Regioselective and stereoselective benzylidene installation and one-pot protection of d-mannose

Oligosaccharide syntheses are an important source of well-defined sugar constructs particularly needed for the evaluation of structure-activity relationships. The chemical assembly of oligosaccharides requires several building blocks, that is, glycosyl donors and acceptors, which are prepared in multistep processes and in a generally tedious and time-consuming manner. Having developed one-pot procedures meant to minimise the effort in sugar building block preparation, we tackled herein the one-pot preparation of fully protected and 2-, 3-, 4-, and 6-alcohol derivatives of d-mannose, a widely distributed monosaccharide. As a consequence of the hydroxyl group pattern of D-mannose, regioselective and stereoselective benzylidenations were developed and later seamlessly utilised as the first transformation in the one-pot procedure.