Two-step synthesis of arylstannanes from phenols

Article abstract of DOI:10.1021/om000013l

The reactions of a number of aryl diethyl phosphates (ArDEP) with (triphenylstannyl)sodium and (trimethylstannyl) sodium in liquid ammonia were studied. Results indicate that the conversion of phenols into the corresponding aryl diethyl phosphates followed by the S displacement with organotin anions is an excellent and convenient method for the synthesis of arylstannanes.

Full text of DOI:10.1021/om000013l

Organometallics 2000, 19, 2249-2250
2249
Tw o-Step Syn th esis of Ar ylsta n n a n es fr om P h en ols
Alicia B. Chopa,* Mar´ıa T. Lockhart, and Gustavo Silbestri
INIQO, Departamento de Quı´mica e Ingenierı´a Quı´mica, Universidad Nacional del Sur,
Avda. Alem 1253, 8000 Bah´ıa Blanca, Argentina
Received J anuary 7, 2000
Ta ble 1. Rea ction of Ar yl Dieth yl P h osp h a tes w ith
P h 3Sn Na in Liqu id Am m on ia a
Summary: Phenols are converted into aryl diethyl phos-
phates, which on reaction with alkali-metal triorga-
nostannides in liquid ammonia afford arylstannanes in
excellent yield.
entry aryl moiety conditions, time (h)
ArSnPh3, yield (%)
1
2
3
4
5
6
7
8
9
1-C10H8
1-C10H8
1-C10H8
2-C10H8
2-C10H8
2-C10H8
1,4-C6H4
1,4-C6H4
1,4-C6H4
hν, 4
1-Ph3Sn-C10H8, 66b
hν, 4c
1-Ph3Sn-C10H8, 100b
SRN1 (Unimolecular Radical Nucleophilic Substitu-
tion) is a well-known process.1 The proposed mechanism
is a chain process (Scheme 1). Triorganostannyl anions
have proved to be excellent nucleophiles in SRN1 reac-
tions.2 We have recently described the photostimulated
reactions of haloarenes and haloheteroarenes with
triphenylstannyl anions in dimethyl sulfoxide, which
gave substitution products in good to excellent yield.3
The main advantage of these reactions is that they
enable the direct synthesis of organostannanes with
different aryl ligands,1 avoiding the use of organomag-
nesium or organolithium reagents.
dark, 4
hν, 6
0
2-Ph3Sn-C10H8, 73b
hν, 6c
2-Ph3Sn-C10H8, 100b
dark, 6
hν, 5
0
1,4-(Ph3Sn)2-C6H4, 45e
d
d
d
hν, 2c
1,4-(Ph3Sn)2-C6H4, 70e
dark, 2
hν, 1.5
dark, 1.5
0
d
d
10
11
4-BrC6H4
4-BrC6H4
1,4-(Ph3Sn)2-C6H4,100e
0
a
b
Substrate/Ph3SnNa ) 1/1.2. Determined by GC. c Na metal
added. Substrate/Ph3SnNa ) 1/2.2. e Isolated yield.
d
aryldiethyl phosphate esters. The increasing importance
of arylstannanes in recent years is connected with their
use as substrates in palladium-catalyzed reactions.6
We have found that under irradiation (1-naphthyl)-
DEP (3) reacts with 1 to give the corresponding substi-
tution product, (1-naphthyl)triphenylstannane (5) (4 h,
66%).7 There is no reaction in the dark. It was observed
that the addition of ca. 0.01 g (0.43 mmol) of sodium to
the reaction mixture before irradiation increased the
yield to 100%.8 Similar results were obtained using (2-
naphthyl)DEP (4), which after 6 h led to (2-naphthyl)-
triphenylstannane (6) in quantitative yield (Table 1,
entries 1-6) according to eq 5. These results suggest
that these reactions take place by the SRN1 mechanism.
Sch em e 1
Although halogens are by far the most commonly used
leaving groups in SRN1 reactions, other leaving groups,
including (EtO)2P(O)O,1 have been used.
We report here the results obtained in reactions of a
number of aryl diethyl phosphates (ArDEP)5 with
(triphenylstannyl)sodium (1) and (trimethylstannyl)-
sodium (2) in liquid ammonia. 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
We have also found that substrates containing two
leaving groups react with 1 under irradiation to afford
* To whom correspondence should be addressed. E-mail: achopa@
criba.edu.ar. Telefax: 54-291-4595187.
(1) For reviews see: (a) Bowman, W. R. Chem. Soc. Rev. 1988, 17,
283. (b) Norris, R. K. Comprehensive Organic Synthesis; Trost, B. M.,
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. In
Organic Reactions; Paquette, L. A., Bittman, R., Eds.; Wiley: New
York, 1999; Vol. 54, p 1.
(2) Yammal, C. C.; Podesta´, J . C.; Rossi, R. A. J . Org. Chem. 1992,
57, 5720.
(3) Lockhart, M. T.; Chopa, A. B.; Rossi, R. A. J . Organomet. Chem.
1999, 582, 229.
(4) (Triphenylstannyl)- and (trimethylstannyl)sodium were gener-
ated by the reaction of sodium with the corresponding triorganostannyl
chloride (R3SnCl) in liquid ammonia.2
(5) Phenols were converted into the corresponding aryl diethyl
phosphate esters by the reaction with diethyl phosphite and triethyl-
amine in CCl4 solution. See: Kenner, G. W.; Williams, N. R. J . Chem.
Soc. 1955, 522.
(6) 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.
(7) Irradiation was conducted in a reactor equipped with four 250
W water-cooled UV lamps emitting maximally at 350 nm. The reactions
were performed by following the same procedure in all cases: 200 mL
of sodium-dried ammonia was condensed into a 500 mL three-necked,
round-bottomed Pyrex flask equipped with a coldfinger condenser, a
nitrogen inlet, and a magnetic stirrer. Ph3SnCl (0.92 g, 2.4 mmol) and
Na metal (0.126 g, 5.50 mg atom) were added. When the blue color
disappeared, 3 (0.560 g, 2.00 mmol) was added and then the mixture
irradiated with stirring, for 4 h. 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 product
was quantified by GC using the external standard method, compared
with an authentic sample prepared by a known procedure.3
10.1021/om000013l CCC: $19.00 © 2000 American Chemical Society
Publication on Web 05/18/2000

