Syn Dihydroxylation (OsO₄): Making cis-1,2-Diols (Mechanism + Stereochem)

Step-by-step OsO4 dihydroxylation mechanism. Cyclic osmate ester, why addition is syn, and common exam traps (oxidative cleavage conditions).

• Reaction: Alkene → cis-1,2-diol
• What it does: Adds two OH groups syn across a double bond
• Typical reagents: OsO4 (cat.) + NMO, then NaHSO3/H2O
• Key intermediate: Cyclic osmate ester
• Driving force: Concerted addition; reoxidation of Os in catalytic versions
• Exam type: Stereochemistry
• Exam type: Reagent selection
• Exam type: Predict product