Studies on the lithiation, borylation, and 1,2‐metalate rearrangement of O‐cycloalkyl 2,4,6‐triisopropylbenzoates

Varinder Kumar Aggarwal*, Rory Mykura, Pradip Songara, Eugenia Luc, Jack Rogers, Ellie Stammers

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

Abstract

A broad range of acyclic primary and secondary 2,4,6‐triisopropylbenzoate (TIB) esters have been used in lithiation‐borylation reactions, but cyclic TIB esters have not. We have studied the use of cyclic TIB esters in lithiation‐borylation reactions and looked at the effect of ring size (3 → 6‐membered rings) on the three key steps of the lithiation–borylation protocol: deprotonation, borylation and 1,2‐metalate rearrangement. While all rings sizes could be deprotonated, the cyclohexyl case was impractically slow, and the cyclopentyl example underwent α‐elimination faster than deprotonation at −78 °C and so could not be used. Both cyclobutyl and cyclopropyl cases underwent rapid borylation, but only the cyclobutyl substrate underwent 1,2‐metalate rearrangement. Thus, the cyclobutyl TIB ester occupies a “Goldilocks zone,” being small enough for deprotonation and large enough to enable 1,2‐migration. The generality of the reaction was explored with a broad range of boronic esters.
Original languageEnglish
Number of pages7
JournalAngewandte Chemie - International Edition
Early online date2 Mar 2021
DOIs
Publication statusE-pub ahead of print - 2 Mar 2021

Keywords

  • Boronic Esters
  • C-C coupling
  • lithiated carbamates
  • carbocycles
  • cyclobutane

Cite this