Synthesis of arylstannanes from arylamines

Article abstract of DOI:10.1021/om000859p

Arylamines have been converted into aryltrimethylammonium salts, which on reaction with sodium trimethylstannide (1) in liquid ammonia afford aryltrimethylstannanes by the S_RN1 mechanism. With (4-methoxyphenyl)- (2), (1-naphthyl)- (4), phenyl- (6), (4-acetylphenyl)- (8), and (4-cyanophenyl)trimethylammonium salts (10) the substitution products are obtained in good to excellent yields (45-100%). Also, the photo-stimulated reaction of (2-pyridyl)trimethylammonium iodide (12) with 1 leads to the substitution product 13 (50%). With (4-chlorophenyl)trimethylammonium iodide (14) the disubstitution product 19 is obtained in 76% yield. On the other hand, the results obtained in the reaction of (4-bromophenyl)trimethylammonium iodide (15) with 1 clearly indicate a fast HME reaction in the dark. The ET process (S_RN1) competes, although inefficiently, under irradiation.

Full text of DOI:10.1021/om000859p

3
358
Organometallics 2001, 20, 3358-3360
Syn th esis of Ar ylsta n n a n es fr om Ar yla m in es
Alicia B. Chopa,* Mar ´ı a T. Lockhart, and Gustavo Silbestri
INIQO, Departamento de Qu ı´ mica e Ingenier ı´ a Qu ı´ mica, Universidad Nacional del Sur,
Avda. Alem 1253, 8000 Bah ´ı a Blanca, Argentina
Received October 10, 2000
Summary: Arylamines have been converted into aryl-
trimethylammonium salts, which on reaction with so-
dium trimethylstannide (1) in liquid ammonia afford
aryltrimethylstannanes by the SRN1 mechanism. With
Ta ble 1. Rea ction of Ar yl- a n d
Heter oa r yltr im eth yl Am m on iu m Sa lts w ith
a
Me
3
Sn Na in Liqu id NH
3
(Ar)SnMe3 or
(4-methoxyphenyl)- (2), (1-naphthyl)- (4), phenyl- (6), (4-
aryl
conditions;
time (h)
1,4-(Me3Sn)2C6H4,
c
entry
moietyb
yield (%)
acetylphenyl)- (8), and (4-cyanophenyl)trimethylammo-
nium salts (10) the substitution products are obtained
in good to excellent yields (45-100%). Also, the photo-
stimulated reaction of (2-pyridyl)trimethylammonium
iodide (12) with 1 leads to the substitution product 13
1
2
3
4
5
6
7
8
9
4-An
4-An
4-An
4-An
1-naph
1-naph
Ph
dark; 0.5
(4-An)SnMe3, 14
(4-An)SnMe3, 100
0
(4-An)SnMe3, 34
(1-Naph)SnMe3, 85
0
(Ph)SnMe3, 89
0
(4-AcPh)SnMe3, 45
0
(4-CNPh)SnMe3, 100
(4-CNPh)SnMe3, 100
(4-CNPh)SnMe3, 35
(2-Pyr)SnMe3, 50
0
1,4-(Me3Sn)2C6H4, 76
1,4-(Me3Sn)2C6H4, 12
1,4-(Me3Sn)2C6H4, 18
0
hν; 0.5
d
dark; 0.5
hν; 0.5d
hν; 5
(
50%). With (4-chlorophenyl)trimethylammonium iodide
dark; 5
hν; 4
dark; 4
hν; 6
(14) the disubstitution product 19 is obtained in 76%
yield. On the other hand, the results obtained in the
reaction of (4-bromophenyl)trimethylammonium iodide
Ph
4-AcPh
4-AcPh
4-CNPh
4-CNPh
4-CNPh
2-Pyr
1
1
1
1
1
1
1
1
1
1
0
1
2
3
4
5
6
7
8
9
dark; 6
hν; 0.08
(15) with 1 clearly indicate a fast HME reaction in the
dark. The ET process (SRN1) competes, although inef-
ficiently, under irradiation.
dark; 0.08
dark; 0.08d
hν;4
2-Pyr
dark; 4
hν; 5
In tr od u ction
4-ClPhe
4-ClPhe
dark; 5
The SRN1 (unimolecular radical nucleophilic substitu-
4-ClPhe
hν; 5d
1
tion) is a well-known process. The proposed mechanism
e
dark; 5d
4-ClPh
4-BrPhe
4-BrPhe
hν; 5
dark; 5
1,4-(Me3Sn)2C6H4,6
0
f
is a chain process.
20
2
1
Triorganostannyl anions have proved to be excellent
2
a
Substrate/Me SnNa, 1/1.2. b Abbreviations: 4-Anisyl, 4-An;
nucleophiles in SRN1 reactions. We have recently
3
described the photostimulated reactions of haloarenes
and haloheteroarenes with triphenylstannyl anions in
dimethyl sulfoxide and the photostimulated reactions
1-naphthyl, 1-Naph; phenyl, Ph; 4-acetylphenyl, 4-AcPh; 4-cy-
anophenyl, 4-CNPh; 2-pyridyl, 2-pyr; 4-chlorophenyl, 4-ClPh;
4
-bromophenyl, 4-BrPh. c Determined by GC. d 20% p-DNB added.
Substrate/Me3SnNa, 1/2.2. f Together with Me3SnC6H5, 55%.
3
e
of aryldiethyl phosphate esters with trimethyl- and
4
triphenylstannyl anions in liquid ammonia. All these
monia. These reactions are of interest not only from a
mechanistic point of view but also as a suitable synthetic
route to arylstannanes. As far as we know, there are
no reports in the literature concerning the reaction
between triorganotin anions and aryltrimethylammo-
nium salts. The increasing importance of aryltrialkyl-
substrates, under the reaction conditions studied, gave
substitution products in good to excellent yields. The
main advantage of these reactions is that they enable
the direct synthesis of organostannanes with different
1
aryl ligands, avoiding the use of organomagnesium or
organolithium reagents.
stannanes in recent years is connected with their use
A great variety of aromatic compounds with appropri-
ate leaving groups have been shown to react by the SRN1
as substrates in palladium-catalyzed reactions.5
+
mechanism. Various leaving groups, including Me3N ,
Resu lts a n d Discu ssion
1
have been used. We report here the results obtained
in the reactions of a number of aryltrimethylammonium
We have found that there is a slow reaction of
salts with trimethylstannylsodium (1) in liquid am-
(4-methoxyphenyl)trimethylammonium iodide (2) with
1
in the dark, giving the substitution product (4-
*
Member of CIC. To whom correspondence should be addressed.
E-mail: abchopa@uns.edu.ar. Telefax: 54 291 4595187.
1) For reviews see: (a) Bowman, W. R. Chem. Soc. Rev. 1988, 17,
83. (b) Norris, R. K. Comprehensive Organic Synthesis; Trost, B. M.,
methoxyphenyl)trimethylstannane (3) in 14% yield (30
min). On the other hand, when the reaction is carried
out under irradiation, 3 is obtained in quantitative yield
(
2
Ed.; Pergamon: New York, 1991; Vol. 4, p 451. (c) Rossi, R. A.; Pierini,
A. B.; Santiago, A. N. Aromatic Substitution by the SRN1 Reaction:
Organic Reactions; Paquette, L. A., Bittman, R., Eds.; Wiley: New
York, 1999; Vol. 54, p 1.
(30 min) (Table 1, entries 1 and 2). Both reactions are
totally or partially inhibited by the addition of p-
dinitrobenzene (p-DNB) (20%), a well-known inhibitor
of SRN1 reactions (entries 3 and 4).
(2) Yammal, C. C.; Podest a´ , J . C.; Rossi, R. A. J . Org. Chem. 1992,
1
5
1
1
7, 5720.
(3) Lockhart, M. T.; Chopa, A. B.; Rossi, R. A. J . Organomet. Chem.
999, 582, 229.
(5) For a review see: Farina, V.; Krishnamurthy, V.; Scott, W. J .
The Stille Reaction. In Organic Reactions; Paquette, L. A., Ed.; Wiley:
New York, 1997; Vol. 50.
(4) Chopa, A. B.; Lockhart, M. T.; Silbestri, G. Organometallics 2000,
9, 2249.
1
0.1021/om000859p CCC: $20.00 © 2001 American Chemical Society
Publication on Web 06/23/2001

