling cyclisation, homogeneous ca-
talysis, ruthenium
Methylenecyclopropanes play a key role in the construc-
tion of 5-membered cycles, via initial metal-catalysed
opening of the cyclopropane moiety, thus offering a three-
carbon component for cycloaddition with unsaturated
molecules.1,2 Initial works have shown that palladium(0)-
and nickel(0)-catalysed activation of methylenecyclopro-
panes leads to the formation of alkylidenecyclopentanes3,4
or 5-membered heterocycles.5,6 Methylenecyclopropanes
are now offering applications for hydrocarbonation,7,8 co-
balt-catalysed carbonylation9 and hydroamination.10,11
There is a renaissance of alkylidenecyclopropanes in syn-
thesis via their skeleton rearrangements to build small cy-
cles,12 the formation of alkylidene cyclopentanones via
nickel(0)-catalysed cycloaddition with alkenyl metal car-
benes,13 and especially their rearrangement into cy-
clobutenes catalysed by palladium(II)14 or PtCl2.15
Y
R'
R
Ru = CHY
R'
A
A
R
I
R'
M = CHY
R
.
×
R
R
metathesis23
A
R
II
A = NTs, C(CO2Me)2
Scheme 1
The above recent applications motivate the search for easy
functional methylenecyclopropane syntheses. Simple
methylenecyclopropanes can be prepared by two main
routes.1 The first one involves the cyclopropane ring for-
mation by carbene addition to unsaturated compounds
such as allenes and olefins,16 or by elimination reactions.17
The second route involves the synthesis of methylenecy-
clopropanes from cyclopropane substrates, with subse-
quent formation of a double bond,18 including double
bond shift reactions19 and Wittig olefination.20
Herein we report that the RuCl(cod)Cp* catalyst precur-
sor in the presence of N2CHSiMe3 does not promote the
coupling with terminal allene bond, but the regioselective
transformation of allenynes into the new alkylidenebicyc-
lo[3.1.0]hexane derivatives of type I containing an adja-
cent Z-alkenyl group. From the synthetic point of view,
the products I are of high interest due to the reactivity of
the cyclopropane ring which is expected to be enhanced
by simultaneous substitution with alkylidene and alkenyl
groups.
Recently, the selective transformation of enynes into alk-
enylbicyclo[3.1.0]hexane derivatives has been promoted
by ruthenium(II) catalyst on reaction with diazoal-
kanes.21,22 We then reasoned that such a reaction could of-
The reaction of allenyne 1a with N2CHSiMe3 (1.1 equiv)
in Et2O with RuCl(cod)Cp* (8 mol%) for one hour at
room temperature led to 85% conversion of 1a and to the
formation of 2a, isolated in 52% yield (Table 1). The al-
lenynes 1b–d, bearing
a
nitrogen linkage with
N2CHSiMe3 (1.1 equiv, 2 M in Et2O), reacted with
RuCl(cod)Cp* (8 mol%) in Et2O at room temperature and
led to products 2b–d, isolated after purification by silica
gel chromatography (Table 1).26
SYNLETT 2008, No. 2, pp 0193–0196
Advanced online publication: 04.01.2008
DOI: 10.1055/s-2008-1032015; Art ID: G36007ST
© Georg Thieme Verlag Stuttgart · New York
x
x.
x
x.
2
0
0
8

194
C. Vovard-Le Bray et al.
LETTER
MeO2C
MeO2C
Table 1
Me3Si
MeO2C
RuCl(cod)Cp*
(8 mol%)
TsN
Me3Si
TsN
r.t., 16 h
MeO2C
6 52% (100% conv.)
RuCl(cod)Cp*
(8 mol%)
5
R1
R2
R1
+
R2
r.t.
