Stereodivergent addition of 4-silyloxy-1,2-allenes to aldehydes by hydroboration.

All-ene one! Three out of four stereoisomers of 2-vinyl-1,3-diols can be obtained from a single allene. A simple variation of the reaction conditions modifies the stereochemical outcome of the addition of an allene to an aldehyde via hydroboration. Stereocontrol is dependent upon the order in which the reagents are mixed (leading to E or Z boron species) and the type of aldehyde (aliphatic or aromatic) used.