Regioselectivity 1,2,4-triol acetalization

An important polyalcohol for regioselective acetalizations is the triol of Figure 9.18 because it can be easily obtained from S-malic acid. This substrate contains both a 1,2-diol and a 1,3-diol. Each of these subunits can be incorporated into an acetal selectively—depending on the carbonyl compound with which the acetalization is carried out ... 

Fig. 9.18. Regioselective acetalizations of a 1,2,4-triol ("malic acid triol").

The above kinetically controlled regioselectivity is also reflected in the selective monosilylation of butane-1,2,4-triol. In this case, the sole product obtained is 4-r-butyldimethylsiloxy-butane-l,2-diol with 99% yield (eq 28). The authors rationalized that, with the bulky TBDMSCl, the dibutylstannylene acetal rapidly migrates between the 1,2-diol and 1,3-diols and affords the product of kinetic control. This sequence of reactions was also used to selectively block the equatorial alcohol of a cw-diol on the pyranoside ring... 

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