1
N2CHSiMe3
+
2
Scheme 3
N2CHSiMe3
Entry
R1
R2
Time (h) Conv. (%) Yield (%)
(b) The opening of the ruthenacyclobutene A can then af-
ford intermediate B. The A → B transformation leads to
the Z configuration of the alkenyl group. This stereoselec-
tivity may result from intramolecular Cl–SiMe3 bond in-
teraction in the intermediate A.
a
b
c
Me
Me
Et
1
19
10
6
85
100
100
95
52
71
85
40
Me
i-Pr
i-Pr
(c) The trapping of the allene internal C=C bond by the
Ru=C bond and [2+2] addition is expected to lead to the
metallacyclobutane C.
d
-(CH2)5-
Whereas 1a reached 85% conversion after one hour, the
conversion of 1b and 1c containing bulkier R1 and R2
groups was complete only after 19 hours and 10 hours and
the corresponding products 2b (two isomers, 55:45) and
2c were obtained in 71% and 85% isolated yields, respec-
tively. However, 1d reached 95% conversion after six
hours, though 2d was isolated in only 40% yield.26 For all
derivatives 2a–d the Z-configuration of the alkenyl group
was observed. Thus, this reaction shows high regioselec-
tivity of the interaction of the allene internal C=C bond
with the catalyst.
(d) The last step leads to the cyclopropane formation thus
affording the alkylidene bicyclo[3.1.0]hexane derivative.
Indeed, DFT calculations show that the [Ru(Cl)(Cp*)]
unit, inside a metallacyclobutane moiety, with an adjacent
vinyl group, favours reductive elimination rather than a
metathesis process (retro-[2+2] addition),22 by the initial
coordination of the vinyl group leading to the alkyl allyl
ruthenium intermediate of type D.
The allenynes 3 containing the dimethylallene function
and an aryl group at the alkyne C(1) [3a (Ar = Ph), 3b
(Ar = p-MeOC6H4)] reacted as previously for 16 hours at
room temperature.26 The alkenyl alkylidene bicyc-
lo[3.1.0]hexane derivatives were formed in modest con-
version and yield for 4a (35%) (Scheme 2). At room
temperature 3b gave a convenient conversion (76%) and
isolated yield (56%) of 4b.
Cl
Y
Y
[Ru]
Ru
R1
R1
[Ru]
(a)
R2
1, 3, 5
R2
(b)
A
A
A
B
(c)
Y = SiMe3
[Ru] = RuClCp*
R1
R1
R2
R2
A = NTs, C(CO2Me)2
Y
Ar
Y
[Ru]
[Ru]
Me3Si
TsN
Ar
2, 4, 6
(d)
RuCl(cod)Cp*
(8 mol%)
TsN
A
C
A
D
16 h, r.t.
4
3
Scheme 4
+
N2CHSiMe3
4a Ar = Ph 35% (50% conv.)
4b Ar = 4-MeOC6H4 56% (76% conv.)
The above results show a novel access to alkylidenebicy-
clo[3.1.0]hexanes with a neighbouring Z-alkenyl group. It
appears to be the most direct route to bicyclic compounds
containing a reactive alkylidenecyclopropane unit. The
formed molecules offer potential for catalytic access to 5-
to 8-membered cycles enhanced by the simultaneous pres-
ence of a vinyl cyclopropyl unit.27 The described reaction
also demonstrates that the Cp*(Cl)Ru moiety, inside a
metallacyclobutane intermediate, resulting from Ru=C
and C=C bond addition, favours reductive elimination and
inhibits retro-[2+2] addition such as an alkene metathesis
process. This phenomenon deserves to be explored and is
expected to give a new life to ruthenium carbenes in catal-
ysis.
Scheme 2
Under similar conditions the allenyne 5 with a carbon
bridge between the allene and yne functions led to com-
pound 6 in 52% yield (Scheme 3).26
On the basis of the above results, a catalytic cycle can be
proposed (Scheme 4).
(a) The generation of the [Cp*(Cl)Ru=CHSiMe3] moiety
and its [2+2] cycloaddition with the alkyne bond is ex-
pected to afford the intermediate A. Simple models show
that steric interactions allow this [2+2] addition to take
place only with anti position of the Cp* and SiMe3 groups.
Synlett 2008, No. 2, 193–196 © Thieme Stuttgart · New York

LETTER
Synthesis of Alkenyl Alkylidene Bicyclo[3.1.0]hexane Derivatives
195
(20) (a) Bestmann, H.-J.; Denzel, T. Tetrahedron Lett. 1966,
Acknowledgment
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E. Tetrahedron Lett. 1988, 29, 2531. (d) Maercker, A.;
Daub, V. E. E. Tetrahedron 1994, 50, 2439.
