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Synlett 2012; 23(11): 1678-1682
DOI: 10.1055/s-0031-1291164
DOI: 10.1055/s-0031-1291164
letter
Palladium-Catalyzed C–H Cyclization in Water: A Milder Route to 2-Arylbenzothiazoles
Further Information
Publication History
Received: 29 February 2012
Accepted after revision: 19 April 2012
Publication Date:
13 June 2012 (online)
![](https://www.thieme-connect.de/media/synlett/201211/lookinside/thumbnails/10.1055-s-0031-1291164-1.jpg)
Abstract
Water was successfully employed as a reaction medium in palladium-catalyzed C–H cyclization of thiobenzanilides. Reactions efficiently proceeded under considerably mild conditions such as 40 °C in water, providing a more practical, greener method for the synthesis of 2-arylbenzothiazoles. For some substrates, the addition of an amphiphilic surfactant greatly enhanced the process. The method represents a rare example of palladium-catalyzed C–H functionalization processes performed in water.
Supporting Information
- for this article is available online at http://www.thieme-connect.com/ejournals/toc/synlett. Included are experimental procedures and spectroscopic data.
- Supporting Information
-
References and Notes
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- 12 Representative Procedure for the Synthesis of 2-Arylbenzothiazoles (Table 2, Entry 5, Conditions B) Under an O2 atmosphere, a mixture of N-(4-nitrophenyl)-thiobenzamide (1e, 37.2 mg, 0.14 mmol), Pd2(dba)3 (7.4 mg, 0.0081 mmol), tris(2-methylphenyl)phosphine (9.6 mg, 0.32 mmol), Rb2CO3 (36.2 mg, 0.16 mmol), and Triton X-100 (29.7 mg, 0.048 mmol) in H2O (3 mL) was stirred for 24 h at 40 °C. The reaction mixture was diluted with sat. aq NH4Cl (5 mL) and extracted with CHCl3 (3 × 30 mL), and then the combined organic layer was dried over Na2SO4. The solvent was removed under a reduced pressure, and the residue was purified by SiO2 column chromatography (eluent; 1% EtOAc in hexane) to give 6-nitro-2-phenylbenzothiazole (2e, 28.3 mg, 77%). Recrystallization from EtOAc–hexane gave pale orange prisms, mp 191–192 °C. 1H NMR (400 MHz, CDCl3/TMS): δ = 7.50–7.56 (m, 3 H), 8.09–8.12 (m, 3 H), 8.34 (dd, 1 H, J = 9.0, 2.3 Hz), 8.81 (d, 1 H, J = 2.3 Hz) ppm. 13C{1H} NMR (100 MHz, CDCl3/TMS): δ = 118.1, 121.8, 123.2, 127.8, 129.2, 132.1, 132.6, 135.2, 144.8, 157.7, 173.6 ppm. LRMS (EI): m/z = 256 [M+]. HRMS: m/z calcd for C13H8N2O2S: 256.0307; found: 256.0287. IR (neat): 1518, 1333 cm–1
For reviews on the use of amphiphilic surfactants for organic synthesis, see:
For selected recent reviews on transition-metal-catalyzed C–H functionalization, see:
For other examples of C–S formation via transition-metal-catalyzed or -mediated C–H functionalization, see:
For selected recent reports on the use of amphiphilic surfactants in transition-metal-catalyzed processes, see:
Only a few examples of Pd-catalyzed C–H functionalization processes using water as a reaction medium have so far been reported, see:
Several processes involving Ru-catalyzed C–H functionalization in water have recently been reported, see: