A Solid‐State, Solution, and Theoretical Structural Study of Kinetic and Thermodynamic Lithiated Derivatives of a Simple Diazomethane and Their Reactivities Towards Aryl Isothiocyanates

Abstract

Abstract (Trimethylsilyl)diazomethane ( 1‐H ) reacts with n BuLi in THF at elevated temperature to afford (previously reported) 1‐Li· 3 / 2 THF . However, reaction in hexane/TMEDA at low temperature affords instead the N ‐lithiate Me 3 SiCNNLi·TMEDA ( 9 ), which is a novel “open” pseudo‐cubic tetramer in the solid state. Variable‐temperature NMR spectroscopy suggests that N ‐metallated 9 , apparently the kinetic product of the reaction, irreversibly rearranges at high temperature in solution to give the thermodynamically preferred C ‐lithiated isomer. These observations, supported by DFT calculations, influence our understanding of the reactivity of lithiated diazomethanes towards aryl isothiocyanates, suggesting as they do that previously observed product selectivity in these reactions is critically dependent on temperature control exercised during the process. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)