QuestionOrganic / SN1 at anomeric carbon
The major product(s) formed in the following reaction is/are:
- (a) 2-OMe epimers (both), 3-Br retained
- (b) 3-OMe epimers, 2-Br retained
- (c) cis-2-OMe-3-Br only
- (d) 3-OMe-2-Br only
Answer: (a)
C2–Br sits next to ring O: it ionises easily (oxocarbenium ion, SN1). MeOH attacks the planar cation from both faces → both C2 epimers with OMe; the C3–Br (ordinary 2°) is untouched with 1 equiv. MeOH → (a).