Regio‐ and Stereoselective Chlorocyanation of Alkynes

Abstract

A variety of terminal and internal alkynes were converted regio- and stereoselectively into (Z)-3-chloroacrylonitriles by treatment with BCl in the presence of stoichiometric amounts of imidazolium thiocyanates. These products could be readily functionalized to provide useful building blocks, thus demonstrating the synthetic value of the method. Preliminary mechanistic studies suggest initial activation of the cationic thiocyanate by the Lewis acid, followed by electrophilic attack of the alkyne. The syn addition of a chloride to the vinyl cation intermediate and final elimination of the thiourea unit afford the desired chloroacrylonitriles.

Direct cyanation, hydrocyanation, dicyanation and cyanofunctionalization of alkynes

“…In both cases, only the Z isomer was formed, thus suggesting a syn-addition pathway for the reaction (Scheme 13). 32 The following mechanism for the chlorocyanation reaction was proposed. Initially, Lewis adduct H which was already partially uorinated at boron was formed by activation of the cyanating reagent 29.…”

5‐(Cyano)dibenzothiophenium Triflate: A Sulfur‐Based Reagent for Electrophilic Cyanation and Cyanocyclizations

“…[14] It was not until the introduction of cyanobenziodoxone 7 by Zhdankin and coworkers, [15] and its intensive use by the groups of Waser [16] and others [17] that metal-free electrophilic cyanationa tu nfunctionalized CÀHp ositions of electron-rich organic substrates could be efficiently achieved ( Figure 1). [18] Nature often uses carbocationic cascade cyclizations to produce complex molecular architectures from simple precursors,a nd chemists have been quite successful at transferring this strategy into routine synthesis planning. [18] Nature often uses carbocationic cascade cyclizations to produce complex molecular architectures from simple precursors,a nd chemists have been quite successful at transferring this strategy into routine synthesis planning.…”

“…We recently contributed to this area with the introduction of the imidazolium thiocyanate 8,which has areactivity profile similar to the one of 7,but is not based on thermally unstable hypervalent I(III) platforms. [18] Nature often uses carbocationic cascade cyclizations to produce complex molecular architectures from simple precursors,a nd chemists have been quite successful at transferring this strategy into routine synthesis planning. [19] Initiation of such cyclizations is often triggered by elimination of aleaving group,the activation of olefins by p-acid catalysts,or the reaction of carbon-carbon double bonds with electrophiles.…”

5‐(Alkynyl)dibenzothiophenium Triflates: Sulfur‐Based Reagents for Electrophilic Alkynylation

“…In an attempt to find and develop such new reagents,w e originally focused our attention on the thioimidazolone platform, which has been successfully used in our group to develop the electrophilic cyanation reagents 1 (Figure 1). [14] However,the reactivity of the alkynylation reagents based on thioimidazolones is limited, and when strong nucleophilic Grignard reagents are used, the competitive thioalkynylation occurs exclusively. [15] At that stage we wondered if adibenzothiophenium unit could be employed instead.…”