Efficient <i>N</i>-Arylation and <i>N</i>-Alkenylation of the Five DNA/RNA Nucleobases

A general approach to N-arylation and N-alkenylation of all five DNA/RNA nucleobases at the nitrogen atom normally attached to the sugar moiety in DNA or RNA has been developed. Various protected or masked nucleobases engaged readily in the copper-mediated Chan−Lam−Evans-modified Ullmann condensation with a range of different boronic acids at room temperature and were subsequently converted to the corresponding deprotected or unmasked adducts. Different N3-protecting groups were examined in the case of thymine, where the benzoyl group afforded the highest yields. A 4-alkylthio-substituted pyrimidin-2(1H)-one served as both a cytosine and a uracil precursor and was N-arylated and N-alkenylated in high yields. Adenine was efficiently and selectively N-arylated and N-alkenylated at the N9 position by employing a bis-Boc-protected adenine derivative, while a bis-Boc-protected 2-amino-6-chloropurine served as guanine precursor and could also be selectively N9-arylated and N9-alkenylated.