One-Pot Synthesis of 2-(Indolizin-2-yl)benz-imidazoles from Quinoxalinones

Significance

Reported is a synthesis of 2-(indolizine-2-yl)benzimidazoles from 3-(2-chloroalkyl)-quinoxazolinones in boiling α-picoline. The proposed mechanism involves an N-alkylation of α-picoline followed by intramolecular cyclization resulting in spiro-compound 2, which was isolated in 10-41% yield depending on the R substituent. Subjection of 2 to further heating results in an intramolecular cyclization-rearrangement to 2-(indolizin-2-yl)benzimidazoles 3 in good preparative yields. The structures of 2 and 3 were confirmed by single-crystal X-ray structure analysis. The scope of this interesting reaction was studied incompletely.