A Simple Regioselective Demethylation of <i>p</i>‐Aryl Methyl Ethers Using Aluminum Chloride‐Dichloromethane System (2005)

Abstract Several aryl methyl ethers of phenolic esters and diaryl ketones have been selectively demethylated to their corresponding 4‐hydroxy derivatives by using aluminium chloride‐dichloromethane system at room temperature in good yields (53–85%). Keywords: Aryl methyl ethersregioselectivityaluminium chloride Acknowledgment The authors are grateful to the Director, CIMAP for providing facilities and encouragement for this work. The financial assistance from the Department of Science and Technology (DST), Govt. of India is duly acknowledged. Notes 1Selected data for 5a: 1H NMR (300 MHz CDCl3, TMS): 3.49 (s 3H C‐17, OCH3), 3.79 (s, 6H, 3′ & 5′, OCH3), 3.81 (s, 3H, C‐11, OCH3), 3.92 (s, 3H, 4′, OCH3). 13C NMR (75.46 MHz, CDCl3): 16.8 (C‐6), 24.2 (C‐14), 29.7 (C‐19), 32.3 (C‐15), 34.0 (C‐20), 49.0 (C‐21), 51.2 (C‐5), 51.6 (C‐16), 51.7 (OCH3 at C‐11), 53.7 (C‐3), 56.2 (3′ & 5′, OCH3), 60.80 (4′, OCH3), 77.8 (C‐18), 78.0 (C‐17), 95.3 (C‐12), 107.0 (C‐2′ & 6′), 108.0 (C‐7), 108.9 (C‐10), 118.9 (C‐9), 122.2 (C‐8), 125.3 (C‐1′), 130.5 (C‐2), 136.4 (C‐13), 143.0 (C‐4′), 152.9 (C‐3′ & 5′), 156.2 (C‐11), 165.4 (ester carbonyl at C‐18), 172.7 (ester carbonyl at C‐16); Electrospray Mass: 609 [M]+. Selected data for 5b: m.p.: oil. Yield: 68% 1H NMR (300 MHz, CDCl3, TMS): 3.52 (s, 3H, C‐17, OCH3), 3.84 (s, 9H, C‐11, 3′ & 5′, OCH3), 13C NMR (75.46 MHz, CDCl3): 51.87 (C‐17), 57.7 (3′ & 5′, OCH3), 60.7 (C‐11), 77.4 (C‐18), 79.6 (C‐17), 106.9 (C‐2′ & 6′), 124.9 (C‐1′), 138.4 (C‐4′), 153.9 (C‐3′ & 5′), 155.8 (C‐11), 171.6 (ester carbonyl at C‐16), 165.3 (ester carbonyl at C‐18). Electrospray Mass: 595 [M]+; Selected data for 6a: m.p.; 138–40°C; 1H NMR (300 MHz, CDCl3, TMS): 3.70 (s, 6H, 3′ & 5′, OCH3), 3.93 (s, 3H, 4′, OCH3), 6.90–7.93 (m, 8H, aromatic protons), 10.84 (s, 1H, phenolic OH); 13C NMR (75.46 MHz, CDCl3): 56.63 (3′ & 5′ OCH3), 61.02 (4′, OCH3), 108.57–160.47 (aromatic carbons), 198.73 (ketone); Electrospray Mass: 360.9 [M + Na]+, 338.9 [M + H]+; Analysis: C20H18O5, Calcd: C, 71.01%; H, 5.32%. Obsd: C, 71.48%; H, 4.92%. Selected data for 6b: Yield 69 mg (72%). m.p.: 116–18°C. 1H NMR (300 MHz, CDCl3, TMS): 3.75 (s, 6H, 3′ & 5′, OCH3), 6.96–7.94 (m, 8H, aromatic protons), 5.99 (s, 1H, phenolic OH), 10.92 (s, 1H, phenolic OH); 13C NMR (75.46 MHz, CDCl3): 56.33 (3′ & 5′, OCH3), 107.47–159.79 (aromatic carbons), 198.29 (ketone); Analysis: C19H16O5, Calcd: C, 67.28%; H, 4.94%. Obsd: C, 66.84%; H, 4.69%. Selected data for 7a: m.p.: 132–35°C; 1H NMR (300 MHz, CDCl3, TMS): 3.74 (s, 6H, 3′ & 5′, OCH3), 3.92 (s, 3H, 4′, OCH3), 4.77 (s, 2H, OCH2), 7.16–7.97 (m, 8H, aromatic); 13C NMR (75.46 MHz, CDCl3): 56.73 (3′ & 5′, OCH3), 60.86 (4′, OCH3), 67.17 (OCH2), 108.85–153.60 (aromatic carbons), 170.39 (‐COOH), 196.11 (ketone); Electrospray Mass: 419 [M + Na]+, 397 [M + H]+; Analysis: C22H20O7, Calcd: C, 66.67%; H, 5.05%. Obsd: C, 67.18%; H, 5.39%. Selected data for 7b: Yield: 53%. m.p.: 109–110°C. 1H NMR (300 MHz, CDCl3, TMS): 3.80 (s, 6H, 3′ & 5′, OCH3), (s, 2H, OCH2), 7.18–7.72 (m, 8H, aromatic protons); 13C NMR (75.46 MHz, CDCl3): 56.62 (3′ & 5′‐OCH3), 67.24 (OCH2), 109.1–154.42 (aromatic carbons), 170.68 (‐COOH), 196.62 (ketone); Analysis: C21H18O7, Calcd: C, 65.97%; H, 4.71%. Obsd: C, 66.43%; H, 4.29%.