Synthesis of 3-acylindolizines based on β-nitro-substituted benzochromenes and carbonyl-stabilized pyridinium ylides

3-Acylindolizines containing a (1-hydroxynaphthalen-2-yl)methyl substituent at position 1 were obtained via the reaction of 2-nitro-1H-benzochromenes or 3-nitro-4Hbenzo[h]chromene with carbonyl-stabilized pyridinium ylides. The proposed reaction mechanism includes the Michael addition of the pyridinium ylide, opening of the dihydropyran ring, 5-endo-trig cyclization, and elimination of nitrous acid.