An Efficient Ga(OTf)₃/Isopropanol Catalytic System for Direct Reduction of Benzylic Alcohols

Abstract

This study aims to report the first gallium-catalyzed direct reduction of benzylic alcohols using isopropanol as a reductant. The reaction proceeds via gallium catalyst-assisted hydride transfer of the in situ-generated benzylic isopropyl ether. The method generates only water and acetone as byproducts and thus provides an atom-economic and environmentally friendly approach to the synthesis of di-and triarylmethanes, which are important substructures in various bioactive compounds and functional materials.

Formation and Disproportionation of Xanthenols to Xanthenes and Xanthones and Their Use in Synthesis

“…Yellow solid; yield 77.3% (1.6 g); mp: 60−63 °C; 1 H NMR (400 MHz, CDCl 3 ): δ 10.56 (d, J = 1.8 Hz, 1H), 8.22 (dd, J = 4.2, 2.2 Hz, 1H), 7.71 (dd, J = 8.7, 2.3 Hz, 1H), 7.49 (ddd, J = 10.9, 5.7, 2.1 Hz, 2H), 7.32 (td, J = 7.4, 1.4 Hz, 1H), 7.17−7.11 (m, 2H), 6.94−6.81 (m, 1H); 13 2-(4-Isopropylphenoxy)-5-methoxybenzaldehyde (17a). Yellow oil; yield 11.1% (240 mg); 1 H NMR (400 MHz, CDCl 3 ): δ 10.41 (s, 1H), 7.39 (d, J = 3.2 Hz, 1H), 7.23−7.16 (m, 2H), 7.11 (dd, J = 9.0, 3.2 Hz, 1H), 6.95−6.89 (m, 3H), 3.84 (s, 3H), 2.90 (p, J = 6.9 Hz, 1H), 1.25 (d, J = 6.9 Hz, 6H); 13 General Procedure for the Synthesis of Xanthenes and Xanthones. To a solution of the corresponding substrate a (1.0 mmol, 1 equiv.)…”

“…9H-xanthene (1b). 13 White solid; yield 42.0% (72 mg); mp: 99− 101 °C; 1 H NMR (400 MHz, CDCl 3 ): δ 7.25−7.14 (m, 4H), 7.09− 7.00 (m, 4H), 4.07 (s, 2H); 13 9H-Xanthen-9-one (1c). 7 White solid; yield 45.4% (89 mg); mp: 172−174 °C; 1 H NMR (400 MHz, CDCl 3 ): δ 8.35 (dd, J = 8.0, 1.4 Hz, 2H), 7.73 (td, J = 7.9, 7.2, 1.6 Hz, 2H), 7.50 (d, J = 8.5 Hz, 2H), 7.39 (t, J = 7.5 Hz, 2H); 13 4-Phenyl-9H-xanthene (7b).…”

“…13 White solid; yield 42.0% (72 mg); mp: 99− 101 °C; 1 H NMR (400 MHz, CDCl 3 ): δ 7.25−7.14 (m, 4H), 7.09− 7.00 (m, 4H), 4.07 (s, 2H); 13 9H-Xanthen-9-one (1c). 7 White solid; yield 45.4% (89 mg); mp: 172−174 °C; 1 H NMR (400 MHz, CDCl 3 ): δ 8.35 (dd, J = 8.0, 1.4 Hz, 2H), 7.73 (td, J = 7.9, 7.2, 1.6 Hz, 2H), 7.50 (d, J = 8.5 Hz, 2H), 7.39 (t, J = 7.5 Hz, 2H); 13 4-Phenyl-9H-xanthene (7b). 17 Yellow oil; yield 46.5% (120 mg); 1 H NMR (500 MHz, CDCl 3 ): δ 7.64 (d, J = 7.1 Hz, 2H), 7.49 (t, J = 7.6 Hz, 2H), 7.40 (t, J = 7.4 Hz, 1H), 7.28 (d, J = 6.1 Hz, 1H), 7.19 (q, J = 7.9 Hz, 3H), 7.12 (t, J = 7.5 Hz, 1H), 7.05 (t, J = 7.4 Hz, 1H), 6.99 (d, J = 8.1 Hz, 1H), 4.12 (s, 2H); 13 2-Trifluoromethoxy-9H-xanthen-9-one (13c).…”

“…7 White solid; yield 45.4% (89 mg); mp: 172−174 °C; 1 H NMR (400 MHz, CDCl 3 ): δ 8.35 (dd, J = 8.0, 1.4 Hz, 2H), 7.73 (td, J = 7.9, 7.2, 1.6 Hz, 2H), 7.50 (d, J = 8.5 Hz, 2H), 7.39 (t, J = 7.5 Hz, 2H); 13 4-Phenyl-9H-xanthene (7b). 17 Yellow oil; yield 46.5% (120 mg); 1 H NMR (500 MHz, CDCl 3 ): δ 7.64 (d, J = 7.1 Hz, 2H), 7.49 (t, J = 7.6 Hz, 2H), 7.40 (t, J = 7.4 Hz, 1H), 7.28 (d, J = 6.1 Hz, 1H), 7.19 (q, J = 7.9 Hz, 3H), 7.12 (t, J = 7.5 Hz, 1H), 7.05 (t, J = 7.4 Hz, 1H), 6.99 (d, J = 8.1 Hz, 1H), 4.12 (s, 2H); 13 2-Trifluoromethoxy-9H-xanthen-9-one (13c). 19 White solid; yield 24.6% (69 mg); mp: 170−172 °C; 1 H NMR (400 MHz, CDCl 3 ): δ 8.34 (dd, J = 8.0, 1.4 Hz, 1H), 8.19 (dt, J = 2.5, 0.9 Hz, 1H), 7.83− 7.70 (m, 1H), 7.63−7.48 (m, 3H), 7.45−7.38 (m, 1H); 13 9H-xanthene-2-carbonitrile (14b).…”

Direct deoxygenation of active allylic alcohols via metal-free catalysis

“…58–60 Continuing our research on the transformation of alcohols using specific acidic materials, 61–64 we believe that Brønsted acids can provide protons to activate the hydroxyl group of highly active allylic alcohols in order to break the C–O bond and generate carbocations. Meanwhile, benzyl alcohol can provide the hydrogen source that acts as the reductant for a series of reactions, 65–68 except hydrosilanes, hydrazine, Hantzsch ester, HCOOH, H 3 PO 3 , and so on. 69–71 Therefore, a simple and metal-free catalytic system containing only TsOH·H 2 O ( p -toluene sulfonic acid monohydrate) has been developed for direct deoxygenation of highly active allylic alcohols with p -methylbenzyl alcohol as the reducing agent, providing up to 94% yield of the product (Scheme 1(c)).…”