Synthesis of (±)-branched-chain azaisonucleosides via Michael addition of 5-nitro-2,2-pentamethylene-1,3-dioxane to methyl 2-bromoacrylate

Michael reaction of 2,2-pentamethylene-5-nitro-1,3-dioxane 1 with methyl 2-bromoacrylate, generated in situ from methyl 2,3-dibromopropanoate and triethylamine, afforded α-bromo-γ-nitroester 3, which was readily converted into various 5,5-bis(hydroxymethyl)pyrrolidine analogues of nucleosides.