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A variety of applications of C‐alkynylated nucleosides has prompted the continuing development of efficient synthetic methods for their preparation. We report an efficient andenvironmentally benign Sonogashira coupling reaction for alkynylation of unprotected halonucleosides in an aqueous solvent. The combination of Pd(OAc)2, CuI, and TXPTS [trisodium tri(2,4‐dimethyl‐5‐sulfonatophenyl)phosphane] provided an effective catalyst for the alkynylation of 8‐bromopurines and 5‐iodouridine in H2O/CH3CN (1:1) in yields ranging from 42 to 98 %.

In this unit, an efficient method for the synthesis of alkyne-modified nucleosides in an aqueous solvent system is described. The method allows direct palladium-catalyzed alkynylation of readily available unprotected 8-bromo-2'-deoxyguanosine (8-BrdG), 8-bromo-2'-deoxyadenosene (8-BrdA), 8-bromoadenosine (8-BrA), and 5-iodo-2'-deoxyuridine (5-IdU) precursors. The optimal catalyst is derived from palladium acetate, tri-(2,4-dimethyl-5-sulfonatophenyl)phosphane (TXPTS), and CuI.