Pd-catalyzed asymmetric addition reaction of various heteratom nucleophiles to alkoxyallene will be presented. The reaction showed complete regioselectivity towards branched product formation. Numerous heteroatom nucleophiles participate well in this reaction (including alcohols, phenols, N-heterocycles, indoles, and carboxylic acids) to generate the corresponding O,O- and N,O-acetals in a stereochemically well-defined manner. Furthermore, this unique reaction was evolved into a de novo strategy towards highly useful O- and N-glycosides. In this context, application of this strategy to the synthesis of challenging targets such as deoxyoligosaccharides and ring-modified nucleosides will also be introduced.