Decaborane acetals

Hydroboration is faster than cleavage with borane, but H2BCI etherate cleaves unsaturated acetals without giving hydroboration (equation 10). Lower yields are obtained with the less reactive Me2S complex, but that reagent gives good yields of dihydroxy diethers from chiral bisacetals (equation 11). The diethyl acetal of benzaldehyde can be reduced to ethyl benzyl ether in moderate yield by decaborane in toluene at 120-130 C (equation 12). °... 

Decaborane in aqueous THF, >92% yield. The method only works for acetals that are electron-rich. Aromatic acetals with electron withdrawing groups fail to react thus providing some chemoselectivity. Decaborane can also be used for the formation of dimethyl acetals. 

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