Nucleosides and nucleotides. 189. Investigation of the stereoselective coupling of thymine with meso-thiolane-3,4-diol-1-oxide derivatives via the Pummerer reaction
We investigated the stereoselective coupling of thymine with sulfoxides derived from meso-thiolane-3,4-diol via the Pummererreaction. The introduction of 2,4-dimethoxybenzoyl groups to the hydroxyl groups of meso-thiolane-3,4-diol-1-oxide was effective to afford (2R∗, 3R∗, 4S∗)-1-[3,4-di-O-(2,4-dimethoxybenzoyl)thiolane-3,4-diol-2-yl]thymine stereoselectively.
Spiro C-arylglycoriboside was synthesized in 21 steps via Pd(II)-catalyzed spirocyclization as a key reaction. Hemiketal was obtained in 47% overall yield from cis-2-butene-1,4-diol and spirocyclized with PdCl 2 (PhCN) 2 in dilute THF solution (0.01 M) to afford the 1,6-dioxaspiro[4.4]nonane skeleton in high yield. The spirocyclo adduct was transformed into spiro C-arylglycoriboside in five steps.
-hexenal and methanol gave substituted furanoside in moderate yield, exclusively via 5-exo-mode cyclization, without the need for a reoxidant. New stereogenic centers at C1 and C4 on the tetrahydrofuran ring showed preferential 1R and 4R stereochemistry due to anomeric effect (n o -σ * c-o ) and A 1,2 strain, respectively. This methodology was applied to stereocontrolled synthesis of pentoses: D-ribose