Allylsilane-vinylcopper reagents: Palladium-mediated coupling with alkenyl halides. Synthesis and photochemical [2+2] cyclization of (±)-Ipsdienol

Article abstract of DOI:10.1055/s-2001-14589

Reaction of phenyldimethylsilyl-copper with 1,2-propadiene followed by Pd⁰ catalyzed coupling of the resulting copper intermediate with alkenyl halides affords allylsilane-containing dienes in high yield. Coupling with vinyl bromide gives 2-phenyldimethylsilylmethylbuta-1,3-diene which is an isoprenyl building block for the synthesis of (±)-Ipsenol and (±)-Ipsdienol, the aggregation pheromones of the Ips bark beetle. The photochemical [2+2] cyclization of Ipsdienol was also studied.

Full text of DOI:10.1055/s-2001-14589

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24
LETTER
Allylsilane-Vinylcopper Reagents: Palladium-Mediated Coupling with
Alkenyl Halides. Synthesis and Photochemical [2+2] Cyclization of
(
)-Ipsdienol
Asunción Barbero, Carlos García, Francisco J. Pulido*
Departamento de Química Orgánica, Universidad de Valladolid, 47011 Valladolid, Spain
Fax +34 (983) 423013; E-mail: pulido@qo.uva.es
Received 22 March 2001
they were transmetallated with zinc halides or activated
with magnesium salts respectively.
Abstract: Reaction of phenyldimethylsilyl-copper with 1,2-propa-
diene followed by Pd catalyzed coupling of the resulting copper in-
0
termediate with alkenyl halides affords allylsilane-containing In this paper we report the palladium mediated coupling
dienes in high yield. Coupling with vinyl bromide gives 2-phe-
nyldimethylsilylmethylbuta-1,3-diene which is an isoprenyl build-
ing block for the synthesis of ( )-Ipsenol and ( )-Ipsdienol, the
aggregation pheromones of the Ips bark beetle. The photochemical
reactions of the allylsilane-vinylcopper reagent 1 with
alkenyl halides and we demonstrate an alternative isopre-
8
nylation method, using our silylcuprate chemistry, which
can be readily applied to the construction of terpenoid
[
2+2] cyclization of Ipsdienol was also studied.
structures. Application of this chemistry resulted in a
Key words: allylsilane, vinylcopper, palladium, cross-coupling,
photocyclization
9
9
short synthesis of ( )-Ipsenol and ( )-Ipsdienol, the
principal components of the aggregation pheromones of
the Ips bark beetle.10 Moreover, the study of the photo-
chemical [2+2] cyclization of Ipsdienol, as an expedient
route for the preparation of bicyclic monoterpenoid units,
is described.
Recent findings from our laboratory1-3 have shown that
phenyldimethylsilylcopper(I), prepared from one equiva-
4
lent of phenyldimethylsilyllithium and copper(I) cya-
1
,2-Propadiene gas (excess) was bubbled through a solu-
nide, reacts with 1,2-propadiene (allene) in THF, at
temperatures below 40 °C, leading to a regiochemically
stable allylsilane-vinylcopper species 1 (associated with
LiCN) which affords high yields of functionalized allylsi-
lanes after quenching the reaction with an electrophile.
The reaction is known to proceed by syn-addition of the
Si-Cu bond to allene through a rapid and reversible mech-
anism for which we have reported significant evidence.5
Control of the regioselectivity is extremely high, provided
the temperature of the process does not exceed -40 °C.
This route is an easy and convenient entry to differently
substituted allylsilanes whose usefulness as powerful sili-
1
tion of phenyldimethylsilylcopper (4 mmol, 78 °C to
0 °C, 30 min) in THF (6 mL). The resulting organocop-
4
per reagent 1 was added (via canula) to a mixture of the
vinylic halide11 (6 mmol) and Pd(Ph P) (0.2 mmol) in
3
4
THF (10 mL), at 40 °C. After stirring for 2 h at 40 °C,
the mixture was warmed up to 0 °C and quenched with
saturated aqueous NH Cl affording high yields of the al-
4
12
lylsilane-containing dienes 2-5 (Scheme 1). Under the
same conditions, iodobenzene leads to the silylated sty-
rene 6.
