The reaction of ortho-lithiated triphenylmethyl benzyl ether with perbenzylated D-gluconolactone 1 followed by cyclization by BF3.Et2O provides a new stereospecific synthesis of C-glycosidic spiroketals. The structure of the peracetylated derivative was determined by X-ray diffraction. This methodology is applied to the synthesis of the spiroketal unit of papulacandins.