Synthesis of 1-pyrroline 1-oxides analogous to pseudouridine

Pseudouridine (ψ-uridine, Ψ) aza′-analogues with a 5,5-bis(hydroxymethyl)-1-pyrrolin-2-yl 1-oxide as the glycone mimic were obtained by the addition of (2,4-dimethoxypyrimidin-5-yl)magnesium bromide to 1-aza-7,14-dioxadispiro[4.2.5.2]pentadec-1-ene 1-oxide (3), followed by oxidation and removal of the protecting groups. The analogous synthesis from (2,4-dimethoxypyrimidin-5-yl)lithium and 3 was less efficient; in the first step of the reaction sequence, competing dimerisation of 3 predominated over addition of the organolithium agent to 3.