Organoheteroatom stannanes in palladium-catalyzed cross-coupling reactions with 1-naphthyl triflate

Article abstract of DOI:10.1021/om8009816

We have studied the Pd-catalyzed cross-coupling reaction of organoheteroatom stannanes containing elements of groups 15 (P, As, Sb) and 16 (Se) with 1-naphthyl triflate (3). The stannanes n-Bu₃SnZPh _n (Z = P, As, Sb, Se; n = 1,2) wer

Full text of DOI:10.1021/om8009816

Organometallics 2009, 28, 933–936
933
Organoheteroatom Stannanes in Palladium-Catalyzed
Cross-Coupling Reactions with 1-Naphthyl Triflate
Mariana Bonaterra, Roberto A. Rossi,* and Sandra E. Mart´ın*
INFIQC, Departamento de Qu´ımica Orga´nica, Facultad de Ciencias Qu´ımicas, UniVersidad Nacional de
Co´rdoba, Haya de Torre y Medina Allende, 5000 Co´rdoba, Argentina
ReceiVed October 10, 2008
S, Se, Te) have been used as nucleophiles in synthesis, only a
few examples of their application in cross-coupling reactions
with organic triflates have been reported. The Pd-catalyzed
coupling of enol triflates with (Me3Sn)2 afforded the vinylstan-
nanes regiochemically.7 Furthermore, Pd-mediated C-S8 and
C-Se9 bond forming reactions have been achieved. Other
reported methods include the Pd-catalyzed coupling of aryl
triflates with Ph2P(O)H10 and Ph2PH.11 Shibasaki and co-
workers have described the nickel-catalyzed arsination of
BINOL ditriflate using Ph2AsH for the synthesis of the BINAs
ligand.12 Aryl sulfides have also been obtained by the Pd-
catalyzed reaction of PhSH with ArOTf.13
Summary: We haVe studied the Pd-catalyzed cross-coupling
reaction of organoheteroatom stannanes containing elements
of groups 15 (P, As, Sb) and 16 (Se) with 1-naphthyl triflate
(3). The stannanes n-Bu3SnZPhn (Z ) P, As, Sb, Se; n ) 1, 2)
were synthesized by the reaction of the PhnZ- anion with
n-Bu3SnCl. The cross-coupling reactions of these stannanes with
3 in a one-pot procedure afforded the C-heteroatom products
PhnZ-1-Naph in good yields for Z ) As, Se (90 and 70% yields,
respectiVely) and moderate yields for Z ) P (51% yield). Only
18% of 1-naphthyldiphenylstibine was obtained. Optimization
studies reVealed that the combination of LiCl and free PPh3
ligand proVed to be particularly effectiVe in enhancing the
coupling reaction.
We have developed a versatile methodology that allows for
C-heteroatom bond formation through a cross-coupling Pd-
catalyzed reaction of different electrophiles with the organo-
heteroatom stannanes R3SnZPhn (Z ) P, As, Sb, Se) in a one-
pot, two-step reaction.2e,g,i The in situ generation of the
stannanes R3SnZPhn eliminates the isolation and purification of
tin reagents. To extend the applications of this methodology,
we studied the Pd-catalyzed cross-coupling of organoheteroatom
stannanes containing group 15 (P, As, Sb) and 16 elements (Se)
with 1-naphthyl triflate (Scheme 1). Herein, we report on the
scope and limitations of the organoheteroatom stannanes
R3SnZPhn (Z ) P, As, Sb, Se) in coupling reactions.
