Solvent‐directed Regioselective Benzylation of Adenine: Characterization of N9‐benzyladenine and N3‐benzyladenine

The preferred sites for the benzylation of adenine under basic conditions were proven to be the N9 and N3 positions. Formation of the N9‐benzyladenine product is favored in polar aprotic solvents, such as DMSO, whereas the proportion of N3‐benzyladenine formed increases as the proportion of polar protic solvents, such as water, increases. X‐ray crystal structures were obtained for both N9‐benzyladenine and N3‐benzyladenine. ¹H‐¹³C HMBC NMR spectroscopy revealed diagnostic correlations used to assign the ¹H and ¹³C NMR chemical shifts confirming that the solution structures in three different solvents were the same as the isolated crystals. ¹³C NMR assignment for N9‐benzyladenine, N3‐benzyladenine, and N7‐benzyladenine was confirmed by computation using ADF.