By Huanfeng Jiang, Chuanle Zhu, Wanqing Wu
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Extra info for Haloalkyne Chemistry
Initially, the bromoalkyne intermediate was formed through the Ag-promoted bromination of terminal alkynes. 36 Proposed mechanism R1 H F Br R1 + AgOH Ag2O AgL F AgL Br R1 I R1 H R1 AgL + H I m H2O 35 Ag (Ag ) H2O Br AgF R1 R1 Br AgL 34 R1 Br Br AgL AgL 33 transferred to the corresponding vinylsilver intermediate 35 by trans-addition of AgF to bromoalkyne. Finally, protonation of 35 afforded the ﬁnal product and silver oxide. The high regio- and stereoselectivities were proposed to be originated from the back-side attack of the fluoride anion (34 to 35) as well as the bromide atom was regarded as both an activating and regio-directing functional group.
One of the most effective methods to access these compounds is the hydrothiolation of haloalkynes. In 2014, Zhu’s group documented a K2CO3-promoted hydrothiolation reaction of haloalkynes, producing β-halo alkenyl sulﬁdes in high yields with excellent regio- and stereoselectivities. 45) . 5 mmol). After stirring at room temperature for 10 h, the reaction mixture was quenched with water, extracted with EtOAc, dried over Na2SO4 and concentrated. Column chromatography on silica gel gave the βhalo alkenyl sulﬁde products.
Notably, this reaction was highly chemoselective, and the key to obtain satisfactory yields was the slow addition of the Grignard reagents to the reaction mixture. 20). 20 Copper-catalyzed cross-coupling of Grignard reagents with haloalkynes 28 3 Reactions of Haloalkynes General Procedure for Copper-Catalyzed Cross-Coupling of Grignard Reagents with Haloalkynes: A dry and nitrogen flushed four-necked flask (100 mL) equipped with a mechanical stirrer, a thermometer, a nitrogen inlet, and a septum was charged with CuCl2 (3 mol%), N-methylpyrrolidinone (4 mol%), haloalkyne (10 mmol), and THF (9 mL).