Reactions dialkylstannylene acetals

Two types of tin derivatives have been used mainly to achieve these reactions dialkylstannylene acetals are formed by reaction of dialkyltin oxides with diols tributyltin ethers are formed by reaction of bis(tributyltin) oxide with alcohols. Some aspects of the regioselectivity achieved with these two types of intermediates are the same, while others are different, as will be outlined in the sections to follow. Where the reaction outcomes are similar, the dialkyltin reagents are strongly preferred because of their lower toxicity. As these reagents are heavily employed, the topic has been reviewed several times, but siguilicant uew observatious continue to be made. This chapter is not intended to be a comprehensive summary of all applicatious of these intermediates, but will highlight examples of each type of selectivity. 

Dialkoxydialkyl stannanes cross-couple with derivatives of chiral tartaric acid, preserving the original chirality, as shown in reaction 32. The dialkylstannylene acetals produced in this reaction are useful reagents for synthesis of chiral compounds28611. 

If p-toluenesulfonylation occurred under these conditions, the product distribution would depend on [R X]. Changing the concentration of p-toluenesulfonyl chloride from 0.10 M to 1.2 M did not affect the product ratio in a reaction with a dialkylstannylene acetal of methyl 2,3-0-isopropylidene-D-mannofuranoside. This result provides additional evidence that this reaction and all slower reactions occur under conditions where equilibration is faster than reaction. 

Scheme 5.1.12 The influence of the structure of the alkyl group on the regioselectivity of p-toluenesulfonation reactions on dialkylstannylene acetals of a hindered terminal-1,2-diol" ...

Many aspects of the regioselective manipulation of polyols through dialkylstannylene acetals have been studied and some interesting modifications have improved this procedure [53, 55], For example, the regioselective formation of monobenzyl, monoallyl and monomethyl ethers, which normally proceeds at very slow speed, is markedly enhanced when the reaction of benzyl and allyl bromides or methyl iodide on dialkylstannylene derivatives of polyhydroxy compounds is carried out in the presence of stoichiometric amounts of quaternary ammonium halides [37,56,57]. Several examples of this modified procedure, such as the regioselective mono-O-alkylation of disaccharide glycosides (Scheme 2), have been reported [58]. 

---