The authors are grateful to Dr. T. Matsuda and S. Kadowaki for dis-
cussions and providing allenynes, CNRS and Ministère de la re-
cherche for support, the latter for a PhD grant to C.V., the European
Union through network IDECAT and the Institut Universitaire de
France for membership (P.H.D.).
(21) Monnier, F.; Castillo, D.; Dérien, S.; Toupet, L.; Dixneuf, P.
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Dérien, S.; Dixneuf, P. H.; Toupet, L.; Ienco, A.; Mealli, C.
J. Am. Chem. Soc. 2007, 129, 6037.
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reaction was performed with a small substrate quantity (0.1
mmol) due to inefficient extraction techniques for small
quantities; for example, for 1c 40% and 85% isolated yields
were obtained from 0.1 mmol and 0.3 mmol, respectively.
Typical Procedure for the Catalytic Reaction: In a
Schlenk tube under an inert atmosphere, to a solution of the
allenyne in degassed Et2O (1.5 mL) was added the
(trimethylsilyl)diazomethane solution (2.0 M; 1.1 equiv) in
Et2O. Next, the precatalyst RuCl(cod)Cp* (8 mol%) was
introduced. The mixture was stirred at r.t. Reaction
completion was monitored using TLC or 1H NMR
techniques. The products were obtained after purification by
silica gel chromatography with an Et2O–pentane eluting
mixture.
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Data for compounds 2a–d, 4a,b, and 6:
Compound 2a: 1H NMR (300.13 MHz, CDCl3): d = 0.12 (s,
9 H, SiMe3), 1.68 (s, 3 H, Me), 1.69 (s, 3 H, Me), 1.95 (m, 1
H, CH), 2.45 (s, 3 H, Me), 3.26 (dd, J = 4.1, 9.4 Hz, 1 H,
NCH2), 3.27 (d, J = 9.0 Hz, 1 H, NCH2), 3.64 (d, J = 9.4 Hz,
1 H, NCH2), 3.80 (d, J = 9.1 Hz, 1 H, NCH2), 5.49 (d, J =
15.6 Hz, 1 H, =CHSiMe3), 6.02 (d, J = 15.6 Hz, 1 H, CH=),
7.32 (d, J = 7.8 Hz, 2 H, Ph), 7.67 (d, J = 8.2 Hz, 2 H, Ph).
13C NMR (75.47 MHz, CDCl3): d = 145.1, 143.3, 133.7,
129.5, 129.4, 127.6, 127.5, 122.3, 53.1, 50.0, 35.9, 29.9,
22.2, 21.6, 21.5, 0.8. HRMS: m/z calcd for C20H29NO2SiS:
375.1688; found: 375.1684.
Compound 2b (two isomers, 55:45): Major isomer: 1H NMR
(300.08 MHz, CDCl3): d = 0.11 (s, 9 H, SiMe3), 0.97 (t, J =
7.7 Hz, 3 H, Me), 1.70 (s, 3 H, Me), 1.91 (m, 1 H, CH), 1.99
(m, 2 H, CH2), 2.45 (s, 3 H, Me), 3.24 (m, 1 H, NCH2), 3.28
(d, J = 9.0 Hz, 1 H, NCH2), 3.65 (d, J = 9.2 Hz, 1 H, NCH2),
3.75 (d, J = 9.0 Hz, 1 H, NCH2), 5.47 (d, J = 15.6 Hz, 1 H,
=CHSiMe3), 6.01 (d, J = 15.6 Hz, 1 H, CH=), 7.32 (d, J = 7.9
Hz, 2 H, Ph), 7.68 (d, J = 8.2 Hz, 2 H, Ph). 13C NMR (75.47
MHz, CDCl3): d = 145.4, 143.3, 133.8, 133.0, 129.5, 129.2,
127.6, 121.2, 53.1, 50.5, 36.3, 30.5, 29.2, 21.5, 20.1, 12.0,
0.8. Minor isomer: 1H NMR (300.08 MHz, CDCl3): d = 0.13
(s, 9 H, SiMe3), 1.02 (t, J = 7.4 Hz, 3 H, Me), 1.62 (s, 3 H,
Me), 1.99 (m, 2 H, CH2), 2.01 (m, 1 H, CH), 2.45 (s, 3 H,
Me), 3.24 (m, 1 H, NCH2), 3.28 (d, J = 9.0 Hz, 1 H, NCH2),
3.63 (d, J = 9.1 Hz, 1 H, NCH2), 3.81 (d, J = 8.9 Hz, 1 H,
NCH2), 5.49 (d, J = 15.6 Hz, 1 H, =CHSiMe3), 6.00 (d, J =
15.5 Hz, 1 H, CH=), 7.32 (d, J = 7.9 Hz, 2 H, Ph), 7.68 (d,
J = 8.2 Hz, 2 H, Ph). 13C NMR (75.47 MHz, CDCl3): d =
145.8, 143.3, 133.2, 133.0, 129.5, 128.9, 127.6, 121.5, 53.4,
50.0, 36.3, 29.4, 28.7, 21.5, 20.5, 12.4, 0.8. HRMS: m/z
calcd for C21H31NO2SiS: 389.1845; found: 389.1854.