2250 Organometallics, Vol. 19, No. 12, 2000
Communications
Ta ble 2. Rea ction of Ar yl Dieth yl P h osp h a tes w ith
Me3Sn Na in Liqu id Am m on ia a
Sch em e 2
entry
aryl moiety
conditionsb
ArSnMe3, yield (%)
1
2
3
4
5
6
7
8
4-MeOC6H4
4-MeOC6H4
1-C10H8
hν
dark
hν
dark
hν
dark
hν
dark
Me3Sn(p-anisyl), 81c
0
1-Me3Sn-C10H8, 93c
1-C10H8
4-ClC6H4
4-ClC6H4
1,4-C6H4
0
d
1,4-(Me3Sn)2-C6H4, 97e
d
0
d
1,4-(Me3Sn)2-C6H4, 95e
0
d
1,4-C6H4
a
b
Substrate/Me3SnNa ) 1/1.2. Reaction time: 1 h. c Deter-
mined by GC. Substrate/Me3SnNa ) 1/2.2. e Isolated yield.
d
occurred in the dark (Table 1, entries 7-9). Similar
results were obtained with (4-bromophenyl)DEP (8):
there was no reaction with 1 in the dark, but under
irradiation the disubstitution product 12 was obtained
in quantitative yield (Table 1, entries 10 and 11). All
these results clearly indicate that these disubstituted
substrates also react with 1 under irradiation by the
SRN1 mechanism, as shown in Scheme 2.
The fact that in these reactions monosubstitution
products were not detected suggests that the fragmen-
tation reaction of 10•- to give 11 is faster than the
electron transfer (ET) to 7 or 8 (Scheme 2, eq 6).
The reactions between 2 and various ArDEP esters
gave similar results.
In Table 2 it can be observed that (4-methoxyphenyl)-
DEP (13), 3, (4-chlorophenyl)DEP (14), and 7 did not
react with 2 in the dark (1 h) (entries 2, 4, 6, and 8),
but under irradiation the corresponding substitution
products (4-methoxyphenyl)trimethylstannane (15),10
(1-naphthyl)trimethylstannane (16)11 and 1,4-bis(tri-
methylstannyl)benzene (17)11 were formed in high yield
(81%, 93%, 97%, and 95%, respectively) (entries 1, 3, 5,
and 7). No monosubstitution products were detected in
the reaction of 14 and 7. These results suggest that
these reactions also occur through an SRN1 mechanism.
The obtained results demonstrate that the conversion
of phenols into the corresponding aryl diethyl phos-
phates followed by the SRN1 displacement with organo-
tin anions is an excellent and convenient method for the
synthesis of arylstannanes. This method has the ad-
vantage that both operational steps can be performed
at moderate temperature and various substituents in
the aromatic ring are tolerated. Further work is in
progress to study the scope of the reaction.
Ack n ow led gm en t. This work was partially sup-
ported by the Comisio´n de Investigaciones de la Pro-
vincia de Buenos Aires (CIC), the Consejo Nacional de
Investigaciones Cient´ıficas y Te´cnicas (CONICET), and
the Universidad Nacional del Sur. The CIC is thanked
for a research fellowship to G.S.
disubstitution products in good to excellent yield. Thus,
1,4-bis(diethylphosphono)benzene (7) led after 5 h to 1,4-
bis(triphenylstannyl)benzene (12;9 45%). Stimulation by
the addition of sodium increased the yield to 70% after
a 2 h reaction time. It is to be noted that no monosub-
stitution product was detected and that no reaction
OM000013L
(8) An alkali metal dissolved in liquid ammonia exists for the most
part as alkali-metal cations and solvated electrons and is effective in
provoking SRN1 reactions. See: Dye, J . L. Acc. Chem. Res. 1968, 1,
306.
(10) Quantified by GC by comparison with an authentic sample
prepared according to: Eaborn, C.; Hornfeld, H.; Watson, D. R. M. J .
Chem. Soc. B 1967, 1036.
(11) NMR spectroscopic data are in agreement with those reported
(9) Quantified by GC by comparison with an authentic sample.3
in the literature.2