Synthesis of 2-N/S/C-Substituted Benzothiazoles via Intramolecular Cyclative Cleavage of Benzotriazole Ring

Abstract

The synthesis of numerous 2-N/S/C-substituted benzothiazoles was achieved from substituted thiocarbonylbenzotriazoles via free-radical intramolecular cyclative cleavage of the benzotriazole ring in the presence of (TMS)3SiH and AIBN under mild conditions. The developed methodology demonstrates significant compatibility under microwave conditions and is important as it avoids the use of toxic metals for radical cyclization.

A new methodology for the synthesis of N-acylbenzotriazoles

“…[1][2][3][4][5][6][7][8][9] N-acylbenzotriazoles are one of the most useful benzotriazolederivatives which have been successfully utilized to prepare numerous biologically relevant compounds under neutral and mild conditions by N-, C-, S-, and O-acylations. [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24] In recent years our group has been involved in exploration of the synthetic utility of N-acylbenzotriazoles to make sugar amides by N-acylation, 25 benzoxazoles and N-phenylamides by benzotriazole ring cleavage 26,27 and ureas, carbamates and thiocarbamates by the Curtius rearrangement.…”

Recent Developments on Denitrogenative Functionalization of Benzotriazoles

“…However, the reactions of secondary amines (R 2 NH) with bis(1-benzotriazolyl)methanethione furnished the respective N-thioacylbenzotriazoles (R 2 NCSBt) in excellent yields in 30 minutes even in the absence of a base (Scheme 3). 14,15 3 Formation of C-C Bonds…”

“…30 In recent years, benzotriazole derivatives have been employed in inter-and intramolecular cyclizations via a denitrogenative process for the synthesis of various nitrogencontaining fused heterocycles. [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] In 2009, Nakamura and co-workers reported a novel route for the palladium-catalyzed denitrogenative [3+2]cycloaddition of N-aroylbenzotriazoles 1 with internal alkynes 2 for the construction of biologically relevant indole derivatives 3 (Scheme 4). 6 Notable advantages of this novel protocol include a simple, solvent-and base-free experimental procedure, mild reaction conditions, easy separation of the product, the release of molecular nitrogen gas as the sole by-product and satisfactory reaction yields.…”

“…[6][7][8][9][10][11][12][13] On the other hand, intramolecular cyclizations for the synthesis of benzothiazoles and benzoxazoles have been recently reported by the Tiwari group. [14][15][16][17][18][19][20][21]…”

“…Tiwari's group has performed significant research in this field. [14][15][16][17][18][19][20][21] In 2013, we developed a novel protocol for the synthesis of various benzothiazole glycoconjugates from protected carbohydrates through intramolecular cyclization (Scheme 35). 14 This reaction underwent free radical scission of the N-N bond of the benzotriazole ring by treatment with a stannane under heating or microwave irradiation.…”