Discussion
Predict the major product of the following reactions :
- A.
- B.
- C.
- D.
Answer: A
The answer is (A): I is 2-methoxy-2-phenylethanol and II is 2-methoxy-1-phenylethanol.
Acid-catalysed opening (MeOH, H3O+): the epoxide oxygen is protonated, and the C-O bond to the benzylic carbon weakens, because that carbon can carry the developing positive charge. Methanol attacks the more substituted, benzylic carbon, so I has OMe on the benzylic carbon and OH on the CH2.
Base (MeOH, NaOMe): methoxide opens the neutral epoxide by an SN2 attack at the less hindered CH2, so II has OMe on the CH2 and OH on the benzylic carbon.
(B) reverses the two, and (C) and (D) give the same product for both conditions, ignoring the change in regiochemistry.
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