Reciprocal Donor Acceptor Selectivity (RDAS) and Paulsen’s Concept of “Match” in Saccharide Coupling
Three modes of selectivity — enantio, stereo, and regio — are critically important for efficient organic synthesis. In the sub-domain of oligosaccharide synthesis, the first is (usually!) irrelevant in view of the chiralities of the reacting partners. The challenge posed by the other two is compounded by the reality that “protecting groups” are the major, if not only, instruments by which control can be exercised. The role that O2 protecting groups play in stereocontrol of coupling reactions was formulated 60 years ago. In this microreview, evidence is presented which shows that O2 protecting groups also exercise regiocontrol. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)