The palladium-catalyzed cross-coupling reaction of organic
electrophiles with organostannanes is a widely used methodol-
ogy for C-C1 and C-heteroatom2 bond formation under
conditions compatible with a broad range of functional groups,
the aryl halides being one of the most thoroughly studied
groups.1 However, as organic triflates are readily available, they
have become important coupling partners in synthesis. Stille
and co-workers have studied the scope and limitation of the
cross-coupling reactions of triflates with organostannanes.3 A
number of effective palladium-catalyzed coupling reactions have
been developed for vinyl and aryl triflates as electrophiles.4 An
extensive study of the mechanism of the coupling of triflates
with vinyltributyltin was carried out.5 Also, the rate and
mechanism of the oxidative addition of vinyl triflates was
studied.6
In previous work, we found that the one-pot cross-coupling
reaction of 1-naphthyl triflate (3) with n-Bu3SnAsPh2 (1a)
affords naphthalen-1-yldiphenylarsine (4) in 68% yield.2g Cur-
rently, we decided to study extensively the coupling reaction
It should be noted that, although organotin compounds with
group 14 (Si, Sn, Ge), 15 (N, P, As, Sb), and 16 elements (O,
(4) (a) Fu, J. M.; Snieckus, V. Tetrahedron Lett. 1990, 31, 1665–1668.
(b) Ohe, T.; Miyuara, N.; Suzuki, A. Synlett 1990, 221–222. (c) Saa´, J. M.;
Martorell, G.; Garcia-Raso, A. J. Org. Chem. 1992, 57, 678–685. (d) Farina,
V.; Krishnan, B.; Marshall, D. R.; Roth, G. P. J. Org. Chem. 1993, 58,
5434–5444. (e) Saa´, J. M.; Martorell, G. J. Org. Chem. 1993, 58, 1963–
1966. (f) Dom´ınguez, B.; Pazos, Y.; de Lera, A. R. J. Org. Chem. 2000,
65, 5917–5925.
(5) Casado, A. L.; Espinet, P.; Gallego, A. J. Am. Chem. Soc. 2000,
122, 11771–11782.
(6) Jutand, A.; Ne´gri, S. Organometallics. 2003, 22, 4229–4237.
(7) Winstead, R. C.; Simpson, T. H.; Lock, G. A.; Schiavelli, M. D.;
Thompson, D. W. J. Org. Chem. 1986, 51, 277–279.
(8) Rossi, R.; Bellina, F.; Mannina, L. Tetrahedron 1997, 53, 1025–
1044.
(9) Beletskaya, I. P.; Sigeev, A. S.; Peregudov, A. S.; Petrovskii, P. V.
J. Organomet. Chem. 2000, 605, 96–101.
(10) For some examples, see: (a) Gelpke, A. E. S.; Kooijman, H.; Spek,
A. L.; Hiemstra, H. Chem. Eur. J. 1999, 5, 2472–2482. (b) Vyskoe`yl, S.;
Smre`ina, M.; Hanusˇ, V.; Pola´sˇek, M.; Koe`ovsky´, P. J. Org. Chem. 1998,
63, 7738–7748. (c) Martorell, G.; Garc´ıas, X.; Janura, M.; Saa´, J. M. J.
Org. Chem. 1998, 63, 3463–3467. (d) Kurz, L.; Lee, G.; Morgans, D.;
Waldyke, M. J.; Ward, T. Tetrahedron Lett. 1990, 31, 6321–6424.
(11) Cai, D.; Payack, J. F.; Bender, D. R.; Hughes, D. L.; Verhoeven,
T. R.; Reider, P. J. J. Org. Chem. 1994, 59, 7180–7181.
(12) Kojima, A.; Boden, C. D. J.; Shibasaki, M. Tetrahedron Lett. 1997,
38, 3459–3460.
* To whom correspondence should be addressed. Tel: 54-351-4334170.
Fax: 54-351-4333030. E-mail: martins@fcq.unc.edu.ar.
(1) Farina, V.; Krishnamurthy, V.; Scott, W. J. The Stille Reaction;
Paquette, L. A., Ed.; Wiley: New York, 1997; Organic Reactions, Vol. 50.
