New monoorganostannanes as efficient reagents for palladium-catalyzed coupling reactions

Full text of DOI:10.1021/jo970465g

5242
J . Org. Chem. 1997, 62, 5242-5243
Communications
New Mon oor ga n osta n n a n es a s Efficien t
Rea gen ts for P a lla d iu m -Ca ta lyzed
Cou p lin g Rea ction s
Eric Fouquet,* Michel Pereyre, and
Alain L. Rodriguez
F igu r e 1.
Laboratoire de Chimie Organique et Organome´tallique,
URA CNRS No. 35, Universite´ Bordeaux I,
351 Cours de la Libe´ration, 33405 Talence Cedex, France
F igu r e 2.
Received March 14, 1997
Ta ble 1. Rea ction of Allyltin s w ith Ben zylic Br om id es
The creation of carbon-carbon bonds using organotin
reagents and a transition-metal catalyst has been widely
developed in the last 10 years. While several metals have
shown their ability to promote this type of reaction, the
most popular method remains by far the palladium-
catalyzed reaction, also named Stille coupling.1 It has
always been asserted for this reaction that the reactivity
of the organotin reagent was critically dependent on the
substitution of the tin atom.2 Until recently, the deac-
tivating nature of halogen ligands discouraged the use
of monoorganotins for metal-catalyzed coupling reactions.
Although trihalogenoorganotins have been used for Stille
couplings in aqueous solution,3 the strongly basic condi-
tions required are a serious limitation for synthetic
purposes. With the aim of promoting the chemistry of
nontoxic and easily removable tin reagents, we were
interested in the direct synthesis of new monoallyltins
2a -c prepared from Lappert’s stannylene 1,4 which was
shown to be efficient for radical allylic transfer.5 The
possibility of conceiving one-pot procedures in which
organotin reagents are formed in-situ encouraged us to
assess the ability of these monoallyltins for coupling
reactions with organic halides under palladium0 catalysis
(Figure 1).
product
yield (%)
allyltin
E
substrate
R
condns
(°C, h)
X
2a
2b
2c
2a
2a
4
CO2Et
CN
Cl
CO2Et
CO2Et
CO2Et
Br
Br
I
Br
Br
Bu3
CO2Me
CO2Me
CO2Me
H
Me
CO2Me
90
110
110
110
90
0.2
2
3
0.2
2
3a
71
54
44
65
66
56
3b
3c
3d
3e
3a
110
0.2
influence of pentacoordination on the limiting step of the
reaction is outlined with 2b and 2c, which do not undergo
such an intramolecular complexation. Then, compared
to 2a , their lower reactivity made the reaction ineffective
at 90 °C and forced it to be carried out at 110 °C with a
10-fold longer reaction time. The activating effect caused
by an additional coordination of the tin atom has been
established recently for tetraorganotins7 and the transfer
of the extra coordination from tin to palladium is also
accounted for, explaining the rate acceleration.8 Never-
theless, this is the first time that this has been shown
for the transfer of allyl groups from monoorganotins,
which are believed to be far less reactive in Stille coupling
than organotins with tin-sp2 carbon bonds.
The results shown in Table 1 reveal the ability of
monoallyltins 2 to achieve the coupling reaction with
benzylic substrates. An impressive result in term of
reactivity is obtained when using the intramolecularly
coordinated organotin 2a , which appears to be even more
efficient than the parent tetraalkyl organotin 4.6 The
The ready avaibility of these monoorganotins, in
quantitative yields, simply starting from the correspond-
ing organic halides led us to turn our attention to various
types of monoorganotin reagents. In order to take
advantage of the nucleophilic assistance brought by the
coordination, we modified our initial system by adding 3
equiv of TBAF (tetrabutylammonium fluoride), so that
the active organotin can be considered as the pentavalent
difluorinated tin A (Figure 2).9 The ease of halogen
replacement by a fluorine atom has been widely used for
the removal of organotins side products.10 Moreover,
hypervalent fluorinated organotin species have been
known for over a decade,11 but, in contrast with their
organosilicon counterparts12, their use for synthetic
* To whom correspondence should be addressed: Tel: +33 05 56 84
28 29. Fax: +33 05 56 84 69 94. E-mail: e.fouquet@lcoo.u-bordeaux.
fr.
