Controlling Diaza-Cope Rearrangement Reactions with Resonance-Assisted Hydrogen Bonds

NMR studies reveal that the equilibrium between 1 and 2 lies essentially toward 1 to the left without any detectable amount of 2. DFT computation shows that the value of K1 is about 1.4 × 10-5, and X-ray crystal structures show that the resonance-assisted hydrogen bond (RAHB) in 1 (1.66 Å) is shorter than the regular hydrogen bond in 2 (1.75 Å). The enormous selectivity can be explained in terms of the strength of the RAHBs in 1 compared to that of the regular hydrogen bonds in 2.