Enantioselective Synthesis of Carbocyclic Nucleosides via Asymmetric [3+2] Annulation of α-Purine-Substituted Acrylates with MBH Carbonates

An efficierit route to chiral carbocyclic nucleoside analogues containing a quaternary stereocenter and a C=C double bond has been establishectia a highly enantioselective [3 + 2] annulation of Morita-Baylis-Hillman (MBH) carbonates with a-purine-substituted acrylates. With 20 mol % '(S)-SITCP as the catalyst,. various chiral carbocydic nucleoside analogues, with a quaternary stereocenter and C=C.double bond were obtained in high yields (up to 92%) with good diastereoselectivities (up to 10:1 dr) and excellent enantioselectivities (up to 96% ee). Furthermore,the corresponding products were subjected to diverse transformations to afford interesting and potentially useful chiral carbocyclic nucleosides.