Large-Scale Synthesis of Eldecalcitol

Industrial-scale synthesis of eldecalcitol is described. AA highly diastereoselective epoxidation of p-methoxybenzyl (PMB) protected dienol at room temperature provides the key epoxide intermediate with a secondary hydroxyl group, which is alkylated with a triflate to set up all of the subunits at the C-1, C-2, and C-3 positions of the A-ring fragment. Selective protecting group manipulation followed by palladium-catalyzed cyclization then provides the A-ring synthon. The C/D-ring fragment is obtained by (1) direct C-H hydroxylation of Grundman’s ketone using in situ prepared trifluoropropanone dioxirane and (2) protection. Finally, the coupling of the A-ring with the C/D-ring fragment, global deprotection, and recrystallization provide the highly crystalline eldecalcitol.