From C,N- and N,N-chelated chloroboranes to substituted 1H-2,1-benzazaboroles and 1H-pyrrolo[1,2-c][1,3,2]diazaborolidines: a straightforward route to five-membered rings containing the B–N or N–B–N moiety

Abstract

A set of 1H-2,1-benzazaboroles as B–N analogues of 1H-indene and a set of 1H-pyrrolo[1,2-c][1,3,2]diazaborolidines as B–N analogues of 1H-pyrrolizine were prepared via nucleophilic addition of selected alkyl(aryl)lithiums (MeLi, tBuLi or PhLi) to, via N→B intramolecular interactions, the activated imino CN functionality in the structure of C,N- or N,N-chelated chloroboranes. All compounds were characterized by elemental analysis and ¹H, ¹¹B, ¹³C and ¹⁵N NMR spectroscopy, and molecular structures of isolated compounds were on several occasions established by means of single-crystal X-ray diffraction analysis. The presence of three adjacently bonded substituents and their systematic alternation on five-membered C₃BN (1H-2,1-benzazaboroles) or C₂BN₂ (1H-pyrrolo[1,2-c][1,3,2]diazaborolidines) rings allowed us to follow both the influence of the steric repulsion and limitations for the formation of respective annulated heterocyclic systems.