Level 1– Case 3
Substrate Selective Reactions in the Presence of
Lewis Acids
Key point: Selectivity t
EWG
R
O
O
EDG
R
Nu
fast
slow
Nu
slow
fast
Lewis acid
Substrate Selective Reactions in the Presence of Lewis
Acids
For an organic chemist it is evident that more electrophilic aldehydes and ketones
1 react with nucleophiles mu m ch faster than less electrophilic analogues 2. However, not as evident is th t e fact that the reverse situation occurs in th t e Lewis acidmediated reactions. That is, more electrophilic aldehydes and ketones 1 react
mu m ch slower th t an the less electrophilic analogues 2 in the presence of a Lewis
acid (Scheme 3.1).
EWG
R
O
O
EDG
R
Nu
fast
slow
Nu
slow
fast
1
2
EWG = electron-withdrawing group
EDG = electron-donating group
Lewis acid
Scheme 3.1
Substrate Selective Reactions in the Presence of
Lewis Acids
Key point: Selectivity t
EWG
R
O
O
EDG
R
Nu
fast
slow
Nu
slow
fast
Lewis acid
Substrate Selective Reactions in the Presence of Lewis
Acids
For an organic chemist it is evident that more electrophilic aldehydes and ketones
1 react with nucleophiles mu m ch faster than less electrophilic analogues 2. However, not as evident is th t e fact that the reverse situation occurs in th t e Lewis acidmediated reactions. That is, more electrophilic aldehydes and ketones 1 react
mu m ch slower th t an the less electrophilic analogues 2 in the presence of a Lewis
acid (Scheme 3.1).
EWG
R
O
O
EDG
R
Nu
fast
slow
Nu
slow
fast
1
2
EWG = electron-withdrawing group
EDG = electron-donating group
Lewis acid
Scheme 3.1