3
con-synthons we recently demonstrated. Thus, the use of
R
-
unsaturated ketones as electrophiles, and the subse-
X
R
quent intramolecular cyclization of the oxyallylsilanes
produced, allowed the design of new protocols for cyclo-
pentane annulations and easy access to exocyclic methyl-
enecyclopentanols, the latter moiety being abundant in
Pd(Ph3P)4
+
PhMe2Si
1
Cu
THF, –40 °C, 2 h
PhMe2Si
Ph
2: R=H, X=Br (85%)
3
: R=Ph, X=Br (75%)
3
PhMe2Si
some families of cyclopentanomonoterpenes. The same
4: R=C H , X=I (89%)
4
9
6
(88%)
5: R=(CH2)7CH3, X=I (81%)
annulation procedure has been successfully used for the
synthesis of fused cis-anti-cis-tricyclopentanoids, thus
providing an easy approach to linearly fused triquinane
Scheme 1
3
natural products.
On the other hand, although palladium catalyzed coupling
of organometallics with vinyl halides has been largely
The reactions were carried out in the absence of other met-
al salts, and from our preliminary work it seems that the
presence of magnesium or zinc salts is not necessary, in-
dicating that transmetallation or activation was not re-
quired. The regioselectivity of the reaction seems to be
complete, we were not able to detect other regioisomers
by NMR and GC-MS. In fact, protonation of 1 at 40 °C
provides almost quantitative yields of phenyldimethyl-
6
studied, the use of alkenylcopper reagents has received
7
little attention. In fact, Normant et al. reported that, under
palladium(0) catalysis, lithium alkenylcuprates as well as
alkenylcopper reagents (associated with lithium salts)
showed very little reactivity toward vinyl halides, unless
Synlett 2001, No. 6, 824–826 ISSN 0936-5214 © Thieme Stuttgart · New York

LETTER
Allylsilane-Vinylcopper Reagents
825
allylsilane. Allylsilanes are known to be good
1
3
14
nucleophiles and therefore diene 2 can be formally
considered as a synthetic equivalent to an isoprenyl anion
moiety which might be conveniently coupled to an elec-
trophilic carbon center. Thus, following Sakurais meth-
odology but using 2 instead of the trimethylsilyl analogue,
1
5
OH
OH
1
0 (85%)
hν/(C6H5)2CO
and EtAlCl as the Lewis acid, we were able to prepare
8
2
hexane, r.t., 5–8 h
(
)-Ipsenol 7 and ( )-Ipsdienol 8 with markedly improved
yields (Scheme 2).
OH
< (5%, NMR)
OH
9
CHO / Et2AlCl2
H
PhMe2Si
Toluene, 0 ºC, 1 h
OH
H
H
2
Me
O
7 (87%)
(±)-ipsenol
1.
Me
H
Cl / AlCl3
CH2Cl2, –60 ºC, 15 min
HO
OH
(±)-ipsdienol
2
. DIBAH
Scheme 3
Toluene, –40 to 0 ºC, 4 h
8 (85%)
Scheme 2
steps respectively, in 87% and 85% overall yield. Photo-
It seems clear that the phenyldimethylsilyl group is a cyclization of ( )-Ipsdienol gives bicyclo[2.1.1]hexanol
much more efficient group for coupling reactions between 10 rather than bicyclo[3.1.1]heptanol 9.
allylsilanes and aldehydes than the trimethylsilyl group.