Notes
Organometallics, Vol. 20, No. 15, 2001 3359
Sch em e 1
reaction of (4-cyanophenyl)trimethylammonium sulfate
(10) with 1, either under irradiation or in the dark, led
(
5 min) to quantitative yields of (4-cyanophenyl)tri-
methylstannane (11) (entries 11 and 12). It should be
noted that the spontaneous reaction in the dark
was partially inhibited by the addition of p-DNB (entry
1
3). It can also be observed in Table 1 that (2-pyri-
dyl)trimethylammonium iodide (12) did not react with
in the dark (4 h), but under irradiation the corre-
1
sponding substitution product 2-(trimethylstannyl)piri-
dine (13) was formed in good yield (4 h, 50%) (entries
1
4 and 15). All of these results suggest that the reactions
of 2, 4, 6, 8, 10, and 12 with 1 take place by the SRN1
mechanism.
We have found that also substrates containing two
leaving groups react with 1 under irradiation. Thus, (p-
chlorophenyl)trimethylammonium iodide (14) led after
5
h under irradiation to 1,4-bis(trimethylstannyl)ben-
zene (19) (76%). There is a spontaneous reaction of 14
with 1 in the dark, giving disubstitution product 19 in
1
2% yield. It should be noted that no monosubstitution
product was detected and that the reaction was partially
or completely inhibited in the presence of p-DNB
(entries 16-19). These results clearly indicate that this
disubstituted substrate also reacts with 1 by the SRN1
mechanism, as shown in Scheme 1.
The fact that in this reaction the monosubstitution
product was not detected suggests that the fragmenta-
•-
tion reaction of 17 to give 18 is faster than the electron
transfer (ET) to 14 (Scheme 1, eq 1).
On the other hand, the photostimulated reaction of
(p-bromophenyl)trimethylammonium iodide (15) with 1
led (5 h) to a mixture of disubstitution product 19 (6%)
and phenyltrimethylstannane (7) in 55% yield (entry
2
0). The reaction carried out in the dark gave (5 h) a
mixture of phenyltrimethylammonium salts, and no
substitution product was detected (entry 21). These
results clearly indicate a fast halogen-metal exchange
(
HME) reaction in the dark followed by the protonation
of the intermediate anion 20 by the ammonia to give 6
eq 2). The ET process (SRN1) competes, although
(
Moreover, the photostimulated reactions of (1-naph-
thyl)trimethylammonium iodide (4) and phenyltri-
methylammonium iodide (6) with 1 yield the substitu-
tion products (1-naphthyl)trimethylstannane (5) in 85%
yield (5 h) and phenyltrimethylstannane (7) in 89% yield
(4 h), respectively (entries 5 and 7). It should be noted
that with both substrates no reaction occurred in the
dark (entries 6 and 8). Similar results were obtained
from ammonium salts, supporting different substit-
uents on the aryl moiety. Also, (4-acetylphenyl)trimeth-
ylammonium iodide (8) reacts with 1, leading after 6 h
under irradiation to (4-acetylphenyl)trimethylstannane
inefficiently, under irradiation. Meanwhile, through an
SRN1 mechanism product 19 is formed, as shown in
Scheme 1, the HME mechanism gives 6 as intermediate,
which reacts with 1, leading to 7 through an SRN1
mechanism (eq 4). It should be noted that without
adding water during the workup it was possible to
(9) in 45% yield; there is no reaction between 8 and 1
in the dark (entries 9 and 10). On the other hand, the

