To obtain information about the effect that
methanesulfonamide has in the hydrolysis step in Sharpless asymmetric dihydroxylation, a series of aliphatic and conjugated aromatic
olefins were dihydroxylated with and without
methanesulfonamide. The hypothesis in this study was that
methanesulfonamide is a cosolvent that
aids in the transfer of the
hydroxide ions from the water phase to the organic phase. A plot of t90% versus the computational partition coefficient clog P of the intermediate osmate
ester of nonterminal aliphatic
olefins revealed that the polarity of the intermediate osmate
ester has a significant effect on the reaction time and
methanesulfonamide effect. The more polar the intermediate osmate
ester, the faster is the reaction without
methanesulfonamide and the smaller the accelerating
methanesulfonamide effect.
Methanesulfonamide had no accelerating effect in the asymmetric dihydroxylation of short chain terminal aliphatic
olefins as a result of easier accessibility of terminal osmate
ester groups to the water phase. A cosolvent hypothesis was found not to be valid in asymmetric dihydroxylations of conjugated aromatic
olefins. In the reaction conditions used in Sharpless asymmetric dihydroxylation, weakly acidic
methanesulfonamide was found to be a general
acid catalyst that protonates the intermediate osmate
esters of conjugated aromatic
olefins in the hydrolysis step.