Aryl with aryltrialkylstannanes

Pinhey also pioneered the use of arylboronoic acids in a similar transformation which is also catalysed by Hg(OAc)2 [81]. Although the isolated yields for the aryllead triacetates obtained via this method are generally lower that with aryltrialkylstannanes the commercial availability of a large variety of arylboronoic acids make this a very desirable approach. The lower yields can be circumvented somewhat by generation of the aryllead triacetate in situ which has proved to be a successful approach. For example, the in situ generation of a range of aryllead triacetates such a 4-trifluoromethylphenyl, 2-methoxyphenyl and 3-nitrophenyl derivatives were used in the arylation of a P-keto ester (Scheme 4.38) [81]. 

Much of the recent interest in the arylstannanes, particularly the aryltrialkylstannanes, however, derives from their use in the Stille reaction in which an aryl-C bond is generated by reaction with a halide or sulfonate RX, where R = vinyl, allyl, benzyl, or aryl, to give Ar-R under catalysis by palladium68 or another transition metal.69-72 The reactions are very tolerant of various functional groups, and are finding wide application in organic synthesis, and are considered in Section 22.2. 

Because a wide range of aryltrialkylstannanes are available from the corresponding aryl bromides this reaction can be used to introduce one or more dialkylaminomethyl groups into a variety of aromatic substrates. The reaction of A(,N-dimethylmethyleneiminium chloride with l,4-bis(trimethylstannyl)benzene gives IVjVA A -tetramethyl-l, 4-diaminobenzene in 58% yield. ... 

Coupling reactions of organomanganese reagents with 2- and 3- furoyl chloride in the presence of copper or iron catalysts have been used to prepare a number of naturally occurring ketones in high yields <92TL5245> and aryltrialkylstannanes have been shown to arylate 2-furoyl chloride in the presence of a palladium catalyst <92CC1440>. 

In similar manner, hexaalkyldistannanes allow the homo-coupling reactions of aryl iodides, bromides [104] and triflates [105] to the symmetrical biaryls. First, the aryltrialkylstannane is generated by reaction of the aryl halides with Me6Sn2 or -BugSn2, followed by the in situ Stille reaction with an excess of electrophilic reactant, since both reactions are catalysted by the same complexes and proceed at comparable reaction rates. For instance, 2-naphthyl triflate (165) was coupled to 2,2 -binaphthalene (166) in 69% yield [105], respectively, Scheme 22. 

The aryltrialkylstannanes obtained by above described methods affected the Stille cross-coupling reactions whose efficacy is presented through the following examples where arylstannanes 172-176 were reacted with aryl halides 25, 177, 178 and iodobenzene giving biaryls 179-183 in respective yields [77], Scheme 25. 

Synthesis of aryltrialkylstannanes by reaction of aryl bromides with hexaalkyldistannanes Preparation of 2-nitrophenyltrimethylstannane (228) 199]... 

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