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

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. This journal is © the Partner Organisations 2014.