(2) For some examples of C-N bond formation see: (a) Kim, Y. O.;
Yu, S. J. Am. Chem. Soc. 2003, 125, 1696–1697. (b) Koza, D. J.; Nsiah,
Y. A. J. Org. Chem. 2002, 67, 5025–5027. (c) Paul, F.; Hartwing, J. F.
J. Am. Chem. Soc. 1994, 116, 5969–5970. (d) Guran, A. S.; Buchwald,
S. L. J. Am. Chem. Soc. 1994, 116, 7901–7902. For C-P see: (e) Mart´ın,
S. E.; Bonaterra, M.; Rossi, R. A. J. Organomet. Chem. 2002, 664, 223–
227. (f) Tunney, S. E.; Stille, J. K. J. Org. Chem. 1987, 52, 748–753. For
C-As and C-Sb see: (g) Bonaterra, M.; Mart´ın, S. E.; Rossi, R. A. Org.
Lett. 2003, 15, 2731–2734. For C-S, C-Si, and C-Sn see: (h) Rossi, R. A.;
Mart´ın, S. E. Coord. Chem. ReV. 2006, 250, 575–601. For C-Se see: (i)
Bonaterra, M.; Mart´ın, S. E.; Rossi, R. A. Tetrahedron Lett. 2006, 47, 3511–
3515. (j) Wallner, O. A.; Szabo´, K. M. J. Org. Chem. 2005, 70, 9215–
9221. (k) Nishiyama, Y.; Sonoda, N. Mini-ReV. Org. Chem. 2005, 2, 147–
155. (l) Beletskaya, I. P.; Sigeev, A. S.; Peregudov, A. S.; Petrovskii, P. V.
Tetrahedron Lett. 2003, 44, 7039–7041. (m) Beletskaya, I. P.; Sigeev, A. S.;
Peregudov, A. S.; Petrovskii, P. V. J. Organomet. Chem. 2000, 605, 96–
101. (n) Nishiyama, Y.; Tokunaga, K.; Sonoda, N. Org. Lett. 1999, 1, 1725–
1727.
(3) (a) Scott, W. J.; Crisp, G. T.; Stille, J. K. J. Am. Chem. Soc. 1984,
106, 4630–4632. (b) Scott, W. J.; Stille, J. K. J. Am. Chem. Soc. 1986,
108, 3033–3040. (c) Stille, J. K.; Echavarren, A. M.; Williams, R. M.;
Hendrix, J. A. Org. Synth. 1993, 71, 97–106, and references cited therein.
(13) Mispelaere-Cavinet, C.; Spindler, J.-F.; Perrio, S.; Beslin, P.
Tetrahedron 2005, 61, 5253–5259.
10.1021/om8009816 CCC: $40.75
2009 American Chemical Society
Publication on Web 01/12/2009

934 Organometallics, Vol. 28, No. 3, 2009
Notes
Scheme 1
Couplings of triflates show several experimental features that
should be considered. One of them is the effect of the addition
of LiCl to the catalytic mixture, whose role may be positive,
negative, or neutral, depending on ligands and solvents. Stille
et al. found that this addition was necessary to achieve couplings
of organic triflates with organostannanes.3 However, this finding
cannot be generalized, since in many cases this salt can even
retard the coupling.16 Farina et al. studied this LiCl effect in
depth and found it to lead either to acceleration or retardation,
depending on the solvent and substrate used.17 Indeed, Cl-
modifies the kinetics of the oxidative addition of aryl triflates;5,18
it also modifies the second step of the catalytic cycle of the
Stille reaction5 by the formation of neutral complexes [Pd(Ar)(Cl)-
(PPh3)2], which then react with the organostannane.
In our system, the addition of LiCl did not produce any
noticeable effect in toluene (entry 2), probably because of its
low solubility.5 When we carried out the reaction in DMF, 25%
of 4 was obtained (entry 8). In this case, the reaction was slightly
retarded. However, the accelerating effect of LiCl during the
oxidative addition of Pd(PPh3)4 to 3 in DMF was observed.18,19
When additional PPh317,20 was added to the reaction mixture
in toluene, again no reaction was practically evidenced (entry
3). Likewise, when the reaction was carried out in DMF, the
yield of 4 was similar to that obtained without the ligand (entry
9 vs 7).