3
360 Organometallics, Vol. 20, No. 15, 2001
Notes
isolate trimethyltin iodide as product, probably formed
by an halogen exchange reaction between trimethyltin
bromide and iodide anion.
tions were performed by following the same procedure in all
cases. A 150 mL amount of sodium-dried ammonia was
condensed into a 250 mL three-necked, round-bottomed Pyrex
flask equipped with a cold finger condenser, a nitrogen inlet,
The obtained results demonstrate that the conversion
of arylamines into the corresponding aryltrimethylam-
monium salts followed by the SRN1 displacement with
trimethyltin anions in liquid ammonia is an excellent
and convenient method for the synthesis of arylstan-
nanes. This method has the advantage that various
substituents in the aromatic ring are tolerated. Further
work is in progress to study the scope of the reaction.
3
and a magnetic stirrer. Me SnCl (0.219 g, 1.1 mmol) and Na
metal (0.058 g, 2.53 mmol) were added. When the blue color
disappeared, 2 (0.293 g, 1.00 mmol) was added and then the
mixture was irradiated with stirring for 30 min. The reaction
was quenched by adding MeI in excess, and ammonia was
allowed to evaporate. The residue was treated with water and
then extracted with ether. The products were quantified by
GLC by the external standard method (100%), compared with
4
an authentic sample synthesized by a known procedure.
3
P h otostim u la ted Rea ction of 2 w ith Me Sn Na in th e
Exp er im en ta l Section
P r esen ce of p-DNB. The procedure was similar to that for
the previous reaction, but with the addition of p-DNB (20 mol
%) to the solution of the nucleophile before substrate addition.
Gen er a l P r oced u r es. Irradiation was conducted in a
water-cooled reactor made of Pyrex, equipped with four 250
W UV lamps emitting maximally at 350 nm. Most of the
reagents were available commercially. Ammonium salts were
Ack n ow led gm en t. This work was partially sup-
ported by the Comisi o´ n de Investigaciones Cient ´ı ficas
de la Provincia de Buenos Aires (CIC), the Consejo
Nacional de Investigaciones Cient ´ı ficas y T e´ cnicas
(CONICET), and the Universidad Nacional del Sur,
Bahia Blanca, Argentina. Prof. Carmen N a´ jera is sin-
cerely thanked for her generous gift of some starting
substrates. Special thanks go to Dr. A. E. Z u´ n˜ iga for
obtaining the mass spectra. The CIC is thanked for a
research fellowship to G.S.
6
prepared by known procedures. All the products obtained
were characterized by comparison of their physical, MS, and
NMR spectroscopic characteristics with those of an authentic
2
-4
sample prepared by known procedures.
They were quanti-
fied by GC using the external standard method. The reaction
flask was wrapped with aluminum foil to carry out the
reactions in the dark.
P h otostim u la ted Rea ction of (4-Meth oxyp h en yl)tr i-
m eth yla m m on iu m Iod id e (2) w ith Me
3
Sn Na . The reac-
(6) Sommer, H. Z.; J ackson, L. L. J . Org. Chem. 1970, 35, 1558.
OM000859P