Various substituted pyrrolo[1,2-a]quinolines
and
pyrrolo[2,1-a]isoquinolines were synthesized in good
to high yields by the Et3N-mediated reaction of push–pull
3-nitrobenzofurans or 1-Ts-/1-Ms-3-nitroindoles and precursors of
carbonyl-stabilized quinolinium and isoquinolinium ylides as 1,3-dipole
equivalents. These transformations proceed in a one-pot manner starting
with the formal [3 + 2]-cycloaddition stage, which is accompanied
by double dearomatization of both quinoline/isoquinoline and benzofuran/indole
moieties, followed by ring-opening of cyclic intermediate formed and
nitrous acid elimination sequence. [3 + 2]-Cycloadducts were isolated
as the final products in cases of impossibility or difficulty of their
enolization. The present protocol was successfully extended to 3-nitro-4H-chromene derivatives as push–pull dipolarophile
component. Finally, using the method of competing reactions, the reactivity
of the starting compounds was compared with each other.