Synthesis of homo-C-nucleosides using pyrimidinylmethylenephosphoranes

Abstract

The direct synthesis of homo-C-nucleosides from pyrimidinylmethylenephosphoranes and protected D-ribose is described. Reaction of 2,3-O-isopropylidene-5-O-trityl-D-ribose (9) with pyrimidinylmethylenephosphoranes (5)–(8) gave protected α- and β-homo-C-nucleosides (14)–(21) and pyrimidinylolefins (10)–(13) in good yields. The ratio of α- and β-nucleosides depended on the properties of phosphoranes. Treatment of compounds (10)–(13) with base such as triethylamine or 1,8-diazabicyclo-[5.4.0] undec-7-ene (DBU) gave ring-closed products (14)–(21) in quantitative yields. Deprotection of compounds (14)–(21) with hydrochloric acid in either dioxan–water or methanol gave homo-C-nucleosides (22)–(32).