Retrosynthetic Analysis 2 12 PP Br Br Alkylate 14 Johnson orthoester claisen rearrangment Eto o EtoO Carbonyl addition CHO Brig 19 18Retrosynthetic Analysis 2 O O O O PPh3 9 O O O O Br 11 O Br Alkylation O Br Br + 12 13 14 O 10 15 EtO O Johnson orthoester claisen rearangment EtO O 16 HO 17 BrMg 18 CHO 19 + Carbonyl addition