Alkynyltins applications

Alkynyltin reagents applications, 9, 360 in Sonogashira coupling, 11, 18 in i/ -hydridized carbon polymerization, 11, 674-675 Alkynyltriphenylbismuthonium salts, in G—heteroatom bond formation, 9, 450... 

A particularly interesting application of this protocol, in conjunction with the direct cross-coupling with terminal acetylenes is shown in Scheme 5-2. Here, the first coupling occurs between the alkynyltin reagent 50 and the cyclized palladium intermediate 49 and is followed by the second direct coupling with the terminal acetylene 52 at the vinyl bromide moiety to yield unsymmetrical cyclic dienediyne 53 [32]. 

In cases where alkynylmetals are generated either in situ or in a separate step as discrete reagents. Mg, Zn, B, and Sn have been the four widely used metals. Comparative studies have shown that Zn is generally the most favorable among them (Sect. III.2.8.2). Here again, however, Sn has been the most frequently used metal. Similar comments on Sn as those made in Sect. D are also applicable to these cases. Particularly noteworthy are examples of the intramolecnlar cyclization of alkynyltins, as in the synthesis of neocarzinostatin. cyclization via double alkynylation with haloalkynes, as in the synthesis of calicheamicinone and dynemicin and... 

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