text: The synthesis of the D ring (scheme 6) started from 44 with allylic bromination with copper(I) bromide and benzoyl tert-butyl peroxide to bromide 45. By adding even more bromide, another bromide 46 formed (both compounds are in chemical equilibrium) with the bromine atom in an axial position. Osmium tetroxide added two hydroxyl groups to the exocyclic double bond in diol 47 and oxetane ring-closure to 48 took place with DBU in a nucleophilic substitution. Then, acylation of the C4 hydroxyl group (acetic anhydride, DMAP, pyridine) resulted in acetate 49. In the final steps phenyllithium opened the ester group to form hydroxy carbonate 50,  both TES groups were removed (HF, pyr) to triol 51 (baccatin III) and the C7 hydroxyl group was back-protected to 52.