Studies on the Lithiation, Borylation, and 1,2‐Metalate Rearrangement of O‐Cycloalkyl 2,4,6‐Triisopropylbenzoates

Abstract

Ab road range of acyclic primary and secondary 2,4,6-triisopropylbenzoate( TIB) esters have been used in lithiation-borylation reactions,b ut cyclic TIB esters have not. We have studied the use of cyclic TIB esters in lithiationborylation reactions and looked at the effect of ring size (3-! 6-membered rings) on the three key steps of the lithiationborylation protocol:deprotonation, borylation and 1,2-metalate rearrangement. Although all rings sizes could be deprotonated, the cyclohexyl case was impractically slow,a nd the cyclopentyl example underwent a-elimination faster than deprotonation at À78 8 8Ca nd so could not be used. Both cyclobutyl and cyclopropyl cases underwent rapid borylation, but only the cyclobutyl substrate underwent 1,2-metalate rearrangement. Thus,t he 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 ab road range of boronic esters.

Site‐ and Stereoselective C(sp3)−H Borylation of Strained (Hetero)Cycloalkanols Enabled by Iridium Catalysis

“…Subsequent C( sp 3 )−H borylation of 68 provided 69 in 66 % yield with 94 % ee. In addition, the α‐borylated cyclobutanol 55 b underwent dual functionalization and afforded 71 [26] . This route provides a promising method to access diverse gem ‐disubstituted cyclobutanes.…”