C(sp3)–H Activation Enabled by (η3-Indolylmethyl)palladium Complexes: Synthesis of Monosubstituted Tetrahydrocarbazoles

Abstract

The synthesis of monosubstituted tetrahydrocarbazoles is achieved via the palladium-catalyzed formal [4+2]-cycloaddition of 2-alkyl-3-indolylmethyl carbonates and monosubstituted olefins. The transformation demonstrates an unusual C(sp3)-H activation enabled by (η3-indolylmethyl)palladium complexes. The regioselectivity is found to be dependent on the nature of the substituent across the olefin component. Elaborate mechanistic studies are performed, and the synthetic utility of the products is also demonstrated.

Access to CF3-benzofulvenes via palladium-catalyzed cascade arylation/Trost–Oppolzer cyclization/double-bond isomerization

“…1b). 7 Enthused by these innovative works, we envisioned that the in situ generated olefin from alkyne through a palladium-catalyzed aryl boronic acid addition 8 could undergo intramolecular ASR to give the corresponding carbocycle (Fig. 1c).…”

“…However, finding a suitable palladium catalyst for this reaction is challenging because the single catalyst should work chemoselectively for arylation followed by Oppolzer cyclization. Therefore, in continuation of developing novel methods to furnish fluorinated molecular architectures, 10 herein we have designed and synthesized a suitable substrate and developed a catalytic system for the cascade reactions of arylation, acid-free iso-Nazarov type cyclization, 7,11 and double bond isomerization to access the highly functionalized CF 3 -benzofulvenes in significant yields.…”

“…This transformation represents a rare acid-free iso-Nazarov type cyclization. 7 The intermediate V undergoes β-hydride elimination followed by double bond isomerization in the presence of a base, 9 furnishing the desired CF 3 -benzofulvene 3aa in good yield.…”