水相钯(Ⅱ)催化羰基β位C(sp^3)—H芳基化反应

Palladium Catalyzed Arylation of C(sp^3)—H Bonds of Carbonyl β-position in Water

在水相中,以醋酸钯为催化剂,特戊酸银存在的条件下,首次实现了8-氨基喹啉导向的非活化羰基β位的C(sp^3)—H芳基化反应.该催化反应具有以水为溶剂、条件温和、催化体系简单、不需其它添加剂和惰性气体保护等优点,且反应具有良好的底物适应性和官能团容忍性,最高产率可达96%.该方法为在水相中发展其它类型的C—H官能团化反应研究起到参考作用.

The direct activation and functionalization of C-H bonds is fundamentally important in organic synthesis. Among different methods developed, transition metal-catalyzed intermolecular arylation of alkanes, which couples unactivated C（sp^3）-H bonds with aryl moieties, is recognized as one of the most powerful strategies to construct valuable arylated alkyl scaffolds. Tremendous progress has thus been made in this field, which usually require harsh reaction conditions such as high temperature and inert atmosphere as well as additives. Furthermore, the reaction media were usually organic solvents with undesirable toxicity and volatility, such as toluene, xylene, tert-amyl alcohol, dichloroethane, etc. Therefore, the development of efficient catalytic unactivated C（sp^3）-H arylation under mild reaction conditions is still highly demanded. Herein, we reported a general and practical palladium-catalyzed arylation of β-methylene C（sp^3）-H under aqueous conditions by the use of 8-aminoquinoline as directing groups. This method exhibited good to excellent yields up to 96% and good functional group tolerance without other additives and inert gas atmosphere. Meanwhile, the reaction showed good regioselectivity to the β-position of carbonyl group. Mechanism studies showed that the aliphatic Ag-carboxylate salt was critical for this reaction. The silver ion might weaken the C-I bond and function as halogen scavenger for the transformation, while pivalic acid ion might act as base during reaction. A representative procedure for this reaction is as following： To a 10 mL glass tube, N-（quinolin-8-yl）butyramide （42.8 mg, 0.2 mmol）, iodobenzene （67 μL, 0.4 mmol）, Pd（OAc）2 （4.5 mg）, AgPiv （83.6 mg, 0.4 mmol） in 0.4 mL H2O were stirred at 60℃ for 24 h, and then cooled to room temperature. The reaction mixture was extracted with EtOAc. The organic phase was washed with water, dried over magnesium sulfate, and concentrated. The crude product was purified with column chromatography （petroleurn/EtOAc） to provide the products in 61%-96% yields.