Metal‐Free and syn‐Selective Hydrohalogenation of Alkynes through a Pseudo‐Intramolecular Process

Abstract

Dedicated to Ryoma on the occasion of his birthday.A new metal-free hydrohalogenation method for alkynes has been developed, which proceeds through a pseudo-intramolecular process. In this reaction, ethynylaniline serves as a substrate to quantitatively form an anilinium salt upon treatment with hydrochloric acid. The spatial proximity facilitates the efficient electrophilic addition of HCl to the ethynyl group in syn-mode, affording the corresponding chloroalkene without overaddition. This protocol was applied to HBr and HI, and the corresponding bromo-and iodoalkenes were obtained, respectively. The obtained chloroalkene was converted to tri-substituted alkenes possessing different aryl/alkynyl groups through Pd-catalyzed cross-coupling reactions.

An Unexpended Stereocontrolled Rearrangement of Ethyl 4‐Hydroxy‐4‐(substituted phenyl)‐2‐butynoate to Tetrasubstituted Alkenes with MeSOCl2

“…General Synthesis Procedure for compounds (9,11,13,15) To a solution of alkynoate derivatives (0.52 mmol, 1 equiv.) (8,10,12,14) in DCM (10 mL) was, added MsCl (1.04 mmol, 2 equiv.) and NEt 3 (1.04 mmol, 2 equiv.)…”

“…These studies are limited as it is applicable only to terminal acetylenes. Nishiwaki and coworkers developed a new metal‐free hydrohalogenation method through a pseudo‐intramolecular process but in that reaction, only ethynyl aniline derivatives were used as starting compounds (Scheme 1c) [12] . The use of HCl as a reagent inherently limits the functional‐group tolerance of these methods.…”

A new approach to 10-arylated 5H-dibenzo[b,f]azepines using syn-selective hydrohalogenation of ethynylaniline

“…We previously demonstrated an effective hydrohalogenation method that used 2-ethynylaniline as a substrate and involved a pseudo-intramolecular process. 6 The salt formation between an amino group and an acidic reagent was a crucial step to increase the proximity between the reactants, and this facilitated hydrochlorination even in the absence of a metal catalyst or special reagent, without the formation of any detectable overaddition products (Fig. 1).…”

Chemodivergent Sulfonylation of Enynones via Ionic and Radical Addition Modes of Sulfinic Acids

“…Plausible reaction mechanisms based on our control experiments are presented in Scheme for the chemodivergent addition of sulfonyl to enynones. The hydrosulfonylation to an alkyne moiety of enynones proceeds via an ionic addition pathway through a salt-controlled syn -addition fashion . The fact that the alkyne moiety is more electron-rich than the alkene moiety in the current enynone system can be a reason for the preferential hydrosulfonylation to the alkyne moiety.…”