Compound 2c: 1H NMR (200.13 MHz, CDCl3): d = 0.11 (s,
9 H, SiMe3), 1.06 (m, 12 H, Me), 1.94 (m, 1 H, CH), 2.38 (m,
7430.
(15) Fürstner, A.; Aïssa, C. J. Am. Chem. Soc. 2006, 128, 6306.
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Chem. 1973, 1219. (b) Muthuramu, K.; Ramamurthy, V.
J. Chem. Soc., Chem. Commun. 1980, 243.
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J. Org. Chem. 1986, 51, 974. (b) Loosli, T.; Borer, M.;
Kulakowska, I.; Minger, A.; Neuenschwander, M.; Engel, P.
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Synlett 2008, No. 2, 193–196 © Thieme Stuttgart · New York

196
C. Vovard-Le Bray et al.
LETTER
2 H, CH), 2.44 (s, 3 H, Me), 3.19 (dd, J = 4.1, 8.8 Hz, 1 H,
NCH2), 3.25 (d, J = 8.3 Hz, 1 H, NCH2), 3.64 (d, J = 8.8 Hz,
1 H, NCH2), 3.72 (d, J = 8.5 Hz, 1 H, NCH2), 5.45 (d, J =
15.7 Hz, 1 H, =CHSiMe3), 5.94 (d, J = 15.7 Hz, 1 H, CH=),
7.32 (d, J = 7.7 Hz, 2 H, Ph), 7.70 (d, J = 8.1 Hz, 2 H, Ph).
13C NMR (75.47 MHz, CDCl3): d = 148.3, 146.9, 143.4,
133.7, 129.5, 127.7, 127.6, 119.0, 53.1, 50.5, 33.8, 33.6,
32.9, 28.5, 22.9, 22.6, 22.5, 22.2, 21.5, 1.0. HRMS: m/z
calcd for C24H37NO2SiS: 431.2314; found: 431.2304.
Compound 2d: 1H NMR (300.08 MHz, CDCl3): d = 0.12 (s,
9 H, SiMe3), 1.50 (m, 6 H, CH2), 1.98 (m, 1 H, CH), 2.07 (m,
4 H, CH2), 2.45 (s, 3 H, Me), 3.23 (dd, J = 4.1, 13.2 Hz, 1 H,
NCH2), 3.26 (d, J = 8.6 Hz, 1 H, NCH2), 3.61 (d, J = 9.2 Hz,
1 H, NCH2), 3.76 (d, J = 8.8 Hz, 1 H, NCH2), 5.48 (d, J =
15.6 Hz, 1 H, =CHSiMe3), 6.04 (d, J = 15.5 Hz, 1 H, CH=),
7.33 (d, J = 7.9 Hz, 2 H, Ph), 7.68 (d, J = 8.2 Hz, 2 H, Ph).
13C NMR (75.47 MHz, CDCl3): d = 145.5, 143.3, 135.3,
133.8, 129.6, 129.1, 127.6, 119.1, 53.2, 50.1, 47.5, 35.4,
33.2, 32.8, 29.3, 27.7, 26.4, 21.5, 0.8. HRMS: m/z calcd for
C23H33NO2SiS: 415.2001; found: 415.1994.
