Design of C2-chiral diamines that are computationally predicted to be a million-fold more basic than the original proton sponges.
A set of C2-chiral diamines 18-21 based on 1,6-diazacyclodecane have been identified whose conjugate acids are predicted by B3LYP/6-31G calculations to have pKa values of approximately 23-6 on the water scale (pKa = 30-33 in MeCN); they are also expected to be kinetically active, but essentially nonnucleophilic. Strain relief on protonation largely determines the basicity of these compounds, and the key to the design of stronger bases is limiting conformational freedom, especially by preventing nitrogen inversion, through the introduction of additional ring fusions. 15,16-Dimethyl-15,16-diazatricyclo[9.3.1.1(4,8)]hexadecane (20) is examined in detail and shown to exist in 10 diastereomeric forms as a result of in-/out-isomerism. The predicted pKa values for these diastereomers range over 14 log units.
Alder
Roger W
RW
School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, United Kingdom. rog.alder@bris.ac.uk