On the Configurational Stability of Chiral, Nonracemic Fluoro‐ and Iodo‐[D 1 ]Methyllithiums

Enantiomerically pure fluoro‐[D 1 ]methyllithium and iodo‐[D 1 ]methyllithiums of up to 92 %  ee were generated by transmetalation of the corresponding stannanes with MeLi in THF at various temperatures. The intermediate halo‐[D 1 ]methyllithiums were trapped with benzaldehyde or acetophenone already present in excess in the reaction mixture to either give halohydrins or to disintegrate to carbene. The fluoro‐[D 1 ]methyllithiums were found to be microscopically configurationally stable within the tested range of −95 to 0 °C, but chemically only stable at temperatures below −95 °C due to a rapidly increasing portion disintegrating to carbene. The iodo‐[D 1 ]methyllithiums were configurationally labile relative to the rate of addition to PhCHO at all temperatures tested (−95 to −30 °C). Disintegration to carbene interfered as well.