Table 1. Pd-Catalyzed Cross-Coupling Reactions with
n-Bu3SnAsPh2 (1a) and 1-Naphthyl Triflate (3)a
ligand Pd:L amt of additive cocat. CuI
entry solvent
(1:4)
LiCl (equiv)
(Pd:Cu)
4 (%)b
1
2
toluene
toluene
2
3
5
3
3
3
3
3
4
5
6
toluene PPh3
toluene PPh3
toluene AsPh3
toluene PPh3
DMF
3
3
3
1:2
1:2
7
35
25
28
68
59
90 (82)
10
15
8
DMF
3
9
DMF
DMF
DMF
DMF
DMF
DMF
PPh3
PPh3
PPh3 (1:40)
PPh3
AsPh3
AsPh3
10
11
12
13
14
3
3
3
3
a Reaction conditions: the Ph2As- anion was prepared in liquid
ammonia (300 mL) from AsPh3 (1 mmol) and Na metal (2 mmol); then
n-Bu3SnCl (1 mmol) was added. The cross-coupling reaction was
carried out with 3 (0.7 mmol) and (PPh3)2PdCl2 (1.5 mol %) for 24 h at
80 °C when toluene was used or at 120 °C with DMF. b CG yields and
isolated yields in parentheses.
The coupling reaction was delayed when AsPh3 was em-
ployed, and the yields of 4 were lower than those obtained with
PPh3 (entry 9 vs 13). The low rates found with AsPh3 as a ligand
may be due to the slowness of the oxidative addition of 3 to
Pd(0) species.5
with organoheteroatom stannanes. The experiments have been
performed with the objective of gaining insight into the general
effect of different additives, ligands, and solvent and of
establishing the optimal reaction conditions. We selected
1-naphthyl triflate (3) as a model triflate (eq 1); the results of
Pd-catalyzed cross-coupling with 1a are shown in Table 1.
A remarkable improvement in the yield of 4 (68%) was found
when the cross-coupling reaction was carried out with both LiCl
and PPh3 in DMF (entry 10). An increased amount of product
4 was also observed with AsPh3 as a ligand and LiCl (entry
14). Once again, practically no coupling reaction was observed
in toluene under these conditions (entries 4 and 5). The role of
LiCl appears to be strongly dependent not only on the solvent
but also on the addition of the free ligand. The combination of
PPh3 and LiCl seems to be a key step in this system.
trans-[Pd(Ar)Cl(PPh3)2] complexes were proposed to be
formed when the oxidative addition of the aryl triflate was
carried out in the presence of Cl-.5,18 Furthermore, in the
electrochemical21 and chemical22 reduction of (PPh3)2PdCl2,
anionic species of Pd(0) containing Cl were observed, and
neutral trans-[Pd(Ar)Cl(PPh3)2] complexes were obtained when
the oxidative addition of the triflate was performed with these
species.14
Taking all this into account, in our reactions with
(PPh3)2PdCl2 and DMF after the oxidative addition of 3 to Pd(0),
the complex trans-[Pd(Naph)Cl(PPh3)2] was obtained with or
without the addition of LiCl. If this complex was formed in
any case, the addition of LiCl should not produce an appreciable
effect. Accordingly, we observed that the coupling reaction of
3 was barely affected by LiCl.
