Reaction of carbon nucleophiles with alkylideneindazolium and alkylideneindolium ions generated from their 3-(1-arylsulfonylalkyl) indazole and indole precursors

Abstract

Lewis acid promoted elimination of p-toluenesulfinc acid from sulfonyl indazoles and sulfonyl indoles generates the corresponding iminium ion that reacts with allyltin reagents, silyl enol ethers, silyl ketene acetals and electron-rich aromatics leading to functionalized indazole and indole derivatives.

Sulfonyl Azoles in the Synthesis of 3-Functionalized Azole Derivatives

“…For preliminary trials, the allylation reaction was attempted on sulfonyl indazole 65 using allyltributyltin as a nucleophile in the presence of different Lewis acids ( Table 2). [63] Surprisingly, TiCl 4 and SnCl 4 , which were the most effective acids with a-amido sulfones, gave poor results in this reaction ( Table 2, entries 1 and 2). The utilization of AlCl 3 showed a more promising result and, by tuning the acidity level through introducing alkyl substituents at the metal center, we finally found that AlEtCl 2 was the best promoter for our process ( Table 2, entries 3 and 4).…”

“…Although the allyl moiety was amenable to further synthetic manipulations at the double bond, we sought a more direct introduction of useful functional groups through the utilization of weak nucleophilic reagents compatible with the employed Lewis acid, such as silyl enol ethers, silyl ketene acetals, and electron‐rich aromatic compounds (Scheme ) 48,63. All of these nucleophiles were effective, leading to valuable functionalized indazole and indole derivatives 69 in satisfactory yields.…”

Synthesis of indazole motifs and their medicinal importance: An overview

“…Lewis acid promoted elimination of p-toluenesulfonic acid from sulfonyl indazoles and sulfonyl indoles generates the corresponding iminium ion that reacts with allyltin reagent, silyl enol ethers, silyl ketene acetals and electron-rich aromatics leading to the synthesis of indazole derivatives (Scheme-74) [88].…”

Regioselective Synthesis of 3‐Substituted Pyrroles by Nucleophilic Addition of 3‐(1‐Arylsulfonylalkyl) Pyrroles Activated under Basic or Acid Conditions

“…[10] Acidic reagents (Lewistype) are also able to remove the arylsulfinic group from 1 leaving an iminium ion 2 b, which can react with weak nucleophiles thus generating the substituted products 3. [11] An iminium ion structurally related to 2 b is supposed to be active in the indium-catalyzed procedure involving reaction of N-alkyl pyrroles.…”