New zwitterionic heterocycles derived from 1-chloro(dimethyl)silyl-1-borylalkenes and 2-lithio-1-methylimidazole and 1-lithio-indazole

The 1-alkynyl(chloro)dimethylsilane 'BuC=CSiMe2Cl(1) reacts with tetraethyl -diborane(6) or 9-borabicyclo[3.3.1]nonane dimer, (9-BBN)(2), to give the ( Z)-1-chloro-dimethylsily1-1-diethylboryl-alkenes 2 and 3. These alkenes rea ct with 2-lithio-1-methylimidazole or 1-lithio-indazole by formation of LiC l and of 4, 5 and 9 together with small amounts of 6, 7 or 8 as minor produ cts. In 9 and 5, a zwitterionic structure is present which can be alternati vely described as a borane adduct of a carbene. All new compounds were char acterised by H-1-, B-11-, C-13-, N-15- and Si-29-NMR spectroscopy, and the molecular structure of 5 was determined by X-ray structural analysis. (C) 2 000 Elsevier Science S.A. All rights reserved.