Other Organotin Reagents

Some related reagent, the 2,4-pentadienyltin, was shown to be reactive as well [304]. Propargyltin was equally found to be efficient for transferring an allene group [305]. However, a larger excess of propargyltin is needed, due to the radical isomerization of the propargyltin to the less reactive allenyltin. This was used in the synthesis of modified nucleosides [306]. 

Finally, alkyltins can participate in radical chemistry, especially when the /3-elimination is thermodynamicaly favored, leading, for instance, to carbocyclic ring expansions [313], In a similar way, radical reactions involving a 1,3-stannyl shift could afford 5-exo cyclizations [314]. 

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Organomanganese(II) iodides, 210 Organotin reagents, 211 Organovanadium reagents, 219 From carboxylic acids Benzylchlorobis(triphenylphos-phine)palladium(II), 30 From other acyl derivatives Lithium o-lithiophenoxide, 166 Organomanganese(II) iodides, 210 From 1,2-diols or 1,2-amino alcohols Diethoxy triphenylphosphorane, 109... 

Despite the unique synthetic possibilities offered by organotin reagents, their use in the chemical industry has steadily declined in recent years as a result of perceived toxicity and environmental concerns associated with disposal of tin wastes.30-31 Consequently, appreciable efforts have been made to develop heavy metal-free alternatives based on silicon, germanium, or phosphorus chemistry. Other strategies have been applied to immobilize the tin reagents or to reduce their usage to less than stoichiometric amounts. 

Silver BINAP complex was used as well by Yanagisawa and coworkers . The particular feature of this catalyst is the marked anti selectivity when nsing crotyltins, regardless of whether the donble bond is (E) or (Z). This selectivity is explained by a fast transmetaUation step between the chiral complex and the organotin reagent, followed by the addition on the carbonyl gronp via a cyclic transition state. This reaction has been extended to other organometallics snch as 2,4-pentadienylstannanes . 

Hi. The monomer polymerization route. Compared with the resin-functionalization route, the homo- and copolymerization of organotin-containing monomers permits one to influence the polymer resin structure to a greater extent. In principle, it is possible to prepare gel-type, macroporous, microporous or nonporous polymers. The pore structure, tin loading, solubility and other factors which influence the reactivity of the polymer-supported organotin reagents can be controlled by appropriate... 

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