TBHP/KI-Promoted Annulation of Anilines, Ethers, and Elemental Sulfur: Access to 2-Aryl-, 2-Heteroaryl-, or 2-Alkyl-Substituted Benzothiazoles

Abstract

An efficient TBHP/KI-promoted annulation of anilines with ethers and elemental sulfur has been developed through the selective C−O bond cleavage of ethers under transition-metal-free conditions. A wide range of 2-aryl-, 2heteroaryl-, and 2-alkyl-substituted benzothiazoles were easily prepared with satisfactory yields and good functional group compatibility.

Recent Advances in the Synthesis of Heterocycles via Reactions Involving Elemental Sulfur

“…[96] When tert-butyl hydroperoxide/KI was added to the reaction mixtures as oxidant, the method could be extended to ether substrates 228 as C-2 precursors (Scheme 77). [97] This system of oxidant was known to oxidize ether into oxonium 230, which was next attack by amino species to provide the corresponding imines 231. Thanks to stronger oxidizing potential of TBHP, further reactions on 230 provided 229 benzothiazoles with wider scope for both C-2 substituents and anilines bearing an electron withdrawing group.…”

Sulfur-Promoted Redox Cyclization of 2,2′-Dinitrodiphenyl Disulfides and Benzylamines

“…Melting points were determined with a YAMATO MP-21 instrument (Yamato Scientific Co., Ltd., Tokyo, Japan) and were uncorrected. 1 H, 13 C, and 19 F NMR spectra were obtained on a JEOL JNM-ECA600 instrument (JEOL Ltd., Tokyo, Japan). 1 H NMR spectra were recorded on a 600 MHz spectrometer using CDCl3 as a solvent referenced to CHCl3 (7.26 ppm).…”

“…Increasing the concentration of 2a did not improve the product yield (entry 10), neither did altering the pyridine concentration give better yields (entries 11 and 12). Changes in the reaction temperature and reaction time also did not improve the yields (entries [13][14][15][16].…”

Recent Advances in Sulfur-Containing Heterocycle Formation via Direct C–H Sulfuration with Elemental Sulfur

“…An efficient TBHP/KI-promoted annulation of anilines with ethers and elemental sulfur was developed through selective C-O bond cleavage of ethers under metal-free conditions (Scheme 44). 74 A wide range of 2-aryl-, 2-heteroaryl-, and 2-alkyl-substituted benzothiazoles were easily prepared with satisfactory yields and good functional group compatibility. This procedure provided an efficient pathway to synthesize the antitumor agent 4-(benzo[d]thiazol-2-yl)-2-methylaniline in one step.…”