Nitrile Oxides, Nitrones, and Nitronates in Organic Synthesis : Novel ...

O
Ph
S
124
NMe
NO2
O
Ph
S
Et3N
ArNCO
NMe
O
Ar = p-ClC6H4 R = Ph,Me
MeN MeN
N
O
−78°C N
O
125 126
N
Ar
127
R
REACTIONS OF NITRILE OXIDES 45
Ph-S-CH=N O
Ph-S-C
O OCONHAr
RLi
N
O
Scheme 1.25
O
N
Ar
128
O
N
O
+ PhSONHMe
1.3.4.2. Intermolecular Cycloaddition at C=X orX=Y Bonds Cycloaddition
reactions of nitrile oxides to double bonds containing heteroatoms are well documented.
In particular, there are several reviews concerning problems both of
general (289) and individual aspects. They cover reactions of nitrile oxides with
cumulene structures (290), stereo- and regiocontrol of 1,3-dipolar cycloadditions
of imines and nitrile oxides by metal ions (291), cycloaddition reactions of
o-benzoquinones (292, 293) and aromatic seleno aldehydes as dipolarophiles
in reactions with nitrile oxides (294).
1.3.4.2.1. Aldimines, Ketimines, and Related Compounds as Dipolarophiles
Reactions of aldimines with nitrile oxides proceed readily to give 1,2,4oxadiazolines
independently of the nature of substituents both in dipole and
dipolarophile molecules. 1,2,4-Oxadiazolines were prepared by the regiospeciÞc
1,3-dipolar cycloaddition of nitrile oxides with ßuoro-substituted aldimines
(295). Phosphorylnitrile oxides gave with azomethines, PhCH:NR, phosphorylated
1,2,4-oxadiazolines 129 (296). Expected 1,2,4-oxadiazolines were also
obtained from azomethines, derived from 4-formylcoumarine (179) and 1,3diphenylpyrazole-4-carbaldehyde
(297).
O
N
O
N
Ar
O