A mechanism for ring opening of amine 4 involving Li(THF)2 + ions and two amines as proton transfer agents was also calculated (Scheme 5; model "b") and again the SN2 step precedes the proton transfers along a chain. The free energy the barrier is reduced to 26.9 kcal/mol, 5.1 kcal/mol lower than that Scheme 5. Reaction mechanisms for isomerization of amine 4 into product 3a: (a) in THF. (b) In THF in the presence of Li + ions. TS: transition state.