The DFT model was expanded to consider chemoselectivity (see SI, Figure ). To simplify the possible reaction outcomes the substrate was modified to avoid the complication of facial selectivity. Calculations suggest that the syn-addition of a two equiv. of the diphenyl substituted cyclopropene 2c to 1b to form the double insertion product 4c is energetically feasible. The first insertion occurs with a barrier of G ‡ (298K) = 6.6 kcal mol -1 , the second with a barrier of G ‡ (298K) = 15.8 kcal mol -1 , the overall reaction is exergonic by G°(298K) = -80.5 kcal mol -1 . Hence, while the barrier to the second syn-insertion is marginally higher than the first, both are expected to be accessible under the experimental conditions. Isolation of 3b•(THF)2 -a organomagnesium compounds with a defined stereochemistry -provides an opportunity to investigate the stereointegrity of centres adjacent to the magnesium site. The stereoselective formation of organomagnesium compounds is a continued topic of interest and there are open questions about the rates and mechanisms of epimerisation. 3b is formed under kinetic control due to the syn-addition pathway described above. The anti-isomer is expected to be thermodynamically more stable based on steric grounds. Monitoring 13.8 mM concentration solutions of 3b• (THF)2 in C6D6 solution over 120 h at 25 °C and then 120 h at 60 °C provided no evidence for epimerisation. The data suggest that 3b retains a syn-stereochemistry up to modest temperatures and that epimerisation in this system is not facile.