The use of other Lewis acids (BF , TiCl ) or TBAF lowers
the yield significantly. Preparation of 8 is better acom-
3
4
Acknowledgement
plished from the acid chloride than from 3-methylcro- We gratefully acknowledge financial support from the Ministry of
Education and Science of Spain (DGES project PB96/0357) and
from the "Junta de Castilla y León" (project VA43/98).
tonaldehyde due to the known tendency of unsaturated
aldehides to polymerize. Physical and spectroscopic data
for 7 and 8 were identical to those previously reported for
1
6
(
)-Ipsenol and ( )-Ipsdienol.
References and Notes
We also considered whether intramolecular [2+2] photo-
cyclization of the polyene moiety of 8 could be envisaged
as a feasible pathway for the construction of bicyc-
lo[3.1.1]heptanes of the verbenol family. However, upon
irradiation of 8 (hexane, r.t., 5 h) with a tungsten lamp
(
1) Blanco, F.J.; Cuadrado, P.; González, A.M.; Pulido, F.J.;
Fleming, I. Tetrahedron Lett. 1994, 35, 8881.
(2) Barbero, A.; García, C.; Pulido, F.J. Tetrahedron Lett. 1999,
0, 6649.
4
(
(
(
3) Barbero, A.; García, C.; Pulido, F.J. Tetrahedron Symposium-
in-Print "Organocopper Chemistry II" 2000, 56, 2739.
4) Cuadrado, P.; González, A.M.; Pulido, F.J.; Fleming, I.;
Rowley, M. Tetrahedron 1989, 45, 413.
5) Fleming, I.; Pulido, F.J. J. Chem. Soc., Chem. Commun. 1986,
1010. Cuadrado, P.; González, A.M.; Pulido, F.J.; Fleming, I.
Tetrahedron Lett. 1988, 29, 1825. Barbero, A.; Cuadrado, P.;
González, A.M.; Pulido, F.J.; Fleming, I. J. Chem. Soc.,
Perkin Trans. 1 1991, 2811. Blanco, F.J.; Cuadrado, P.;
González, A.M.; Pulido, F.J. Synthesis 1996, 42. Fleming, I.;
Landais, Y.; Raithby, P.R. J. Chem. Soc., Perkin Trans. 1
(
400 W) using a small amount of benzophenone (10%
mol.) as photosensitizer gave the verbenol derivative 9 in
only 5% yield (NMR) and the pseudoterpenoid alcohol 10
in 85% yield (Scheme 3). In the absence of the photosen-
sitizer the reaction proceeds very slowly. The stereochem-
istry of 10 has been asigned from NOESY experiments
and indicates a preference for the transition state depicted
in Scheme 3, where the OH group is arranged anti to the
gem-dimethyl group for minimal repulsions.
1991, 715. See also ref 4 and citations therein.
(
(
6) Transition Metals for Organic Synthesis; Beller, M. and
Bolm, C. Eds.; Wiley-VCH: Weinheim, 1998, Vol 1. Metal-
catalyzed Cross-coupling Reactions; Diederich, F. and Stang,
P.J. Eds.; Wiley-VCH: Weinheim, 1998.
In summary, silylcupration of allene followed by palladi-
um mediated coupling with alkenyl halides gives allylsi-
lane-containing dienes in high yields, thus showing that
unactivated vinylcopper intermediates can be successfully
used in palladium catalyzed cross-coupling reactions.
Formally, the overall process can be seen as a Stille-like
coupling without mediation of toxic tin reagents. The al-
lylsilane moiety can further be used in subsequent reac-
tions. Thus, compound 2 is an isoprenyl building block
and a key intermediate in the synthesis of ( )-Ipsenol and
7) Jabri, N.; Alexakis, A.; Normant, J.P. Bull. Soc. Chim. Fr.
1983, 321 and 332. Gardette, M.; Jabri, N.; Alexakis, A.;
Normant, J.P. Tetrahedron 1984, 2741.
(8) For a review about our previous work on silylcupration of
allenes and acetylenes see ref 1-5 and Barbero, A.; Cuadrado,
P.; Fleming, I.; González, A.M.; Pulido, F.J.; Sánchez, A. J.
