What is the role of Sharpless Asymmetric Dihydroxylation (SAD) in the synthesis of the CDE ring fragment of pectenotoxin-4?
Label:chem
Topic
After the rhodium-catalysed vinyl 1,4-addition, the resulting 1,1-disubstituted homoallylic alcohol needs to be dihydroxylated to set the stereochemistry at C7. The stereochemical outcome of dihydroxylation of 1,1-disubstituted alkenes can be challenging to predict.
Answer
The Sharpless Asymmetric Dihydroxylation (SAD) is used to control the diol formation with facial selectivity. The choice of ligand in the SAD reaction determines the stereochemistry of the resulting diol, which is critical for the subsequent acid-catalysed cyclisation to form the desired [5,6]-bicyclic ketal structure of the D ring in pectenotoxin-4.
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