Both Pd(PPh3)4 and (PPh3)2PdCl2 have been established to
be effective catalysts for aryl triflate coupling reactions, although
with the latter, faster rates were obtained.3 The complexes
generated by reduction of (PPh3)2PdCl2, with which the oxidative
addition of triflates took place, were also demonstrated to be
more reactive than the complexes of Pd(PPh3)4.14
The cross-coupling reaction of 3 with 1a catalyzed by
(PPh3)2PdCl2 in toluene at 80 °C only afforded 2% of 4; a
substantial amount of the cleavage product 1-naphthol was also
formed (entry 1).15 As a comparison, when 1-iodonaphthalene
was used as a substrate in the same coupling conditions, 4 was
obtained in 85% yield.2g Since the rate of the coupling reaction
largely depends on the solvent, a more polar and coordinating
solvent such as DMF was evaluated. When the reaction was
carried out under the same conditions in DMF at 120 °C, 4
was obtained in 35% yield (entry 7). It has been reported that
polar aprotic coordinating solvents (i.e., DMF, DMPU, HMPA,
and DMSO) can act as ligands for Pd and are able to enhance
significantly the coupling rate with triflates.3b,c In agreement
with this, we observed a more efficient reaction in DMF.
(16) (a) Piers, E.; Friesen, R. W.; Keay, B. A. J. Chem. Soc., Chem.
Commun. 1985, 809–810. (b) Piers, E.; Friesen, R. W. J. Org. Chem. 1986,
51, 3405–3406.
(17) Farina, V.; Krishnan, B. J. Am. Chem. Soc. 1991, 113, 9585–9595.
(18) Jutand, A.; Mosleh, A. Organometallics 1995, 14, 1810–1817.
(19) Amatore, C.; Jutand, A. Acc. Chem. Res. 2000, 33, 314–321.
(20) Farina, V.; Baker, S. R.; Benigni, D. A.; Hauck, S. I.; Sapino, C.
J. Org. Chem. 1990, 55, 5833–5847.
(14) Jutand, A.; Mosleh, A. J. Org. Chem. 1997, 62, 261–274.
(15) Subramanian, L. R.; Hanack, M.; Chang, L. W. K.; Imhoff, M. A.;
Schleyer, P. v. R.; Effenberger, F.; Kurtz, W.; Stang, P. J.; Dueber, T. E.
J. Org. Chem. 1976, 41, 4099–4103.
(21) Amatore, C.; Azzabi, M.; Jutand, A. J. Am. Chem. Soc. 1991, 113,
8375–8384.
(22) Negishi, E. I.; Takahashi, T.; Akiyoshi, K. J. Chem. Soc., Chem.
Commun. 1986, 1338–1339.

Notes
The coupling reaction was also hardly affected by extra PPh3;
Organometallics, Vol. 28, No. 3, 2009 935
Table 2. Pd-Catalyzed Cross-Coupling with 1b and 3 with PPh3,
LiCl, and CuIa
however, the addition of both LiCl and free Ph3P ligand
enhanced the rate of the reaction. One explanation for this
particular effect may be the fact that this combination promotes
the formation of different species of Pd(0) during the in situ
reduction of Pd(II) by the stannane and thus facilitates the rate
of the oxidative addition of the triflate to the Pd(0). The
formation of different complexes of Pd(II) in the oxidative
addition is also likely. It was shown that different organopal-
ladium(II) intermediates could be formed and that these
intermediate ratios depend on factors such as the concentration
of free L, the nature of L, the solvent polarity, the solvent
coordinating ability, the nature of Ar, and the temperature.5 As
the transmetalation step can occur at different rates on one or
more different organopalladium(II) intermediates, the reaction
can change dramatically depending on the factors mentioned.
It is important to notice that the final products of the cross-
coupling reaction could be ligands for the catalyst. Although
the 1-naphthyldiphenylarsine 4 obtained as a product is a more
bulky and less σ-donor ligand than PPh3, it is present in a large
excess. This could be a problem for the scope of the coupling
reaction. To evaluate the effect of an excess of ligand, we carried
out the arsination reaction under the same conditions as
described above (entry 10), with the addition of a large amount
of PPh3 (Pd:L ) 1:40). Under these conditions, 59% of product
4 was obtained (entry 11). On comparison of this result with
that of the previous reaction (entry 10), it is clear that the excess
of a good σ-donor ligand affected the coupling reaction;
nevertheless, it was not to a large extent.
