Level 2 – Case 31
208
(DN = 38.8 kcal mol
–1
l l ). The higher the donor number, the stronger is the interac1
tion between solvent and acceptor.
H
H
IPh
O
H
R
C NSO 2 Ph
Ph
H
DMSO
Ph
Ph h h
ROC
Ph
I
H
I
COR
H
Ph
N
S O
Ph
O
N
S O
Ph
O
R
O
IPh
H
NSO 2 Ph
Ph
H
Ph
H
R
O
IPh
H
NSO 2 Ph
R
H
Ph
N
H
O
SO 2 Ph
N
H
SO 2 Ph
Ph
H
O
R
18
G
G
G
G
G
major
2
5
17
cis-aziridine 6
trans-aziridine 6
R = n-C 8 H 17
G
Scheme 31.9
An argument in favor of the role of the sulfon f f yl oxygen atom in the contr t ol of
the stereoselectivity of the reaction is the fact that the aziridinization of N- N N
benzoylimine 7 leads almost exclusively to the trans-aziridine 8 either in THF or
in THF:DMSO mixtures. Following the previous reasoning, now the coordination
between the carbonyl oxygen atom with the iodine (III) is not possible and the
most favorable transition state for the nucleophilic addition step will be the less
crowded, with bulky PhI
+ and benzoyl groups placed antiperiplanar. Transition
state 19 should be more stable than more crowded 20 leading preferentially to
trans-aziridines 8 as major reaction products (Scheme 31.10).
H
H
I
H
ROC
Ph
N
O
Ph
R
IPh
O
C NCOPh
Ph
H
Ph
Ph
N
H
O
R
H
Ph
COPh
I
COR
H
Ph
N
O
Ph
20
19
G
G
G
G
G
G
2
7
more crowded
favored
cis-aziridine
trans-aziridine 8
Scheme 31.10