Copper‐Catalyzed Regioselective Formal Allylboration of Aryl‐Substituted Terminal Alkynes with Bis(pinacolato)diboron and Allyl Halides/Sulfonates

Abstract

A copper‐catalyzed formal allylboration of terminal alkynes using allyl bromides or sulfonates as electrophiles has been achieved. This method exhibits good regio‐/stereoselectivity and good functional‐group tolerance for various substituents on the aromatic rings of arylethynes. Through this strategy, various trisubstituted vinyl pinacol boronic esters with a 1,4‐diene skeleton have been constructed. In order to demonstrate the utility of this method, the resulting 1,4‐dienes with boron substitution were further used in transformations such as Suzuki coupling, oxidation, halogenation, and so on, leading to various important compounds.

Copper-Catalyzed Borylative Difunctionalization of π-Systems

“…Generally, excellent selectivity for the S N 2′ pathway was observed; however, the selectivity could be reversed in some cases, exemplified by 95a with 98:2 selectivity for the S N 2 pathway. A similar process was also reported by Zhao and Wang using allyl bromides …”

“…A similar process was also reported by Zhao and Wang using allyl bromides. 83 Recently, the Fanãnaś-Mastral group utilized 1,4-dibromo-2butene as an allylating reagent. 84 Interestingly, the reaction leaves a bromide handle intact, giving orthogonal functional groups for downstream functionalization.…”

Catalytic Alkyne Allylboration: A Quest for Selectivity

“…Copper/phosphine catalysis was also extended to the allylboration of alkynes with allyl (pseudo)­halides. The group of Wang reported that the use of CuBr and P­( n -Bu) 3 as catalyst can promote the three-component reaction to afford skipped dienyl boronates in good yield . However, the reaction is limited to terminal aryl alkynes, and variable mixtures of α- and γ-allylation isomers are obtained when 1,3-disubstituted allyl (pseudo)­halides are used (Scheme ).…”

Chemoselective Coupling of π‐Systems to Access Metallated 1,4‐ or 1,5‐Skipped Dienes in Multicomponent Reactions

“…In 2017, Zhao and Wang extended the scope of coppercatalyzed allylboration to terminal alkynes by employing allyl halides (Br or Cl) and sulfonates as electrophiles (Scheme 5-ii). [15] However, the reaction was limited to aryl alkynes and unsubstituted allyl electrophiles (cf. 16 c and 17 a).…”