SRN1 and stille reactions: A new synthetic strategy

Article abstract of DOI:10.3390/50300431

The photostimulated reaction of Me₃Sn^- ion with mono, di and trichloro arenes in liquid ammonia gave very good yields of stannanes by the S_RN1 mechanism. These products reacted by a palladium-catalized cross coupling reaction with halobenzenes to give phenylated products also in very goods yields. Similar yields can be obtained in one-pot reactions.

Full text of DOI:10.3390/50300431

431
Molecules 2000, 5
SRN1 and Stille Reactions: A New Synthetic Strategy
Eduardo F. Corsico and Roberto A. Rossi
INFIQC. Depto. de Química Orgánica. Facultad de Ciencias Químicas. UNC. 5000 – Córdoba, Ar-
gentina
E-mail: eduardoc@dqo.fcq.unc.edu.ar
Abstract: The photostimulated reaction of Me3Sn- ion with mono, di and trichloro arenes in
liquid ammonia gave very good yields of stannanes by the SRN1 mechanism. These products
reacted by a palladium-catalized cross coupling reaction with halobenzenes to give phen-
ylated products also in very goods yields. Similar yields can be obtained in one-pot reac-
tions.
Introduction
The radical nucleophilic substitution, or SRN1 reaction, is a process through which a nucleophilic
substitution is obtained [1]. The scope of the process has considerably increased and nowadays it is an
important synthetic possibility to achieve substitution of different substrates. Several nucleophiles can
be used, such as carbanions and anions from compounds bearing heteroatoms, which react to form new
C-C or C-heteroatom bonds in good yields. We thought that the photostimulated reaction of mono-, di-
and trichloro- arenes with Me3Sn- ions in liquid ammonia to synthesize the trimethylarylstannanes
followed by the Pd(0) cross coupling reaction with haloarenes (Stille Reaction) [2,3] would be an im-
portant approach for the synthesis of arylated or polyarylated compounds [4]. Thus, we undertook the
study of the palladium catalyzed reaction of trimethylarylstannanes, synthesized by the SRN1 mecha-
nism, with mono-, di- and trichloro- arenes as a model reaction for this methodology. Also we per-
formed both reactions in one-pot procedures.
Experimental
Organotin compounds were obtained by photostimulated reactions in liquid ammonia. Irradiation
was conducted in a reactor equipped with two 250-W UV lamps emitting maximally at 350 nm. Cross
coupling reactions were carried out with Pd(PPh3)2Cl2 as catalist (3-6%) and DMF as solvent.
Results and Discussion
The photostimulated reactions of Me3Sn- with dichloropyridines, di- and trichlorobenzenes afford di
and tritin compounds in very goods yields:

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Molecules 2000, 5
Me3Sn
Cl
hυ
+ 2 Me3Sn-
SnMe3
Cl
NH3
N
N
2,5: 88%
2,6: 86%
3,5: 80%
The palladium catalized cross coupling reactions of stannanes and aryl halides (PhBr or PhI) gave
the respective arylated compounds:
Cl
i) Me3Sn-
Me3Sn
X
Ph
ii) PhX
Pd (0)
hυ
X
Cl
X
Ph
SnMe3
1 a: X=H, m
2 a: X=H, m (90%)
3 a: X=H, m (97%)
1 b: X=H,
2 b: X=H, (88%)
3 b: X=H, (90%)
p
p
p
1 c: X=Cl, m
2 c: X=Me3Sn, m (71%)
3 c: X=Ph, m (89%)
We also studied the possibility of performing the synthesis of the stannane and the Stille reaction in
a one-pot procedure:
i) Me3Sn-, hυ
1 a
1 b
1 c
3 a: 75 %
3 b: 70 %
3 c: 61 %
ii) PhX, Pd (0)
All these results indicated that the SRN1 mechanism is an excellent method to obtain stannanes by
the photostimulated reactions of mono-, di- and trichloro arenes with Me3Sn- in liquid ammonia. The
stannanes thus obtained can be arylated by further reaction with bromo or iodoarenes through the pal-
ladium catalyzed reactions (or to perform other palladium-catalyzed reactions). Further work is in pro-
gress to examine reactions in a stepwise or one-pot conditions.
Acknowledgements: This work was supported in part by CONICOR, FONCYT AND CONICET. E.C.
gratefully acknowledges receipt a fellowship from Conicet.
References and Notes
1. Rossi, R. A.; Pierini, A. B; Santiago, A. N. In Aromatic Substitution by the SRN1 Reaction, Or-
ganic Reactions Vol. 54; Paquette, L. A.; Bittman, R. Eds.; 1999, p. 1.
2. Stille, J.K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508.
3. Mitchell, T.N. Synthesis 1992, 803.
4. Farina, V.; Krishnamurthy, V.; Scott, W.J, The Stille Reaction, Organic Reactions Vol. 50;
Paquette, L. A., Ed.; 1997.