126.8, 126.7, 120.3, 55.4, 50.3, 38.4, 28.0, 22.7, 21.5, 20.9,
0.8. HRMS: m/z calcd for C26H33NO2SiS: 451.2001; found:
451.2008.
Compound 4b: 1H NMR (200.13 MHz, CDCl3): d = 0.13 (s,
9 H, SiMe3), 1.24 (s, 3 H, Me), 1.54 (s, 3 H, Me), 1.95 (m, 1
H, CH), 2.44 (s, 3 H, Me), 3.44 (dd, J = 4.1, 9.5 Hz, 1 H,
NCH2), 3.46 (d, J = 9.5 Hz, 1 H, NCH2), 3.60 (d, J = 9.1 Hz,
1 H, NCH2), 3.79 (s, 3 H, OMe), 4.04 (d, J = 9.1 Hz, 1 H,
NCH2), 5.61 (s, 1 H, =CHSiMe3), 6.70 (m, 3 H, p-
C6H4OMe), 7.29 (m, 3 H, p-C6H4OMe + Ph), 7.67 (d, J = 8.2
Hz, 2 H, Ph). 13C NMR (75.47 MHz, CDCl3): d = 158.2,
154.2, 147.2, 142.7, 142.4, 131.5, 128.7, 126.6, 118.5, 54.6,
54.4, 49.5, 37.4, 27.2, 20.7, 20.2, 19.5, 0.0. HRMS: m/z
calcd for C27H35NO3SiS: 481.2107; found: 481.2101.
Compound 6: 1H NMR (300.13 MHz, CDCl3): d = 0.20 (s, 9
H, SiMe3), 1.67 (s, 3 H, Me), 1.71 (s, 3 H, Me), 1.89 (m, 1
H, CH), 2.35 (dd, J = 4.6, 12.6 Hz, 1 H, NCH2), 2.50 (d, J =
12.3 Hz, 1 H, NCH2), 2.81 (d, J = 12.6 Hz, 1 H, NCH2), 3.03
(d, J = 12.3 Hz, 1 H, NCH2), 3.64 (s, 3 H, OMe), 3.70 (s, 3
H, OMe), 5.44 (d, J = 15.5 Hz, 1 H, =CHSiMe3), 6.11 (d, J =
15.5 Hz, 1 H, CH=). 13C NMR (75.47 MHz, CDCl3): d =
172.0, 171.2, 148.4, 128.1, 127.1, 125.0, 59.4, 52.9, 52.6,
39.7, 36.1, 35.9, 29.8, 22.2, 21.5, 1.20. HRMS: m/z calcd for
C18H28O4Si: 336.1757; found: 336.1750.
Compound 4a: 1H NMR (200.13 MHz, CDCl3): d = 0.13 (s,
9 H, SiMe3), 1.20 (s, 3 H, Me), 1.53 (s, 3 H, Me), 1.94 (m, 1
H, CH), 2.44 (s, 3 H, Me), 3.46 (dd, J = 4.1, 9.7 Hz, 1 H,
NCH2), 3.48 (d, J = 9.2 Hz, 1 H, NCH2), 3.60 (d, J = 9.6 Hz,
1 H, NCH2), 4.06 (d, J = 9.2 Hz, 1 H, NCH2), 5.60 (s, 1 H,
=CHSiMe3), 7.07 (m, 2 H, Ph), 7.31 (m, 5 H, Ph + Ts), 7.78
(d, J = 8.2 Hz, 2 H, Ts). 13C NMR (75.47 MHz, CDCl3): d =
155.2, 146.6, 143.2, 134.3, 132.5, 129.5, 127.8, 127.4,
(27) (a) Wegner, H. A.; De Meijere, A.; Wender, P. A. J. Am.
Chem. Soc. 2005, 127, 6530. (b) Wender, P. A.; Haustedt,
L. O.; Lim, J.; Love, J. A.; Williams, T. J.; Yoon, J.-Y. J. Am.
Chem. Soc. 2006, 128, 6302.
Synlett 2008, No. 2, 193–196 © Thieme Stuttgart · New York

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