A peracetylated D-lactal (1,2-unsaturated lactose glycal), in which the C1-C2 bond of the reducing-end glucose is replaced by a double bond, and all six hydroxyls are acetate-protected. Glycals are versatile glycosylation building blocks and intermediates in carbohydrate synthesis, used in glycal-assembly oligosaccharide synthesis (Danishefsky-type), as electrophile precursors via epoxide or halogen activation, and as probes for glycosidases and glycosyltransferases.