We also checked the stability of amine 4 in other solvents. In acetonitrile, dimethylsulfoxide, and chloroform it was stable even under prolonged heating (entries 6-11). However, in methanol, the isomerization already took place even under room temperature (entries 12, 13). Under heating, it was much faster (entry 14). This experiment explained why we never observed amine 4 in the reduction of nitrile 3 with NaBH4, CoCl2 (cat.) in methanol under reflux: the initially formed amine 4 isomerized into product 3a in methanol. DFT-calculations were performed to rationalize the observed results. A mechanism for ring opening of amine 4 involving only three additional amines (as methylamine) in the proton transfer process is shown in Scheme 5 (model "a"). It is a stepwise reaction in which the first stage involves an intramolecular SN2 mechanism (TS-1) followed by a cascade of much lower energy proton transfers in a chain (TS-2, TS-3) to form the exoenergic product 3a. The calculated free energy barrier for the ratelimiting SN2 step was 32.9 kcal/mol at the ωB97XD/Def2-SVPP and 32.0 at the ωB97XD/Def2-TZVPP levels (THF continuum solvent model applied), indicating only a small basis set dependence.