amt of (PPh3)2
PdCl2 (mol %)
entry
solvent
time (h)
product 5 (%)b
1
2
3
4
5
DMF
DMF
toluene
toluene
toluene
1.5
10
1.5
10
24
24
24
24
36
29
25
38
51 (42)
46
1.5
a Reaction conditions: the Ph2P- anion was prepared in liquid
ammonia (300 mL) from PPh3 (1 mmol) and Na metal (2 mmol); then
n-Bu3SnCl (1 mmol) was added. The cross-coupling reaction was
carried out with 3 (0.7 mmol), (PPh3)2PdCl2, PPh3 (Pd:L 1:4), LiCl (3
equiv), and CuI (Pd:Cu ) 1:2) for 24 h at 80 °C when toluene was used
or at 120 °C with DMF. b CG yields and isolated yields in parentheses.
more active catalytic system (entry 4). Nearly the same effect
was observed with longer reaction times (entry 5). In all cases
the conversion of the substrate was almost complete and
different amounts of cleavage product 1-naphthol were formed.
Although the oxidative addition pathway should be the same
in arsination and phosphination reactions, a significant change
occurs in the transmetalation when the organoheteroatom
stannanes vary. The stannane n-Bu3SnPPh2 seems to be less
reactive than n-Bu3SnAsPh2 in the coupling reaction with 3.
However, it should be noted that in this reaction the cross-
coupling product was a strong Pd ligand, and the excess of
ligand in solution produced autoretardation.
In addition, the cross-coupling reaction of 3 with 1c was also
examined. When 3 was allowed to react with 1c in DMF and
with PPh3/LiCl/CuI, the yield of 1-naphthyldiphenylstibine 6
was only 18% (eq 3). When we attempted the reaction in
toluene, the reaction did not proceed. The yield could not be
improved when the reaction was performed under other condi-
tions.
Another important development in Pd-catalyzed cross-
coupling reactions involves the use of Cu(I) as cocatalyst which
improved rates and yields.23 In the presence of CuI, the cross-
coupling reaction with stannane 1a became more efficient and
the conversion of 3 proceeded almost to completion to give 4
in 90% yields (entry 12). As a possible mechanistic explanation
for the copper effect, a preliminary transmetalation from the
organostannane has been suggested.23a However, the copper
effect could also be described by the ligand association
mechanism.23b,e In our reaction both mechanistic explanations
could be valid.23b
Having established the optimal reaction conditions for the
Pd-catalyzed arsination of 3, we studied the reactivity of other
organohetereatom stannanes containing phosphorus (1b) and
antimony (1c) as a transferable group. The results of the cross-
coupling reaction of 3 with 1b (eq 2) are shown in Table 2.
To further study this methodology, we examined the Pd-
catalyzed selenylation reaction with the stannane n-Bu3SnSePh
(2) and 3. The coupling reaction catalyzed by (PPh3)2PdCl2 in
toluene at 80 °C with 3 equiv of LiCl and PPh3 as free ligand
afforded naphthalen-1-ylphenylselenide (7) in only 3% yield.
However, the reaction could be successfully carried out using
DMF as solvent and CuI as cocatalyst, which are the optimal
conditions observed for the arsination reaction. Selenide 7 was
obtained in 70% yield (eq 4).24
When the reaction was carried out under the optimal
conditions found for arsination (DMF/PPh3/LiCl/CuI), and after
oxidation of the obtained phosphine, only a 29% yield of
diphenyl-1-naphthylphosphine oxide (5) was observed (entry
1). Yields did not increase with the addition of 10 mol % of
the catalyst (entry 2). With toluene as solvent in the phosphi-
nation, the coupled product 5 was obtained in 38% yield (entry
3). Nevertheless, the use of 10 mol % of the catalyst led to a
In conclusion, there are two different general conditions for
the cross-coupling reaction with 3 and organoheteroatom
stannanes. Optimization studies revealed that the most effective
conditions for n-Bu3SnAsPh2 and n-Bu3SnSePh stannanes were
(PPh3)2PdCl2/PPh3/LiCl/CuI in DMF. The most effective condi-
tions for the stannane n-Bu3SnPPh2 were the same, except in
toluene. In addition, the results of the reactions of triflate with
(23) (a) Liebeskind, L. S.; Fengl, R. W. J. Org. Chem. 1990, 55, 5359–
5364. (b) Farina, V.; Kapadia, S.; Krishnan, B.; Wang, C.; Liebeskind, L. S.
