Configurational Stability and Stannylation of Dipole‐Stabilised Cyclic Tertiary Benzylic α‐Oxycarbanions, which Occurs with Retention or Inversion of Configuration Depending on R and X of R3SnX Used

2,4,6-Triisopropylbenzoates of 1-indanol and 1-tetralol (ee 98%) are deprotonated at –78 °C in hexane by sBuLi/TMEDA to give partly configurationally labile organolithium intermediates 5a and 5b, which are deuterated by MeOD with retention of configuration. These intermediates are stannylated by trimethyltin chloride with inversion as determined by lithiodestannylation followed by addition of MeOD to produce deuterated esters of low ee. Stannylation of (S)-5b with (–)-menthyldimethyltin bromide affords stannane 7 (de ≥ 95%) with inversion. The carbanion derived from (S)-1-indanyl N,N-diisopropylcarbamate (9) is configurationally stable. It reacts with trimethyltin chloride favouring inversion of configuration (ee up to 17%). Tributyltin chloride and tributyltin triflate yield stannanes 11b of opposite stereochemistry, the latter giving retention of configuration. Tributyltin bromide behaves similarly to the chloride, but the ee of the reaction product is only about 30%.