Photoinduced Metal-Free Arylboration of Unactivated Alkenes: Synthesis of Indoline Boronic Ester

Abstract

The environmentally benign synthesis of indoline boronic esters, especially through a way of arylboration to alkenes, remains a challenge due to the use of transition metals or high temperature conditions. We describled a photoinduced metal-free arylboration of unactivated alkenes for the synthesis of indoline boronic esters and 1,2,3,4-tetrahydroquinoline boronic ester in good yields. This approach showed good compatibility and great efficiency for a range of allylphenylamines as well as alkylamine. Remarkably, this transformation also suggested that the base is not necessary for photosensitizer-free diboron reagent-mediated mild generation of aryl radical. Furthermore, compared to previously reported methods, this approach is mild and environmentally benign.

Synthesis of Unsymmetrical 3,3′-Dialkyloxindole Boronic Esters from 3-Alkylidene-2-oxindoles Enabled by Copper Catalysis

“…Nonetheless, to the best of our knowledge, (di)­alkyloxindoles containing a B–C­(sp 3 ) moiety have been studied much less . In this realm, the group of Vachhani and Eycken described a palladium-catalyzed intramolecular arylation/borylation of α-substituted N -(2-iodo)­aryl acrylamides to furnish 3,3′-disubstituted oxindole boronic esters via a C­(sp 2 )–C­(sp 3 ) bond followed by C­(sp 3 )–B bond formation, and later the group of Ge and Lu reported an enantioselective variant of this transformation (Scheme a). , Recently, Ji et al developed a protocol for intramolecular arylation/borylation of α-substituted N -(2-iodo)­aryl acrylamides to afford 3,3′-disubstituted oxindole boronic esters, enabled by Cu/Phen catalysis (Scheme a) .…”