Level 2 – Case 31
Stereoselective Synthesis of 2-Acylaziridines
Key point: Stereochemistry. Solvent effects
I(Ph)Br
AcO
n-C 8 H 17
EtOLi
R 1 CH NR 2
N
R 1
n-C 8 H 17
O
R 2
o C
Stereoselective Synthesis of 2-Acylaziridines
The reaction between Z-(2-acetoxyvinyl)iodonium bromides
Z Z
1 and imines 3 in
EtOLi, provides a route for the synthesis of 2-acylaziridines 4 in good yields. It
has been proposed that the first step of the reaction consists in the in situ formation of a monocarbonyl iodonium ylide 2, that adds to the imine to give the corresponding aziridines as cis:trans mixtures (Scheme 31.1).
I(Ph)Br
AcO
n-C 8 H 17
EtOLi
n-C 8 H 17
IPh
O
R
1 CH NR
2
N
R
1
n-C 8 H 17
O
R
2
1
2
3
4
THF, -78
o C
Scheme 31.1
A study of the stereoselectivity of the reaction has demonstrated that the stereochemical outcome of the aziridination depends on the solvent employed. Thus,
when the reaction between 1 and N-(phenylsulfonyl)benzaldimine N N
5 was carried
out in THF, cis-aziridine 6 was stereoselectively obtained. By contrast, transaziridine 6 was isolated as the major reaction product in THF:DMSO (12:1)
(Scheme 31.2).
I(Ph)Br
n-C 8 H 17
AcO
PhCH NSO 2 Ph
EtOLi
N
Ph
n-C 8 H 17
O
SO 2 Ph
, cis:trans 40:60
1
5
THF, cis:trans 70:30
6
Scheme 31.2