Improved synthesis of the polyhydroxylated central part of phoslactomycin B

A new approach to the C(7)–C(13) intermediate for the synthesis of phoslactomycin B was investigated. Asymmetric dihydroxylation of the β,γ-unsaturated ester proceeded cleanly to afford the β-hydroxyl-γ-lactone with 97.6% ee, which upon protection as the PMB ether followed by hydride reduction furnished a diol. After selective protection of the prim-OH, oxidation of the sec-OH and chelation-controlled addition of CH2CHMgBr afforded the C(7)–C(11) segment. Later on, the C(11) stereocentre was constructed by the asymmetric transfer hydrogenation using the Noyori catalyst.