Tributylstannyl ethers terminal diols

The reactions of tributylstannyl ethers and dibutylstannylene acetals of diols or polyols containing one hydroxyl group that is at the end of a chain (terminal diols) are listed in Table IX. Some reactions on compounds of this type, primarily unprotected glycosides, have been discussed earlier, but for those examples, the terminal hydroxyl group was not critical in... 

From a synthetic point of view, the most important observation is that dibutylstannylene acetals and tributylstannyl ethers can be used to effect terminal substitution of diols in excellent yields, often better than can be obtained by direct reaction at low temperatures, even for benzoylation or p-toluenesulfonylation, where direct reaction is reasonably effective. Terminal O-alkylation, which cannot be performed directly, is routine through choice of the appropriate conditions, as outlined in the sections following. These types of reactions are considered first, followed by reactions where the nonterminal oxygen atom is favored. 

Both tributylstannyl ethers and dibutylstannylene acetals of terminal triols yield in most cases the product of reaction with 1,2-diols in preference to other hydroxyl groups, as shown in Figs. 47 and 48. Figure 47 also illustrates the tendency of t-butylchlorodimethylsilane to react with terminal 1,3-diols in preference to terminal 1,2-diols.87 Figure 48 shows that the preference for reaction at terminal oxygen atoms is considerably stronger than the preference for reaction next to unsubstituted centers, discussed in the previous section. As the numerous examples in Table IX demonstrate, this selectivity is maintained over a wide range of structural features. 

Dibutylstannylene acetals and tributylstannyl ethers of terminal 1,3-diols also react preferentially with most electrophiles on the terminal oxygen atom. The terminal 1,3-diol can be acyclic, or the secondary oxygen atom can be on a ring adjacent to an hydroxymethyl group, such as 0-4 and O-6 of aldohexopyranoses or 0-3 and 0-5 of aldopentofuranoses. Figures 50 to 53 show some examples. 

Fig. 51.—Benzylation of the tributylstannyl ether of a terminal 1,3-diol from a /3-d-glucopyranoside derivative.316...

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