Solventless Clay-Promoted Friedel−Crafts Reaction of Indoles with α-Amido Sulfones:  Unexpected Synthesis of 3-(1-Arylsulfonylalkyl) Indoles

Abstract

Friedel-Crafts reaction of indoles with alpha-amido sulfones in the presence of montmorillonite K-10 leads unexpectedly to 3-(1-arylsulfonylalkyl) indoles in good yield. The obtained products can be further desulfonylated under reductive or alkylative conditions giving linear and branched 3-substituted indoles.

Rapid and General Protocol towards Catalyst‐Free Friedel–Crafts C‐Alkylation of Indoles in Water Assisted by Microwave Irradiation

“…The NMR spectra of the products 3aa, [8] 3ba, [8] 3ca, [9] 3da, [10] 3fa, [11] 3ha, [12] 3ja [11] and 3ka [13] are in accordance with those in the literature. concentration were screened, and it was found that only a 1.2:1.0 ratio of indole/benzyl bromide was required for an efficient conversion, thereby preventing the use of a large excess of reagents without any concentration influence.…”

“…[d] The NMR spectra of the products 3aa, [8] 3ab, [14] 3ad, [15] and 3ah [8] are in accordance with those in the literature.…”

Ordered organo-inorganic hybrid mesoporous solid acid catalysts (Zr–TMS–TFA) for Michael addition of indoles with α,β-unsaturated carbonyl compounds under environmentally benign solvent free conditions

“…The acid catalyzed reaction of indoles requires careful control of the acidity to prevent unwanted side reactions, such as dimerization and polymerization [41,42]. The clay promoted FriedelCraft alkylation of indole to enone and amido sulfones were also investigated [43,44]. Michael addition of indoles to enones was also investigated over photoinduced 1,4-additions [45].…”

Regioselective Arylations of α‐Amido Sulfones with Electron‐Rich Arenes through Friedel–Crafts Alkylations Catalyzed by Ferric Chloride Hexahydrate: Synthesis of Unsymmetrical and Bis‐Symmetrical Triarylmethanes

“…A plausible mechanism for the formation of 14 may start from the N-acyliminium ion B (Figure 1) formed by elimination of arenesulfinic acid from the α-amido sulfone 13 through the action of the Fe III in FeCl 3 ·6 H 2 O. A reaction between the strong electrophile B and 1,2,4-trimethoxybenzene (9) would then give the Friedel-Crafts product C. Fe III could catalyze the elimination of carbamate from C, leading to the formation of oxonium ion D. [16] The oxonium ion D could then react once more with 1,2,4-trimethoxybenzene (9), giving rise to the bis-arene E through the reversible reaction. The formation of the bis-arene E was observed by TLC (just above the spot for the desired product) during the course of the reaction but had completely disappeared at end of the reaction.…”