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

摘要

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