Palladium‐Catalyzed Intramolecular Sulfonamidation/Oxidation of Imines: Access to Multifunctional Benzimidazoles

Abstract

O-Sulfonamidophenylimines undergo intramolecular sulfonamidation/oxidation to produce 1,2-disubstituted benzimidazoles upon treatment with palladium(II) chloride/(diacetoxyiodo)benzene and potassium carbonate at room temperature. The substituent scope at the 2-position of the benzimidazole can be extended to alkyl, aryl, alkenyl, acyl, and ester functional groups under mild conditions.

Copper‐Catalyzed Mild Nitration of Protected Anilines

“…Interestingly, heterocyclic product 103 is well-suited for a subsequent nitration reaction under our Cucatalyzed methodology, occurring selectively at the para-position with regard to the NH group, as illustrated in the preparation of product 106 (77 % yield). Additionally, the Pd II -catalyzed cyclization through the cascade sulfonamidation-oxidation of the glyoxalate-derived imine 107, [19] obtained in situ from condensation of aniline 101 with ethyl glyoxalate, led to the formation of the benzimidazole derivative 108 in reasonable yield (52 % over two steps).…”

An Intramolecular C(sp2)–H Amidation Using N‐Iodosuccinimide

“…Facilitating the dehydrogenative C(sp 2 )–H amidation reaction. a) Zeng's Pd‐catalyzed intramolecular amidation in the presence of PIDA as an oxidant . b) The iodine(III)‐mediated Pd‐free approach .…”

“…[33] In Zeng's Pd-catalyzed intramolecular amidation in the presence of PIDA as an oxidant, toluene was used as the solvent and the reaction was run for 16 h (Figure 2a). [34] Interestingly, similar reactions could be carried out in the absence of any Pd catalyst in the presence of PIDA under base-free [35] conditions. The reaction time decreased dramatically to <30 min when the solvent was changed to the fluorinated solvent TFE at room temperature ( Figure 2b).…”

“…None of the non-fluorinated solvents tested, including MeCN (acetonitrile), CH 2 Cl 2 (dichloromethane), DCE (1,2-dichloroethane), THF (tetrahydrofuran), DMF (N,N-dimethylformamide), ethyl acetate, EtOH (ethanol), acetone, 1,4-dioxane, nitromethane, etc., gave better results than TFE ( [34] b) The iodine(III)-mediated Pd-free approach. [29] c) Work on amidation using NIS as a mild oxidant.…”

“…Thin‐layer chromatography (TLC) was carried out on Merck silica gel F254 plates (0.25 mm). All starting materials ( N ‐substituted imines 1 ) were prepared by following a literature procedure …”