Ma. Voinov et al., Dipole stabilized carbanions in series of cyclic aldonitrones. Part I. Aldonitrones metallation and dimerization in LDA and n-BuLi solutions., HETEROCYC C, 4(3), 1998, pp. 261-270
Cyclic aldonitrones (1) under bar (Figure 1) of pyrroline, 3-imidazoline an
d 2H-imidazole series was shown to be lithiated in LDA and n-BuLi ether sol
utions yielding dipole-stabilized carbanions (2) under bar. In the absence
of an "external" electrophile the latter ones react with aldonitrone group
of a non-metallated molecule to give dimer products with the structure depe
nding on the initial nitrone structure. Nitrones with non-conjugated aldoni
trone group <(4a,b)under bar> yield dinitrones <(8a,b)under bar> (Scheme 2)
, whereas conjugated nitrones <(5a,b)under bar> yield iminonitrones <(10a,b
)under bar> (Scheme 3). Acyclic aldonitrone (7) under bar (PBN) does not un
dergo lithiation under the same conditions, which is likely to be due to it
s Z-configuration.