Process for preparing B-[(7a, 1713)-17-hydroxy-7-[9-[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]estra-1,3,5(10)-trien-3-yl]-boronic acid

1 . A process for the synthesis of B-[(7α,17β)-17-hydroxy-7-[9-[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]estra-1,3,5(10)-trien-3-yl]-boronic acid (ZB716), comprising the following steps:

a) reaction of intermediate N-3, (7α,17β)-7-[9-[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]-estra-1,3,5(10)-triene-3,17-diol (Fulvestrant), with a triflating agent to obtain intermediate N-2, (7α,17β)-7-[9-[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]-estra-1,3,5(10)-triene-3,17-diol-3-triflate:

b) reaction of intermediate N-2 with 4,4,4′,4′,5,5,5′,5′-octamethyl-2,2′-bi-1,3,2-dioxaborolane to obtain intermediate N-1, (7α,17β)-7-[9-[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]-3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-estra-1,3,5(10)-trien-17-ol:

c) treatment of intermediate N-1 to obtain compound ZB716, B-[(7α,17β)-17-hydroxy-7-[9-[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]estra-1,3,5(10)-trien-3-yl]-boronic acid:

2 . The process according to claim 1 , wherein in step a) an aromatic bis(trifluoromethanesulfonimide) of general formula Ar—N(Tf) 2 is used as triflating agent, wherein Ar indicates the aromatic or heterocyclic radical and the N(Tf) 2 group is the radical:

3 . The process according to claim 2 , wherein said triflating agent is 1,1,1-trifluoro-N-phenyl-N-[(trifluoromethyl)sulfonyl]methanesulfonamide.

4 . The process according to claim 1 , wherein the reagent used in step c) for the conversion of intermediate N-1 into compound ZB716 is an alkali metal periodate.

5 . The process according to claim 4 , wherein said reagent is sodium periodate.

6 . Compound (7α,17β)-7-[9-[(4,4,5,5,5-pentafluoropentyl)sulfinyl]nonyl]-estra-1,3,5(10)-triene-3,17-diol-3-triflate: