Dipole stabilized carbanions in series of cyclic aldonitrones. Part I. Aldonitrones metallation and dimerization in LDA and n-BuLi solutions.

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.