Chem. Soc., Perkin Trans. 1 1995, 1525. See also Fleming, I.;
Newton, T.W.; Roessler, F. J. Chem. Soc., Perkin Trans. 1
(
)-Ipsdienol which were prepared from 2 in one or two
1981, 2527.
Synlett 2001, No. 6, 824–826 ISSN 0936-5214 © Thieme Stuttgart · New York

8
26
A. Barbero et al.
LETTER
(9) For recent syntheses of ipsenol and ipsdienol see: Hosomi, A.;
131.2 (HC=), 128.8 (CH, Ph), 127.6 (CH, Ph), 112.2 (H C=),
2
Araki, Y.; Sakurai, H. J. Org. Chem. 1983, 48, 3122 and
Tetrahedron Lett. 1979, 429. Nishigaichi, Y.; Kuramoto, H.;
Takuwa, A. Tetrahedron Lett. 1995, 36, 3353. Chevtchouk,
T.A.; Isakov, V.E.; Kulinkovich, O.G. Tetrahedron 1999, 55,
32.4 (CH ), 31.5 (CH ), 22.3 (CH ), 21.3 (CH -Si), 13.9
2
2
2
2
(CH ), –2.8 (Me -Si).
3
2
(13) Weber, W.P. Silicon Reagents for Organic Synthesis;
Springer-Verlag: Heidelberg, 1983. Schinzer, D. Synthesis
1988, 263. Majetich, G.; Lowery, D.; Khetani, V.; Song, J.S.;
Hull, K.; Ringold, C. J. Org. Chem. 1991, 56, 3988. White,
J.B.; Fan, W. Tetrahedron Lett. 1997, 38, 7155. See also:
Chan, T.H.; Fleming, I. Synthesis 1979, 761. Fleming, I.;
Dunogues, J.; Smithers, R.H. Org. React. 1989, 37, 57.
(14) Organ, M.; Winkle, D. J. Org. Chem. 1997, 62, 1881.
(15) Hosomi, A.; Saito, M.; Sakurai, H. Tetrahedron Lett. 1979,
429. Hosomi, A.; Araki, Y.; Sakurai, H. J. Org. Chem. 1997,
62, 1881.
13205.
(
10) Byers, J.A. Host Tree Chemistry Affecting Colonization in
Bark Beetles. In Chemical Ecology of Insects 2.; Carde, R.T.
and Bell, W.J. Eds.; Chapman and Hall: New York, 1995, p
154. Silverstein, R.M.; Rodin, J.O.; Wood, D.L. J. Econ.
Entomol. 1967, 60, 944 and Science 1966, 154, 509.
11) The starting vinyl halides were commercially available or
prepared from the corresponding acetylene by
(
(
hydroalumination (DIBAH) and quenching with iodine.
1
12) 3: H NMR (300 MHz, CDCl ) 7.58-7.38 (m, 5H, Ph), 6.07
(16) Karlsen, S.; Froyen, P.; Skattebol, L. Acta Chem. Scand. B
1976, 30, 664.
3
(d, J = 15.7 Hz, 1H, HC=), 5.53 (dt, J = 15.7 and 7.1 Hz, 1H,
HC=), 4.83 (d, 1H, J = 1.5 Hz, HHC=), 4.67 (d, 1H, J = 1.5
Hz, HHC=), 2.13 (dt, 2H, J = 7.1 and 6.7, CH -C=), 1.97 (s,
2
2
H, CH -Si), 1.40-1.31 (m, 4H, 2CH ), 0.93 (t, 3H, J = 7.0,
Article Identifier:
1437-2096,E;2001,0,06,0824,0826,ftx,en;D05201ST.pdf
2
2
1
3
CH ), 0.32 (s, 6H, Me Si); C NMR (75 MHz, CDCl3)
3
2
143.3 (=C), 139.3 (C, Ph), 133.6 (CH, Ph), 132.7 (HC=),
Synlett 2001, No. 6, 824–826 ISSN 0936-5214 © Thieme Stuttgart · New York