An unprecedented modality for in situ generation of indole-ortho-quinodimethanes from 2-methylindole-based methylenemalononitriles by amine-mediated remote C(sp³)-H deprotonation was developed. These intermediates were efficiently trapped by diverse enals to provide a rapid entry to 2,9-dihydro-1H-carbazole-3-carboxyaldehyde structures via formal asymmetric [4+2] eliminative cycloaddition governed by α,α-diphenylprolinol trimethylsilyl ether catalyst.
Exploiting the Distal Reactivity of Indolyl- methylenemalononitriles: an Asymmetric Organocatalyzed [4+2] Cycloaddition with Enals Enables the Assembly of Elusive Dihydrocarbazoles / Curti, Claudio; Rassu, Gloria; Zambrano, Vincenzo; Pinna, Luigi; Brindani, Nicoletta; Pelosi, Giorgio; Zanardi, Franca. - In: CHEMISTRY-A EUROPEAN JOURNAL. - ISSN 0947-6539. - 22:36(2016), pp. 12637-12640. [10.1002/chem.201602793]