Use of Molecular Oxygen as a Reoxidant in the Synthesis of 2‐Substituted Benzothiazoles via Palladium‐Catalyzed CH Functionalization/Intramolecular CS Bond Formation

Abstract

Molecular oxygen (O 2 ) was successfully employed as a reoxidant in cyclizations of thiobenz-A C H T U N G T R E N N U N G anilides 1a-s through a palladium-catalyzed C À H functionalization/intramolecular C À S bond formation process, leading to an efficient, green method for the synthesis of 2-arylbenzothiazoles 2a-s. Addition of cesium fluoride (CsF) greatly enhanced the reactions, which produced variously substituted 2-arylbenzothiazoles with good functional group tolerance. Thioureas 4a-j were also found to be suitable substrates for the cyclization process using a palladium/ O 2 catalyst system, thus generating 2-aminobenzothiazoles 5a-j. One-pot syntheses of 2-aminobenzothiazoles 5a-j from aryl isothiocyanates 6 and amines 7 were also successful.

Reactivity and substituent effects in the cyclization of N -aryl-2-nitrosoanilines to phenazines

“…12 2-Deuterio-4-methoxyanilinene was prepared according to the reported method. 20 Phenazines 2b, 12 2c, 10a 2d, 12 2i, 14 3a, 12 3c, 12 4a 12 and 4c 12 were identical with those obtained and described earlier.…”

Pd‐Catalyzed Synthesis of Other Heteroatom‐Containing Heterocycles

“…They proposed that the mechanism of this reaction undergone electrophilic palladation pathway. A similar work was reported by Doi [15], Kondo [16], and coworkers, respectively. The Pd-and Cu-catalyzed intramolecular C-S linkage of 2-fluoro, 2-chloro, 2-bromo, and 2-iodo aryl thioureas to regioselectively form 2-aminobenzothiazoles was reported by Patel and coworkers (Scheme 4.11) [17].…”

Palladium(II) Acetate as Catalyst for the N-Alkylation of Aromatic Amines, Sulfonamides, and Related Nitrogenated Compounds with Alcohols by a Hydrogen Autotransfer Process

“…The reaction with an electron-poor substituted aniline gave a modest result, but in this case the reason was the aforementioned problem of the dehalogenation process (entry 11). The reaction could be carried out using heteroaromatic systems such as 2-pyridylamine (entries 12-17), 4-pyridylamine (entries 18 and 19), 2-pyrimidylamine (entries 20 and 21), and benzothiazol-2-ylamine (entries [22][23][24][25] following in all cases the tendencies previously found for aniline. It is interesting to point out that the usual alkylation of benzothiazol-2-amine with alkyl halides takes place at the most basic endocyclic nitrogen, affording 3-substituted 2-iminobenzothiazolines as the products.…”