All the anhydrous solvents were redistilled over CaH2, or P2O5, or sodium/benzophenone prior to the reaction. (2S,3S,4R,5R)-3,4-Bis((tert-butyldimethylsilyl)oxy)-5-(6-chloro-9H-purin-9-yl)tetrahy- droselenophene-2-carbaldehyde (16a). To a solution of 15a [19] (348 mg, 0.60 ...