Organolithium Mechanism

November 12, 2011 by Admin No comments

Organolithium Mechanism

Organolithium Mechanism

Finally, two other experiments were performed to confirm the mechanisms of both organolithium and organotitanium. In the first experiment, (R)-8 was trapped with Ph3SnCl to give allene 9c, structure of which was confirmed by x-ray. Because previous study of stannylation of propargyllithium/2 system showed the mechanism to be anti-SE', thus this result showed that the configuration of 8 was R.

The kinetic organolithium (S)-8 was transmetalated with titanium to form (S)-10 which reacted with chiral aldehyde 12 to give 11b, the structure of which was confirmed by x-ray. Because it is known that chiral alpha-(carbamoyloxy)allyltitanium compounds react with chiral aldehydes with strict chirality transfer from the Zimmerman–Traxler transition state. Therefore, configuration shown in 11 must be generated from (S)-10, which in turn was obtained by inversion of configuration of (S)-8.

Reaction of 8 with other electrophiles were also reported as summarized in the table below.

Conclusion for the current system:

1) Organolithium ---> anti-SE' addition to give allenyl alcohols
2) Lithium-titanium exchange ---> inversion of configuration
3) Organotitanium ---> syn addition via Zimmerman-Traxler transition state to give homoallylic alcohol
4) Organolithium was generated stereoselectively with n-BuLi/(-)-sparteine system. This kinetic organolithium can epimerize to give the opposite configuration upon prolonged reaction time.


cost of lithium
lithium protons