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Thursday, 7 September 2017

Metal-free oxidative cyclization of 2-aminobenzothiazoles and cyclic ketones enabled by the combination of elemental sulfur and oxygen

Metal-free oxidative cyclization of 2-aminobenzothiazoles and cyclic ketones enabled by the combination of elemental sulfur and oxygen

Green Chem., 2017, Advance Article
DOI: 10.1039/C7GC02014G, Communication
Yanjun Xie, Xiangui Chen, Zhen Wang, Huawen Huang, Bing Yi, Guo-Jun Deng
Aerobic cyclization of 2-aminobenzothiazoles and cyclic ketones enabled by the combination of elemental sulfur and oxygen under metal-free conditions.

Metal-free oxidative cyclization of 2-aminobenzothiazoles and cyclic ketones enabled by the combination of elemental sulfur and oxygen


http://pubs.rsc.org/en/Content/ArticleLanding/2017/GC/C7GC02014G?utm_source=feedburner&utm_medium=feed&utm_campaign=Feed%3A+rss%2FGC+%28RSC+-+Green+Chem.+latest+articles%29#!divAbstract

Abstract

Metal-free oxidative cyclization for the one-pot synthesis of benzo[d]imidazo[2,1-b]thiazoles from 2-aminobenzothiazoles and cyclic ketones is described. Elemental sulfur combined with molecular oxygen as the benign co-oxidant was found to be unique and highly effective to promote this transformation without the aid of any metal salts. Various cyclic ketones smoothly reacted with 2-aminobenzothiazoles to give functional benzo[d]imidazo[2,1-b]thiazoles in good to very high yields, which thereby demonstrated the synthetic convergence of this methodology.
Graphical abstract: Metal-free oxidative cyclization of 2-aminobenzothiazoles and cyclic ketones enabled by the combination of elemental sulfur and oxygen
 
 
7,8,9,10-Tetrahydrobenzo[d]benzo[4,5]imidazo[2,1-b]thiazole (3a)
White solid; yield: 39.2 mg (86%), mp 140-142 °C.
STR1
 
1H NMR (400 MHz, CDCl3, ppm) δ 7.67-7.62 (m, 2H), 7.38 (t, J = 7.76 Hz, 1H), 7.27 (t, J = 7.68 Hz, 1H), 3.07-3.04 (m, 2H), 2.77-2.74 (m, 2H), 2.00-1.95 (m, 2H), 1.92-1.86 (m, 2H);
 
13C NMR (100 MHz, CDCl3, ppm) δ 145.1, 142.4, 132.9, 129.7, 125.5, 123.9, 123.5, 121.8, 111.9, 24.8, 22.8, 22.7, 21.8;
 
MS (EI) m/z (%) 228, 200 (100), 160, 108, 51;
 
HRMS calcd. for: C13H13N2S + (M+H)+ 229.07940, found 229.07941.
 
 
 STR2
 
 
str3
PREDICT
 
STR1
 
STR2
cas 325766-28-7
C13 H12 N2 S, 228.31,  Benzimidazo[2,​1-​b]​benzothiazole, 7,​8,​9,​10-​tetrahydro-
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C1CCCc2c1nc3sc4ccccc4n23