Question

Hydroxylation of cis-2-butene with ${\mathbf{OsO}}_{\mathbf{4}}$yields a different product than hydroxylation of trans-2-butene. Draw the structure, show the stereochemistry of each product, and explain the difference between them.

Short answer

Hydroxylation of an alkene with osmium tetroxide happens with syn stereochemistry. Cis reactant leads to the formation of cis product.The reaction occurs by forming a cyclic osmate intermediate in a single step reaction with an alkene, which on oxidation leads to 1,2 diol.

Oxidation of osmate does not affect the stereochemistry of the carbon-oxygen bond.

Step-by-step solution

Hydroxylation of cis-2-butene with OsO4

Hydroxylation of an alkene with osmium tetroxide happens with syn stereochemistry. Cis reactant leads to the formation of cis product.The reaction occurs by forming a cyclic osmate intermediate in a single step reaction with an alkene, which on oxidation leads to 1,2 diol.

Oxidation of osmate does not affect the stereochemistry of the carbon-oxygen bond.

Hydroxylation of Trans-2-butene with OsO4

Hydroxylation of an alkene with osmium tetroxide happens with syn stereochemistry. Cis reactant leads to the formation of cis product. The reaction occurs with the formation of a cyclic osmate intermediate in a single step reaction with an alkene, which on oxidation leads to the formation of 1,2 diol.

Oxidation of osmate does not affect the stereochemistry of the carbon-oxygen bond.