(1) Mitchell, T. N. Synthesis 1992, 803. Farina, V. In Comprehensive
Organometallic Chemistry, 2nd ed.; Abel, E. A., Stone, F. G. A.,
Wilkinson, G., Eds.; Pergamon Press: London, 1995; Vol. 12, pp 200-
221. Farina, V. Pure Appl. Chem. 1996, 68, 73. Hegedus, L. S. Coord.
Chem. Rev. 1996, 147, 443.
(2) (a) Stille, J . K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508. (b)
Yamamoto, Y.; Hatsuya, S.; Yamada, J . J . Org. Chem. 1990, 55, 3118.
(3) Roshchin, A. I.; Bumagin, N. A.; Beletskaya, I. P. Tetrahedron
Lett. 1995, 36, 125. Rai, R.; Aubrecht, K. B.; Collum, D. B. Tetrahedron
Lett. 1995, 36, 3111.
(4) Harris, D. H.; Lappert, M. F. J . Chem. Soc., Chem. Commun.
1974, 895. Schaeffer, C. D.; Zuckerman, J . J . J . Am. Chem. Soc. 1974,
96, 7160. Lappert, M. F.; Misra, M. C.; Onyszchuk, M.; Rowe, R. S.;
Power, P. P.; Slade, M. J . J . Organomet. Chem. 1987, 330, 31.
(5) Fouquet, E.; Pereyre, M.; Roulet, T. J . Chem. Soc., Chem.
Commun. 1995, 2387.
(6) The intramolecular coordination of the tin atom by the carbonyl
group is clearly shown by IR spectroscopy with the bathochromic shift
of the carbonyl band (1663 cm-1 for 2a compared to 1710 cm-1 for 4).
This also influences the 119Sn NMR spectrum by shielding the signal
(δ ) -129.1 ppm for 2a compared to -81.8 ppm for 2b and -84.6 ppm
for 7). For similar phenomena observed on monoallyltrihalogenotins
see also: Fouquet, E.; Gabriel, A.; Maillard, B.; Pereyre, M. Bull. Soc.
Chim. Fr. 1995, 132, 590.
(7) Brown, J . M.; Pearson, M.; J astrzebski, J . T. B. H.; Van Koten,
G. J . Chem. Soc., Chem. Commun. 1992, 1440. Vedejs, E.; Haight, A.
R.; Moss, W. O. J . Am. Chem. Soc. 1992, 114, 6556.
(8) Crisp, G. T.; Gebauer, M. G. Tetrahedron Lett. 1995, 36, 3111.
(9) Three equivalents are the optimal amount of TBAF to form the
active organotin A all along the reaction. The first equivalent readily
gives the insoluble monofluoroorganotinIV, the second one changes it
to the soluble difluoroorganotinV anion A, and the third equivalent is
consumed for the halogen exchange of the tin-halogen bond created
during the coupling.
(10) Leibner, J . E.; J acobus, J . J . Org. Chem. 1979, 44, 449. Barton,
D. H. R.; Motherwell, W. B.; Stange, A. Synthesis 1981, 743.
(11) Crawe, A. J . J . Organomet. Chem. 1982, 224, 223. Blunden,
S. J .; Hill, H. J . Organomet. Chem. 1989, 371, 145. Gingras, M.
Tetrahedron Lett. 1991, 32, 7381.
(12) Hiyama, T. ; Hatanaka, Pure Appl. Chem. 1994, 66, 1471.
