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. Author manuscript; available in PMC: 2020 Dec 4.
Published in final edited form as: Nucleosides Nucleotides Nucleic Acids. 2019 Oct 9;39(1-3):204–224. doi: 10.1080/15257770.2019.1671594

Scheme 1.

Scheme 1.

Synthesis of pentafluoro phosphoryl ester 4. Reagents and conditions: (a) (i) iPrOH, cat. H2SO4, rt, 18 h; (ii) NaHCO3 90%; (b) POCl3, t-BuOMe, rt 2 h; (c) Et3N, t-BuOMe, DCM, 2 h, rt; (d) Et3N, DCM, 5 oC, to rt, 2 h, 25% (2 steps).