One-Step Synthesis of Hydropyrrolo[3,2-b]indoles via Cascade Reactions of Oxindole-Derived Nitrones with Allenoates

Hydropyrrolo[2,3-b]indole is a privileged indoline motif, while its analogue, hydropyrrolo[3,2-b]indole, has been much less explored. Herein, we developed a cascade reaction of oxindole-derived nitrones with allenoates, providing straightforward access to the tetracyclic hydropyrrolo-[3,2-b]indole scaffolds. Formation of multiple C-C/C-X bonds and cleavage could be achieved within one synthetic step using a simple catalyst (Gimeracil) under mild conditions. The reaction pathway may involve the generation of spiro-hydroazepinone as the key intermediate.

Automated summary

In this study, a straightforward and efficient method for the synthesis of tetracyclic hydropyrrolo-[3,2-b]indole scaffolds was developed through a cascade reaction of oxindole-derived nitrones with allenoates. Multiple bond formations and cleavage could be achieved using a simple catalyst under mild conditions.