Preparation of New Nitrogen-Bridged Heterocycles. Synthesis and Some Reactions of 2,3-Dihydroindolizin-2-one Derivatives

Article abstract of DOI:10.1021/jo01313a017

Alkaline treatment of 1-<(ethoxycarbonyl)methyl>-2-picolinium halides 1-5 in ethanol afforded the intramolecular condensation products, 2,3-dihydroindolizin-2-one derivatives 6-10, with the formation of the pyridine base.The possibility of the aromatic enol tautomer for the structures of 6-10 was excluded completely by the inspection of their IR and NMR spectra.The reactions of dihydroindolizinones 9 and 10 and pyridinium salts 1-5 with some alkylating and acylating agents in the presence of alkali gave 3,3-dialkyl- (19-40) and 3-spiro-2,3-dihydroindolizin-2-ones (45-50) and 2-alkoxy- (52, 53, and 57-63) and 2-(acyloxy)indolizines (64 and 65), while those with a bifunctional reagent such as diethyl (ethoxymethylene)malonate afforded tricyclic 2H-pyrano-<2,3-b>indolizin-2-one derivatives 67-69.The mechanisms of the alkylation and the acylation could be well explained by the application of the HSAB principle to the ambident anion generated by the alkaline treatment of 2,3-dihydroindolizin-2-ones 6-10.