30
2 The Generation of Nitrile Imine Derivatives
N
N O
O
h
N
N O
O
N
N
N
N O
O
N
N O
O
N
N O
O
N
N
1,3-diazirine
intermediate
R
1 group
migration
Path B
Path A
-CO 2
-CO 2
R
2
R
1
R
2
R
1
R
1
R
2
R
1
R
2
R
1
R
2
R
1
R
1
R
2
R
2
Scheme 2.20 The two hypothesised mechanisms of NI formation via sydnone photolysis
N
N O
O
N
O
SPh
h
PhH
rt
15 %
N
N N
O
O
SPh
O
N
N O
O
t
Bu
h
PhMe
rt, 1.5 h
68 %
N
N
O
O
t
Bu
Scheme 2.21 Unexpected side reactions in the photolysis of some sydnones
2.6 Other Sources
A close structural analogue of the sydnone family, 1,3,4-oxadiazolin-5-ones have
also been documented to generate NIs (Fig. 2.1). This operates through a similar
mechanism to that of the sydnone species, with elimination of CO 2 to yield the