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Synlett 2015; 26(15): 2145-2150
DOI: 10.1055/s-0035-1560069
DOI: 10.1055/s-0035-1560069
letter
Copper(II)-Catalyzed Oxidative Esterification of Substituted p-Cresols under Ligand- and Additive-Free Conditions
Further Information
Publication History
Received: 05 May 2015
Accepted after revision: 09 July 2015
Publication Date:
12 August 2015 (online)
Abstract
A facile, atom-economical, and efficient Cu(OAc)2-catalyzed oxidative esterification of substituted p-cresols was developed with ambient air as the terminal oxidant. This ligand- and additive-free esterification protocol allows an environmentally benign and reagent-economical access to benzyl esters.
Key words
copper catalysis - esterification - substituted p-cresols - ambient air - sustainable reactionSupporting Information
- Supporting information for this article is available online at http://dx.doi.org/10.1055/s-0035-1560069.
- Supporting Information
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References and Notes
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- 17 General Procedure for the Synthesis of 3a A mixture of substrate 1a (1.0 mmol), benzoic acid (2a, 1.0 mmol), and Cu(OAc)2 (10 mol%) in MeCN (4.0 mL) was stirred under ambient air at 75 °C for 13 h. The reaction mixture was concentrated in vacuo to give a residue, to which were added HCl (10 mL, 2%) and EtOAc (15 mL). The organic phase was separated, and the aqueous phase was further extracted with EtOAc (5 mL, twice). The combined organic layers were washed with sat. aq NaHCO3 (20 mL) and brine (20 mL). The EtOAc was dried over anhydrous Na2SO4 and concentrated in vacuo to give a residue, which was purified by column chromatography on silica gel (eluents: PE–EtOAc, 30:1) to provide the corresponding product 3a. Characterization for 3a Yellow solid, mp 60–63 °C, 0.20 g (79%). 1H NMR (400 MHz, CDCl3): δ = 2.26 (s, 6 H), 4.67 (br s, 1 H), 5.23 (s, 2 H), 7.08 (s, 2 H), 7.42 (t, J = 8.0 Hz, 2 H), 7.55 (t, J = 8.0 Hz, 1 H), 8.06 (d, J = 8.0 Hz, 2 H) ppm. 13C NMR (100 MHz, CDCl3): δ = 16.0 (2 C), 66.9, 123.2 (2 C), 128.4 (2 C), 128.5, 129.3 (2 C), 129.7 (2 C), 130.2, 133.0, 152.4, 166.7 ppm. HRMS (EI): m/z [M+] calcd for C16H16O3: 256.1099; found: 256.1100
For selective reviews on C–C bond formation via C–H activation, see:
For selective reviews on C–X bond formation via C–H activation, see:
C–O bond formation:
C–N bond formation:
C–B bond formation:
For efficient recycling of Cu(OAc)2 by ambient air or O2, see: