The reactions of Me 3 Sn -ion with 2-chloropyridine, pchlorobenzonitrile, o-, m-dichlorobenzenes, 1,3,5-trichlorobenzene, 2,5-, 2,6-, and 3,5-dichloropyridines give good yields of substitution products. When p-bis-(trimethylstannyl)benzene is treated with Na metal in liquid ammonia, a dianion is formed, which upon photostimulated reaction with PhCl, affords the disubstitution product in 70% yield. We suggest that all these reactions occur by the S RN 1 mechanism of nucleophilic substitution.The radical nucleophilic substitution, or S RN 1 reaction, is a process through which a nucleophilic substitution is obtained. The scope of the process has considerably increased and nowadays it is an important synthetic possibility to achieve substitution of different substrates. 1 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. The mechanism is a chain process, whose main steps are presented in Equations 1-3. Equations 1 -3This chain process requires an initiation step. In a few systems, spontaneous electron transfer (ET) from the nucleophile to the substrate has been observed. When the ET does not occur spontaneously, it can be induced by light stimulation. 1 We have previously described the photostimulated reactions of trimethylstannyl ions (Me 3 Sn -) with several chloroarenes in liquid ammonia that afforded substitution products (Equation 4) in very good to excellent yields (70-100%). 2 Many substituents are compatible with the S RN 1 mechanism, 1 and these reactions are an alternative route to the synthesis of stannanes, avoiding the use of Grignard reagents or organolithium compounds. Equation 4The fact that there is no reaction in the dark, but only under irradiation, and that the photostimulated reactions are inhibited by p-dinitrobenzene, indicates that these reactions occur by the S RN 1 mechanism. These reactions can also be carried out in DMSO as solvent under irradiation. 3The S RN 1 reactions of dihaloarenes with nucleophiles afford either the monosubstitution or disubstitution product depending on the structure of the substrate, the nature of the nucleofugal group or the nucleophile. 1 It has been reported that the photostimulated reaction (1 h) of p-dichlorobenzene with Me 3 Sn -in liquid ammonia gives the disubstitution product in 88% yield. 2 We have previously found that the Sn-Me bond in p-anisyltrimethyltin is cleaved with Na metal in liquid ammonia to yield p-anisyldimethylstannyl anion. 4 No products derived from fragmentation of the p-anisyl-tin bond were observed. 5 The photostimulated reaction of p-anisyldimethylstannyl ion with p-chlorotoluene gives (p-anisyl)-dimethyl(p-tolyl)tin in almost quantitative yields. This product was also obtained by a one-pot reaction in an 89% overall yield. 5Now we report the reactions of several chloro-, dichloroand trichloro-substituted substrates with Me 3 Sn -in liquid ammonia, and the preparation of the dianion derived from methyl-tin bond fragmen...
The photostimulated reaction of Me 3 Sn -ion with mono-, di-, and trichloro-arenes in liquid ammonia gave very good yields of stannanes by the S RN 1 mechanism. These products reacted by a palladium-catalyzed cross coupling reaction with halobenzenes to give phenylated products also in very good yields. Similar yields can be obtained in one-pot reactions.For more than a decade, the palladium-catalyzed coupling of organotin compounds with carbon electrophiles, known as the Stille reaction, 1 has been shown to be a very important tool in organic synthesis. 2There are several methods of synthesis for trialkylarylstannanes, typically by the reaction of aryl lithium or organomagnesium derivatives with trialkyltin halides. These reactions have the drawback that many substituents on the aromatic ring are incompatible with the formation of aryl lithium or organomagnesium derivatives. 3 Another approach is the Stille reaction of aryl halides 4 or aryl triflates 5 with hexamethyl-and hexabutyldistannanes. Bis(trimethylstannyl)arenes can also be synthesized using palladium catalysis. Thus, the reaction of 3,5-dibromobiphenyl with hexamethydistannane gave 90% yield of the ditin product; other examples yielded 40-60% yield of disubstitution. 6There are few examples of the reactions of bis(trimethylstannyl)arenes and heteroarenes with aryl halides which afford a double arylation by the palladium cross coupling reaction. Thus, the palladium catalyzed reaction of 3,4-bis(tributylstannyl)furan with bromo or iodoarenes gave 45-85% of diarylation 7 and the reaction of 3-bromopyridine with 2,4-bis(trimethylstannyl)pyridine gave 48% yield of diheteroarylated product. 8 Other examples gave low yields (6-13% yield) of double arylation. 9 As far as we know there is no report of triphenylation on tris(trimethylstannyl) arenes. 2 We have previously described the photostimulated reactions of trimethylstannyl anions which gave very good to excellent yields of substitution products with a number of chloro or dichloro arenes and heteroarenes by the S RN 1 mechanism in liquid ammonia. 10 Many substituents are compatible with the S RN 1 mechanism, such as CO 2 -, CO 2 R, CONR 2 , RO -, -CN, R, aryl, NH 2 , NR 2 , and SO 2 R. Substituents such as -O -or -NO 2 are not suitable, except when arylazo phenyl sulfide are used as substrates. 11 When the substrate has two or three chlorines as leaving groups, it is possible to obtain di and tri substitution products in high yields. 12 We thought that the photostimulated reaction of mono-, di-and trichloroarenes with Me 3 Sn -ions in liquid ammonia to synthesize the trimethylarylstannanes followed by the Pd(0) cross coupling reaction with haloarenes would be an important approach for the synthesis of arylated or polyarylated compounds. Thus, we undertook the study of the palladium catalyzed reaction of trimethylarylstannanes, synthesized by the S RN 1 mechanism, with mono-, di-and trichloroarenes as a model reaction for this methodology. Also we performed both reactions in one-pot procedures.The reaction...
The photostimulated reactions of several mono-, di-, and trichloroarenes and aryltrimethylammonium salts with Me(3)Sn(-) ions in liquid ammonia gave good yields of stannanes by the S(RN)1 mechanism. If the chloroarenes are not soluble in liquid ammonia, diglyme is another solvent to perform these reactions. The stannanes thus obtained can be arylated by further reaction with haloarenes through palladium-catalyzed reactions. If the palladium-catalyzed reaction is performed with a chloroiodoarene as substrate, the stannane reacts faster by the C-I bond via chemoselective cross-coupling reaction to give a chloroarene as product, which can be further arylated by a consecutive S(RN)1-Stille reaction or react with other substrates by another palladium-catalyzed reaction. These sequential reactions can also be performed with substrates with two leaving groups to give products in high yields.
The reactions of trimethylstannyl ions (Me(3)Sn(-)) with vinyl chlorides in liquid ammonia give good yields of vinylstannanes. Some of them react in the dark, and others need light stimulation to react. The fact that these reactions are inhibited by radical and radical anion traps shows that they occur by the S(RN)1 mechanism. When the reaction takes place with 1,1-dichloro-1-alkenes, monosubstitution reduced products are formed in an E/Z mixture. The efficient synthesis of triarylolefins by Pd(0)-catalyzed cross-coupling reactions of vinylstannanes with several iodoarenes is reported. Similar yields were obtained in one-pot-type reactions.
Abstract:The photostimulated reaction of Me 3 Sn -ion with mono, di and trichloro arenes in liquid ammonia gave very good yields of stannanes by the S RN 1 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.
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