Recently, we found that 3-phenylisoxazole 1 reacts with alkyllithiums with C5-H abstraction followed by ring-opening with formation of a lithium iminoketene intermediate 2. From this, either fragmentation products or compounds (enaminones, pyrimidines) due to further nucleophilic addition of alkyllithiums to the intermediate 2 were formed. According to the proposed mechanism, with non-nucleophilic bases as hindered lithium amides (Scheme) we observed, indeed, a diastereoselective intermolecular cyclization of lithium iminoketene intermediate 2, with formation of a cage-shaped bis-β-lactam 3 as the main product, whose stereochemistry was assigned by X-ray diffraction analysis. This is at variance with the behaviour previously reported for reaction of the same substrate 1 with LTMP, for which isolation of sole fragmentation products was described. Details and a possible mechanism of reaction will be presented and discussed.
Reaction of 3-phenylisoxazole with hindered lithium amides
SCILIMATI, Antonio;VITALE, PAOLA;
2006-01-01
Abstract
Recently, we found that 3-phenylisoxazole 1 reacts with alkyllithiums with C5-H abstraction followed by ring-opening with formation of a lithium iminoketene intermediate 2. From this, either fragmentation products or compounds (enaminones, pyrimidines) due to further nucleophilic addition of alkyllithiums to the intermediate 2 were formed. According to the proposed mechanism, with non-nucleophilic bases as hindered lithium amides (Scheme) we observed, indeed, a diastereoselective intermolecular cyclization of lithium iminoketene intermediate 2, with formation of a cage-shaped bis-β-lactam 3 as the main product, whose stereochemistry was assigned by X-ray diffraction analysis. This is at variance with the behaviour previously reported for reaction of the same substrate 1 with LTMP, for which isolation of sole fragmentation products was described. Details and a possible mechanism of reaction will be presented and discussed.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
