Asymmetric allylboration and ring closing alkene metathesis: A novel strategy for the synthesis of glycosphingolipids

A novel strategy for the synthesis of D,L-glucosylceramide 1, a member of the glycosphingolipid class of natural products is described. Reagent-controlled asymmetric Brown allylboration gave excellent stereochemical control in the construction of adjacent stereocenters in the sphingoid base portion of the molecule. The trans-configured double bond was obtained as a single geometrical isomer by use of silicon-tethered olefin metathesis employing the Schrock carbene [(CF3)(2)MeCO](2)Mo-(=CHCMe2Ph)(=NC6H3-2,6-i-Pr-2) and in situ PhLi-induced ring-opening of the intermediate 5,6-dihydro-2H-1,2-oxasiline followed by protodesilylation with TBAF in DMSO. The synthesis was completed by long chain amide formation and global deprotection.