Lewis Acid Catalyzed Addition of Pyrazoles to Alkynes: Selective Synthesis of Double and Single Addition Products

Abstract

Silver and zinc salts were found to efficiently catalyze the addition of an N-H bond of pyrazoles to alkynes. With silver triflate as a catalyst, two pyrazoles regioselectively attacked the same carbon atom of the CϵC bond of aliphatic terminal alkynes to give gem-dipyrazolylalkanes predominantly. Replacement of silver triflate with zinc triflate allows us to achieve double addition of pyrazoles to aromatic terminal alkynes. In contrast to the selective double addition, the corresponding single addition of aliphatic and aromatic terminal

Chemo-, Regio-, and Stereoselective N-Alkenylation of Pyrazoles/Benzpyrazoles Using Activated and Unactivated Alkynes

“…In past decades hydroamination reactions on aliphatic alkynes have been reported using expensive metal catalyst. , Therefore, we examined the developed strategy for aliphatic alkynes 2aa – ak bearing long chain, an alicyclic ring, hydroxyl, ether, and ester group were utilized for the synthesis of N -alkenylated pyrazoles 5a – m in 40–69% yields (Table ). The reaction with aliphatic alkyne 2aa and 2ab provided the ( Z )-vinylated products 5a – b in good yields (entries 1–2).…”

“…In 2008, Tsuchimoto and co-workers reported the silver and zinc-catalyzed addition of N–H of pyrazoles onto alkynes using high catalyst loading (Scheme , (ii)) . Recently, Bhattacharjee and fellow workers use ruthenium complexes [Ru­(dppe)­(PPh 3 )­(CH 3 CN) 2 Cl]­[BPh 4 ] and [Ru­(dppp) 2 (PPh 3 )­(CH 3 CN)­Cl]­[BPh 4 ] for the generation of E - and Z - isomer, respectively (Scheme , (iii)).…”

Styrylpyrazoles: Properties, Synthesis and Transformations

“…Tsuchimoto et al reported a similar single addition of the N-H bond of pyrazoles to phenylacetylene and prop-1-yn-1-ylbenzene in the presence of a silver catalyst (AgNO 3 or AgOTf) to produce a regioisomeric mixture of 1-substituted pyrazoles 22 and 23 (Scheme 2) [55]. Complete stereoselectivity was achieved, since only the (Z)-isomer of 1-styrylpyrazole was formed, indicating that anti-addition, via a concerted mechanism, in which pyrazole nitrogen attacks the alkyne from the side opposite to a coordinated Lewis acid (LA), is involved as a key step in the reaction process [55]. [53].…”

“…Addition of pyrazole 20 to alkynes to produce (Z)-1-styrylpyrazoles 21-23[54,55].The role of two ruthenium complexes [Ru(dppe)(PPh3)(CH3CN)2Cl][BPh4] (24) (dppe = diphenylphosphinoethane) and [Ru(dppp)2(NCCH3)Cl][BPh4] (25) (dppp = diphenylphosphinopropane) as efficient catalysts in the regio-and stereoselective addition of…”

Direct Access for the Regio- and Stereoselective Synthesis of N-Alkenylpyrazoles and Chromenopyrazoles

“…These compounds are prepared by addition of alkynes to pyrazoles. In 2008, Tsuchimoto et al reported the Lewis acid-catalyzed addition of pyrazoles with alkynes (Figure ). Das et al developed the Ru-catalyzed regio- and stereoselective vinylation of pyrazoles with alkynes (Figure , A) .…”