J. Org. Chem. 1994, 59, 5905–5911. (c) Ye, J.; Bhatt, R. K.; Falck, J. R.
J. Am. Chem. Soc. 1994, 116, 1–5. (d) Han, X.; Stolz, B. M.; Corey, E. J.
J. Am. Chem. Soc. 1999, 121, 7600–7605. (e) Casado, A. L.; Espinet, P.
Organometallics 2003, 22, 1305–1309.

936 Organometallics, Vol. 28, No. 3, 2009
Notes
temperature, (PPh3)2PdCl2 (1.5 mol %), PPh3 (6 mol %), CuI (3
mol %), 3 (1.4 mmol), and DMF (2 mL) were added. When the
solution of 1a was added, the reaction mixture turned deep brown.
The reaction mixture was heated for 24 h in an oil bath at 120 °C.
Water was added to the cold reaction mixture and then extracted
three times with CH2Cl2 (30 mL each). The crude reaction mixture
was treated with aqueous KF (ca. 2 equiv) to eliminate n-Bu3SnI.25
After drying with anhydrous MgSO4, the product 426 was quantified
by CG using the internal standard method, yielding 90% of the
product. The product was isolated from the reaction mixture by
column chromatography on silica gel (hexanes-ethyl acetate),
yielding 82% of 4.
n-Bu3SnSbPh2 indicated the limit of the application of stannanes
of group 15 elements.
It is particularly noteworthy that the products of the arsination
reaction are Pd ligands; nevertheless, the reaction proceeded
almost to completion. In contrast, the phosphination reaction
was more affected, which may be attributed to the fact that
phosphines are stronger Pd ligands than arsines.
The combination of LiCl and free PPh3 ligand was particularly
effective in enhancing the cross-coupling reaction of 3 and
organoheteroatom stannanes with (PPh3)2PdCl2 as catalyst.
These coupling reactions extended the use of organoheteroatom
stannanes in the Stille reaction.
Acknowledgment. We thank the ACC, CONICET, FON-
CYT, and SECYT, Universidad Nacional de Co´rdoba, for
their continuous support to our work. M.B. thanks CONICET
for a fellowship.
Experimental Section
Representative Procedure for Palladium-Catalyzed Cross-
Coupling Reactions with Organoheteroatom Stannanes and
1-NaphOTf (3). The following procedure for the reaction of 3 with
1a is representative of all these reactions. Into a three-necked, 500
mL, round-bottomed flask was condensed approximately 400 mL
of ammonia previously dried with Na metal under nitrogen. AsPh3
(1.0 mmol) and then 2 equiv of Na metal (2 mmol) in small pieces
were added, with a pause for bleaching between each addition. At
20-30 min after the last addition, Ph2As- anion was formed, and
n-Bu3SnCl (2 mmol) was added slowly. The mixture was then
stirred for 5 min and the liquid ammonia was allowed to evaporate.
Evaporation left a white solid residue which was dissolved in dry
DMF (30 mL). This solution was added via cannula and syringe
into a Schlenk tube. In the tube, LiCl (3 equiv) was previously
dried under vacuum at 150 °C for 4 h; after cooling at room
Supporting Information Available: Text and figures giving
general experimental details and procedures and 1H and 13C NMR
spectral data for 4, 5, 6, and 7. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM8009816
(24) Naphthalen-1-ylphenylselenide was isolated in yields ca. 10-15%
lower than those found in CG yield. This yield was not optimized.
(25) Leibner, J. E.; Jacobus, J. J. Org. Chem. 1979, 44, 449–450.
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