SRN1 and Stille Reactions: A New Synthetic Strategy

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 phenylated products also in very goods yields. Similar yields can be obtained in one-pot reactions. 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-, diand trichloroarenes 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 important 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 mechanism, with mono-, diand trichloroarenes as a model reaction for this methodology. Also we performed 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, diand trichlorobenzenes afford di and tritin compounds in very goods yields: Molecules 2000, 5 432 The palladium catalized cross coupling reactions of stannanes and aryl halides (PhBr or PhI) gave the respective arylated compounds: We also studied the possibility of performing the synthesis of the stannane and the Stille reaction in a one-pot procedure: All these results indicated that the SRN1 mechanism is an excellent method to obtain stannanes by the photostimulated reactions of mono-, diand trichloro arenes with Me3Sn in liquid ammonia. The stannanes thus obtained can be arylated by further reaction with bromo or iodoarenes through the palladium catalyzed reactions (or to perform other palladium-catalyzed reactions). Further work is in progress 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, Organic 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. N Cl + 2 Me3Sn NH3 hυ N SnMe3 Me3Sn Cl 2,5: 88% 2,6: 86% 3,5: 80% 1 a 3 a: 75 % 1 b 3 b: 70 % 1 c 3 c: 61 % i) Me3Sn , hυ ii) PhX, Pd (0) Cl Cl