Question

(R)-(+)-Alpine-Borane (Midland Reduction) will reduce acetophenone stereoselectively: (R)-(+)- Alpine-Borane Major Product 1) Please draw the major product for this reaction (take into account stereoselectivity) 2) Please draw both transition states, the favoured and the disfavoured and briefly 3) Which prochiral face of the ketone has been approached by the hydride (si or re) and (1 mark) comment on the reasons why they differ energetically (4 marks) which configuration does the alcohol obtained have (S or R)? (2 marks)

Answer 1

The stereochemical control comes from coordination of the bulky borane to the carbonyl, followed by hydride transfer opposite the largest group.

NOM Ph 3

3. Si phase of ketone is approach by hydride and final alcohol is S.