Level 1 – Case 8
52
O
H
Ph
D
H
COOEt
Me
H
COOEt
H
D
Ph h
N
O
H
Me
H
H
H
N
COOEt C
D
OH
Me
Ph
H
H
N
Ph
COOEt
D
O
Me
H
H
N
O
Ph
O
Me
H
D
H
G
G
5
6
13
Scheme 8.8
Obviously the concerted addition step is not possible when the nucleophile is
O-methylhydroxylamine due to the absence of a proton attached to the oxygen
atom. This fact would explain the lack of reactivity observed when O-methylhydroxylamine was employed as reagent.
In Summary
While nucleophilic additions toҏ C=C bonds in D,E-unsaturated systems usually
take place in a conjugated fashion and through mechanisms involving polar transition states, in some cases a concerted addition of the nucleophile must be considered. The addition of hydroxylamines to ethyl cinnamate is a clear example of
such an unusual type of reaction.
Questions
Based on the concerted mechanism previously discussed, try to predict the stereochemistry of the isoxazolidinones obtained in the reaction between deuterated N- N N
methylhydroxylamine and esters 14 and 15.
COOEt
O
O
O
O
COOEt
E-isomer E E
14
Z-isomer
15