Part I. Palladium-catalyzed alkenylation and alkynylation of nucleosides in aqueous media. Part II. Palladium-catalyzed carbon-selenium bond formation for unsymmetrical diaryl selenides

A wide variety of applications of C-modified nucleosides have prompted the continued development of efficient synthetic methods for modification of nucleosides. To achieve this end, Pd-catalyzed reactions were performed in aqueous solvents for alkenylation and alkynylation of nucleosides. In addition to the environmental and economic benefits of aqueous solvents, the use of aqueous solvents can make it possible to perform a direct transformation without protection of hydroxyl groups, which is needed for transformations in organic solvents.;In Pd-catalyzed alkenylation of unprotected halonucleosides, reactions of 5-iodo-2'-deoxyuridine (5-IdU) with alkenes were successfully completed in aqueous solvent to give the 5-alkenylated deoxyuridines in good to excellent yields (64--82%). Alkenylation of 5-IdU in the absence of phosphine ligand was also achieved in yields comparable to that of the presence of phosphine ligand, which resulted from a crucial role of triethylamine in the reactions. 8-Bromo-2'-deoxyadenosine (8-BrdA) and 8-bromo-2'-guanosine (8-BrdG) did not undergo Pd-catalyzed alkenylation.;In Pd-catalyzed alkynylation, tri(2,4-dimethyl-5-sulfonatophenyl)phosphine provided a highly active catalyst for alkynylation of halonucleosides. With this sterically demanding arylphosphine ligand, reactions of 8-BrdA, 8-BrdG, or 5-IdU with alkynes were completed to generate the alkynylated products in good to excellent yields.;Diaryl selenide compounds have been of significant interest in the areas of biological and materials chemistry as well as organic synthesis. It was found that reactions of aryl halides and phenylselenolate anions proceeded under catalytic conditions to generate the unsymmetrical diaryl selenides. Reaction of aryl iodides with PhSeNa occurred to give the diaryl selenides in excellent yields. In the reaction of aryl iodides, the bidentate chelating ligand, 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene provided an active catalyst for C-Se bond formations. Aryl bromides reacted with phenylselenolate anion generated in situ by treatment of (PhSe)2 with NaBH 4 in N,N-dimethylformamide solvent to generate diaryl selenides in excellent yields. In the reactions of aryl bromides, 1-dicyclohexylphosphino-2-(di- tert-butylphosphinomethyl) ferrocene provided an active catalyst for C-Se bond-forming reactions. The newly developed Pd-catalyzed C-Se bond-forming method can provide an efficient synthetic route to unsymmetrical diaryl selenides.