Transition-Metal-Free Synthesis of Nitrogen Containing Heterocycles With Fully Substituted N-fused Pyrrole Rings

The efficient synthesis of C-2 alkylated indolizine, pyrrolo[1,2-a]isoquinoline, and pyrrolo[1,2-a]quinoline derivatives utilizing a single reactivity platform is described. Employing a [3+2] dipolar cycloaddition reaction between heterocyclic N-ylides and allenoates, the incorporation of C-2 alkyl substituents was achieved resulting in various N-fused heterocycles with a fully substituted pyrrole ring. This metal-free route employing allenoates as a dipolarophile solves the longstanding limitations of functional diversity at the C-2 position and the efficient creation of the pyrrolo[1,2-a]quinoline motif.