Carbon Atom Deletion Strategy Enabled Synthesis of 22- <i>epi</i> -6-Deoxocastasterone Using the Intact Skeleton of Tigogenin

A stepwise carbon atom deletion strategy was developed to construct the brassinosteroid-type side chain from intact steroidal sapogenins with high atom economy. Key C23 deletion via oxidation, Favorskii rearrangement, and decarboxylative borylation converted the inherent C25 chiral methyl into the target C24 methyl. Further transformations, including spiroketal ring-opening and one-pot Barton-McCombie deoxygenation, enabled the efficient synthesis of a non-natural analogue, 22-<i>epi</i>-6-deoxocastasterone, offering a novel route for structural diversification.