28: Alkene Oxidations
- Page ID
- 150985
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Section: _____________________________
Student ID#:__________________________
Alkene Oxidations: More Pericyclics
Osmate Hydroxylation
Osmium tetroxide (can also be done with KMnO4 or Pb(OAc)4) can hydrolyze an alkene to form a stereospecific 1,2 diol. This reaction sequence is shown below.
- The reaction shown above is a stereospecific oxidation; not all possible stereoisomers are formed. Draw a stepwise mechanism with all arrows clearly shown for the reactions above.
- Predict whether formation of the osmate ester results in a syn or anti addition to the alkene?
- Draw the stereoisomer(s) formed in this reaction.
- Label the above product(s) with the correct R or S designation at each chiral center.
- Draw all of the stereoisomers formed if a-pinene were treated with OsO4.
Ozonolysis
- Draw the Lewis dot structure of ozone (O3).
- Draw the mechanism for ozone reacting with a generic alkene (RCH=CH2).
- The intermediate initially formed in this reaction rearranges to form an ozonide which is then cleaved using dimethyl sulfide. This process is shown below.
Applications:
Ozonolyis is interesting for three reasons:
- Ozonolysis is one of the few C-C bond breaking reactions!
- List all the bond breaking reactions that you know.
- Alkene can be a protecting group for a ketone.
- Show a reaction for making an alkene from a ketone
- Show how you can reverse this reaction.
- Ozonolysis can be used for structure elucidation.
- The corn borer sex pheromone (shown below) was difficult to elucidate because the researchers couldn’t determine the location of the double bond. Explain how ozonolysis and GC-MS could be used to determine location of double bond.
- The corn borer sex pheromone (shown below) was difficult to elucidate because the researchers couldn’t determine the location of the double bond. Explain how ozonolysis and GC-MS could be used to determine location of double bond.