Synthesis of phenothiazines from cyclohexanones and 2-aminobenzenethiols under transition-metal-free conditions

Abstract

A convenient method for the synthesis of various substituted phenothiazines from cyclohexanones and 2-aminobenzenethiols using molecular oxygen as hydrogen acceptor in the absence of transition-metals is described. For the first time cyclohexanones were used as coupling partners for the construction of phenothiazines.

Recent Progress in the Construction of S—S, P—S and C—S Bonds Involving O2-Initiated Sulfur-Centered Radicals

“…3.4 硫自由基与 C(sp 3 )-H 键的反应 2013 年, 邓国军课题组 [34] 2017 年, 本课题组 [36] 实现了空气氛围下 1,3-二羰基 化合物的 C(sp 3 )-H 键硫醚化反应(Scheme 32). 在室温 下, 硫酚在碱存在下被氧气氧化为二硫化物.…”

Catalytic dehydrogenative aromatization: an alternative route to functionalized arenes

“…One year later, the same group employed 2-aminobenzenethiols as double-site coupling reagents for the metal free synthesis of phenothiazines (Scheme 20). 33 Various functionalized phenothiazines were successfully synthesised using a combination of benzyl aryl sulfone and potassium iodide under an oxygen atmosphere. Cyclohexanones bearing electron-donating groups at the para position gave the corresponding phenothiazines in good yields with several 2-aminobenzenethiols.…”

Access to Phenothiazine Derivatives via Iodide-Mediated Oxidative Three-Component Annulation Reaction

“…Despite the significant utility, these transformations generally suffer from one or more limitations such as the need for preinstallation steps to access requisite coupling reactants, the use of transition metal catalysts and less environmentally benign halogenated substrates, and low step- and atom-efficiency. To overcome these issues, Deng’s group developed a four-component approach via a key iodide-mediated sulfuration of two β-sites of enamines, arising from the condensation of amines and two molecules of cyclohexanones (eq 3) . However, such a method is more applicable for access to symmetrical phenothiazines.…”