Molecular Iodine-Promoted [3 + 2] Oxidative Cyclization for the Synthesis of Heteroarene-Fused [1,2,4] Thiadiazoles/Selenadiazoles

Abstract

Two new classes of heteroarene-fused [1,2,4]­thiadiazole and [1,2,4]­selenadiazole are synthesized through the iodine-mediated [3 + 2] oxidative cyclization of 2-aminoheteroarenes and isothiocyanates/isoselenocyanates. This oxidative [3 + 2] annulation strategy is highly regiospecific to proceed a selective C–N bond formation at the endo-nitrogen of 2-aminoheteroarenes followed by an intramolecular oxidative N–S/N–Se bond formation. It is the first example of an I2-mediated oxidative nitrogen–selenium (N–Se) bond formation.

Isoselenocyanates: Synthesis and Their Use for Preparing Selenium-Based Heterocycles

“…Scheme 14 Mechanistic studies 70 This result suggests that this reaction does not go through a radical pathway. Thus, a mechanism was proposed with isothiocyanates but can also be further applied with isoselenocyanates.…”

“…In an effort to develop an efficient method, Chen et al reported novel results on their metal-free synthesis of benzimidazole-fused [1,2,4]thiadiazoles from the reactions of 2-aminobenzimidazole and isothiocyanates (ITC), isoselenocyanates (ISC) and isocyanates. 70 Chen's group began with a study of the reaction conditions using 2-aminobenzimidazole (18a) (1.0 equiv) and phenyl isothiocyanate (19a) (2.0 equiv), with different oxidants (0.5-5.0 equiv), bases (3.0 equiv) and solvents over a range of temperatures in order to obtain the desired product, benzo [4,5]imidazo[2,1-c][1,2,4]thiadiazole 20aa (see Table 1). When molecular iodine (0.5 equiv) was introduced as the oxidant, along with K 2 CO 3 (3.0 equiv) as the base and chloroform as the solvent at reflux, the desired product 20aa was obtained in a 40% yield (Table 1, entry 1).…”

“…diazoles via an iodine-mediated [3+2] oxidative cyclization of 2-aminoheteroarenes using both isothiocyanates and isoselenocyanates. 70 The desire for these types of heteroarenes is high as the potential for biological activity can offer a range of therapeutics. This clever protocol utilizes a series of 2-aminobenzimidazole derivatives that are essentially coupled to highly versatile intermediates, such as phenyl, aliphatic and cyclic isoselenocyanates.…”

“…al. reports novel results of their metal-free synthesis of benzimidazole-fused[1,2,4] thiadiazoles from the reaction of 2aminobenzimidazole and isothiocyanates (ITC), isoselenocyanates (ISC) and isocyanates 70.…”

Acid‐Acid‐Catalyzed Tandem Reactions Driven by an Additive‐Like Component

“…These interactions increased partially the reactivities of substrates, thus triggering sequential reaction occur with a specific order. [31] Like NBS, molecular iodine can also assist some oxidative processes, such as the well-known Kornblum oxidation. [32] In view of these excellent performances, molecular iodine was quite often used by organic chemists as a kind of cheap and irreplaceable additive-like component to establish some catalytic systems.…”