Synthesis of the C16-C35 fragment of integramycin using olefin hydroesterification as a linchpin reaction

reaction: see text] The spiroketal unit of the HIV-integrase inhibitor integramycin has been prepared in an efficient and convergent manner. Key steps in this sequence include the use of ruthenium-mediated hydroesterification reactions of homoallylic alcohols and silyl ethers, and a C,O-dianionic addition into a lactone provides the spiroketal while minimizing protecting group manipulations.