S0022-3263(97)00465-9 CCC: $14.00 © 1997 American Chemical Society

Communications
J . Org. Chem., Vol. 62, No. 16, 1997 5243
Ta ble 2. P a lla d iu m 0-Ca ta lyzed Rea ction of Mon oor ga n otin s w ith Ar yl a n d Vin yl Iod id es
products 17 and 18. The allenyl transfer is also achieved
under particularly mild conditions (Table 2, entry 6),20
and double bond stereochemistry is totally preserved
(Table 2, entries 9 and 10). Then, the use of a vinyl iodide
as substrate allows a straightforward preparation of
diene unit 23.
Finally, it is noteworthy that all the products are
obtained free of organotin contamination, since the
trifluorotin side product is easily removed. Thus is solved
a major drawback of the use of organotins reagents in
Pd-catalyzed coupling reactions. In conclusion, the direct
and quantitative preparation of monoorganotin reagents
from Lappert’s stannylene avoids syntheses and purifica-
tions of intermediate tetraorganotins. Moreover, their
high reactivity to undergo cross-coupling reactions as well
as the ease in the removal of tin side products clearly
highlight their synthetic value, which is currently under
investigation.
purposes has been rather limited until now.13 An excep-
tion can be noted from a recent communication,14 in
which TBAF was also used for activating tetraorganotins.
The results are summarized in Table 2 and show the
wide range of utility of these monoorganotins, which are
active with less than 1% of Pd(PPh3)4.15 It can be pointed
out that, contrary to the common organotin compounds
used in Stille coupling, these reagents are able to transfer
alkyl groups in good yields (Table 2, entries 1 and 2).6,16
There are also major changes in the reactivity order,17
which can be considered as the following: allyl ≈ crotyl
≈ allenyl > alkynyl > alkenyl ≈ aromatic ≈ alkyl.
Furthermore, this reaction appears to be totally regiose-
lective for crotyl (Table 2, entry 4)18 or prenyl transfer
(Table 2, entry 5),19 affording exclusively the transposed
(13) Martinez, A. G.; Barcina, J . O.; de Fresno Cerezo, A.; Subra-
manian, L. R. Synlett 1994, 1047.
(14) Buffnoir, S.; Mestdagh, E.; Rolando, C. Electron. Conf. Trends
Org. Chem. [CD-ROM], Rzepa, H. S.; Leach, C.; Goodman, J . M., Eds.;
Royal Chemical Society: Cambridge, 1996, Paper 42.
(15) Typical procedure: 1-Iodohexyne (1.85 mmol) was added to a
solution of stannylene 1 (1.85 mmol) in THF (4 mL) and stirred for 30
min at rt. TBAF (5.9 mL, 1 M) was added, after concentration, dioxane
(8 mL), iodobenzene (1.23 mmol), and tetrakis(triphenylphosphine)-
palladium (0.015 mmol) were added, and the reaction mixture was
refluxed for 2 h. After cooling and removal of the solvent, purification
on silica gel afforded 20 in 83% yield.
(16) Brigas, A. F.; J ohnstone, A. W. J . Chem. Soc., Chem. Commun.
1992, 1440. Mamos, P.; Van Aershot, A. A.; Weyns, N. J .; Herdewijn,
P. A. Tetrahedron Lett. 1992, 33, 2413.
Su p p or tin g In for m a tion Ava ila ble: Preparation proce-
dure and NMR data (1H, 13C, 119Sn) of monoorganotins 2a -c
and 5-13, experimental procedures for both types of coupling
reactions, and characterization of coupling products 3a -e and
14-23 (5 pages).
J O970465G
(18) Echavarren, A. M.; Stille, J . K. J . Am. Chem. Soc. 1987, 109,
5478. Obora, Y.; Tsuji, Y.; Kobayashi, M.; Kawamura, T. J . Org. Chem.
1995, 60, 4647.
(19) Trost, B. M.; Keinan, E. Tetrahedron Lett. 1980, 21, 2595.
(20) Badone, D.; Cardamone, R.; Guzzi, U. Tetrahedron Lett. 1994,
30, 5477.
(17) Stille, J . K. Pure Appl. Chem. 1985, 57, 1771.