On the Preparation and Determination of Configurational Stability of Chiral Thio- and Bromo[D₁]methyllithiums

Thio- and bromo­[D₁]­methyllithiums (ee 99%) were generated from the respective stannanes by tin–lithium exchange at temperatures ranging from 0 to −95 °C. Thio­[D₁]­methyllithiums <b>6</b> were found to be microscopically configurationally labile on the time scale of the thiophosphate-α-mercaptophosphonate rearrangement even at −95 °C. Thio­[D₁]­methyllithiums <b>13a</b> and <b>13b</b> underwent a thia-[2,3]-Wittig rearrangement down to −95 °C and <b>13b</b> only down to −50 °C. The former were microscopically configurationally stable below −95 °C, and the latter racemized completely at −50 °C. Chiral bromo­[D₁]­methyllithiums are chemically unstable at −78 °C but microscopically configurationally stable at the time scale of their addition to benzaldehyde and acetophenone