Development of a fully P(V) platform for oligonucleotide synthesis (A) Reagent development, (B) Overcoming chemoselectivity challenges (C) Overcoming historical P(V) rate challenges. PFP, pentafluorophenol; TFA, trifluoroacetic acid; DCA, dichloroacetic acid; DBP, dibutylphosphate; [S], sulfurization; DDTT, 3-((Dimethylamino-methylidene)amino)-3H-1,2,4-dithiazole-3-thione; DCI, 4,5-dicyanoimidazole; DBU, 1,8-Diazabicyclo[5.4.0]undec-7-ene.