Regioselective Hydroiodination of Alkynes by in situ‐Generated HI

Abstract

An efficient and highly selective hydroiodination of alkynes has been reported. The reaction utilizes in situgenerated HI from [Rh]-complex, molecular hydrogen, and iodine under ambient temperature. The methodology provided the Markovnikov products exclusively from terminal alkynes, and predominately E-isomers from the internal alkynes in good yields. The reaction could be performed on a gram-scale with good yield.

Regio- and Stereoselective Hydroiodination of Internal Alkynes with Ex Situ-Generated HI

“…Furthermore, some hydroiodination reactions of internal alkynes display low stereoselectivity, which limits their application. ,, Recently, Oestreich et al reported the transition-metal-free hydroiodination of terminal and internal alkynes for the preparation of vinyl iodides using a HI surrogate, which was prepared from benzoic acid in several steps . In addition, Fan et al developed a Rh-catalyzed hydroiodination of terminal and internal alkynes under high H 2 pressure . However, the development of a practical and mild method for the regio- and stereoselective preparation of vinyl iodides by the hydroiodination of internal alkynes is still highly desirable.…”

“…The proposed mechanism is shown in Scheme , whereby the substrate alkyne is protonated by the strong acid HI to afford intermediate vinyl cation A . , The DFT geometry optimization of A indicates that it has a linear geometry, with its down face being sterically hindered by the phenyl group . Therefore, the attack of the iodide is favored from the upper side, giving the syn -addition product …”

Recent Progress in Haloalkene Synthesis by Hydrohalogenation (HX=HCl, HBr, HI) of Alkynes

“…Although conventional HI generation was performed Me 3 SiCl/NaI/H 2 O system reported by Ishii, [26] the reaction scope was narrow. In the past decade, several kinds of an in‐situ generation of HI have been well developed, For example, I 2 /PPh 3 /H 2 O system by Ogawa in 2014 (Scheme 5b), [27] I 2 /H 3 PO 3 system by Han in 2019 (Scheme 5c), [28] and rhodium catalyzed reduction of I 2 by Fan and Chen in 2020 were reported (Scheme 5d), [29] and all method show a broad substrate scope. In addition, Nozawa‐Kumada and Kondo reported ex‐situ generation of HI , in which a hydroiodination of internal alkynes were mainly studied (Scheme 5e) [30] …”

Ruthenium-Catalyzed Regioselective Hydrohalogenation of Alkynes Mediated by Trimethylsilyl Triflate

“…Then Corma’s group reported that Au(0) atoms in supported gold nanoparticles adsorbed and dissociated HCl in anhydrous organic solvents to give H–Au–(Au) n –Au–Cl transient species that reacted regio- and stereoselectively with alkynes adsorbed on the surface, leading catalytically to ( E )-vinyl chlorides (Scheme c) . Later, Fan and co-workers developed a selective hydroiodination of alkynes via a catalytic system based on [Rh]/I 2 /H 2 , which provided the Markovnikov products exclusively from terminal alkynes and predominately the E isomers from internal alkynes (Scheme d) . More recently, Morandi et al.…”

“…18 Later, Fan and co-workers developed a selective hydroiodination of alkynes via a catalytic system based on [Rh]/I 2 /H 2 , which provided the Markovnikov products exclusively from terminal alkynes and predominately the E isomers from internal alkynes (Scheme 1d). 19 More recently, Morandi et al demonstrated the synthesis of vinyl halides via a shuttle-catalysis-based Ir(I)catalyzed transfer hydrohalogenation of unactivated alkynes, which utilized chlorobutan-2-one as an HCl surrogate, enabling this protocol to tolerate a broad range of functional groups (Scheme 1e). 20 Although the above methods show many advantages, some of them meet limitations in special aspects such as operation under acidic or harsh conditions, narrow scope or a sole reactant, or easy occurrence of side reactions.…”