Alkenes react with diborane (B2H6) and form trialkyl boranes.
Trialkylboranes then react with H2O2 and give alcohols.
Due to this reaction Propene is converted to alcohol
H3C-CH=CH2 is converted to H3C-CH2-CH2OH
The final result of this raction is the addition of a water molecule to the double bond of the molecule in a direction opposite to that of Markownikov rule.
This reaction was discovered by Herbert C. Brown, who was awared Nobel prize in 1980 for the synthetic use of the reaction.