Enantioselective difunctionalization of alkenes by a palladium-catalyzed Heck/borylation sequence.

Yuanqi Wu,Junliang Zhang,Yu Liu,Bing Xu,Zhan-Ming Zhang,Lizuo Wu

doi:10.1039/d1sc06229h

Abstract

A palladium catalyzed enantioselective Heck/borylation reaction of alkene-tethered aryl iodides was realized, delivering a variety of 2,3-dihydrobenzofuranyl boronic esters in high yield with excellent enantioselectivity. Asymmetric synthesis of chromane boronic ester, indane boronic ester and indoline boronic ester was also accomplished. The protocol offers an efficient access to the corresponding chiral benzocyclic boronic esters, which are notably important chemical motifs in synthetic transformations.

Highlights

Versatile transformations of carbon–boron (C–B) bonds have been recognized as an ideal platform for the preparation of value-added molecules.[1]
Much effort has been devoted to developing efficient methods for the construction of C–B bonds,[2] in which, transition-metal-catalyzed asymmetric carboboration of alkenes represents one of the most step- and atom-economic tools for facile access to enantioenriched borylated compounds.[3]
Over the past few years, asymmetric carboboration of alkenes has been elegantly achieved by using dual metal synergistic or single metal catalysis, such as Cu/Pd,4 Pd,5 Cu-6 or Ni7-catalysis (Scheme 1a)

Summary

Introduction

Versatile transformations of carbon–boron (C–B) bonds have been recognized as an ideal platform for the preparation of value-added molecules.[1]. Despite the breakthroughs in this process, its application in the construction of chiral boron-containing benzocycles is underdeveloped. Several issues make the protocol challenging: (1) a direct Miyaura-type borylation seems to have an edge;[14] (2) competitive side reactions such as the reductive Heck reaction and carboiodination should be avoided;13a,b (3) the transmetalation step may take place prior to the alkene insertion, which could alter the steric environment and affect the enantioselectivity. We report a highly enantioselective Pd-catalyzed tandem Heck/borylation sequence, conveniently accessing various chiral benzocyclic boronic esters in good yields (Scheme 1c)

Results and discussion

Conclusions

Conflicts of interest