Discussion
The major product formed in the following reaction is :
- A.
- B.
- C.
- D.
Answer: A
The product is the 2,3-epoxy alcohol A, (2R,3R)-2,3-epoxygeraniol.
Sharpless asymmetric epoxidation with Ti(OiPr)4, a tartrate and t-BuOOH works only on allylic alcohols, because the substrate's OH must bind to titanium. Geraniol has two trisubstituted alkenes, but only the C2=C3 bond is allylic to the OH, so only that bond is epoxidised and the remote 6,7-alkene is untouched. That rules out C and D.
The tartrate decides the face. L-(+)-DET gives (2S,3S)-epoxygeraniol, and D-(−)-DET, used here, gives the enantiomer, (2R,3R), which is the structure with the epoxide oxygen wedged as drawn in A. B is the (2S,3S) epoxide from (+)-DET.
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