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DOI: 10.1055/s-2004-817766
A Simple and Regioselective Carbon-Oxygen Bond Cleavage Using Niobium(V)
Publication History
Publication Date:
25 March 2004 (online)
Abstract
A simple and convenient method for the differentiation of alkoxy groups on aromatic rings is described. Niobium(V) is found to possess a strong Lewis acid property to transform alkyl arylethers smoothly to the corresponding phenols in high yields. The excellent regioselectivity was also observed in dialkoxy benzene derivatives under mild conditions.
Key words
dealkylation - Friedel-Crafts acylation - niobium
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References
Other Lewis acid agents, such as TiCl4, AlCl3, TaCl5 and MoCl5 (1.1 equiv) with 1a under similar conditions (PhMe, reflux), were quite ineffective to be resulted in the recovery of 1a with >95% yield even after 5 h. In case of WCl6 (1.1 equiv, toluene, reflux, 9 h), 2a was obtained in only 18% yield together with 3 (18%) and 1a (60%). BBr3 with 1a (CH2Cl2 at -78 °C) was also subjected and gave 2a (90%) with 3 (9%). In other substrates, NbCl5 is found to be more selective reagent than BBr3 in C-O bond cleavage, unpublished results.
12Typical Experimental Procedure for the Synthesis of 2a (Table 1, Entry 1): To a mixture of 1a (30 mg, 0.1 mmol) and NbCl5 (31 mg, 0.11 mmol) under an argon atomosphere, dichloroethane (1.0 mL) was added and the suspension was stirred for 3.5 h under reflux condition. The reaction mixture was quenched by 10% aq K2CO3 (1.0 mL) and extracted with CH2Cl2 (5.0 mL × 3). The resulting organic layer was washed with brine and dried over Na2SO4, and subsequent flash column chromatography (hexane:EtOAc = 8:1) gave the desired product 2a as a white amorphous (29.6 mg, 0.1 mmol, 100%).