Synthesis and photoinitiated thiol-ene reactions of exo -mannals - a new route to C -β-d-mannosyl derivatives.

Syntheses of acyl protected exo -mannal derivatives were developed starting from O -peracylated mannopyranoses via the corresponding anhydro-aldose tosylhydrazones under modified Bamford-Stevens conditions. The synthesis of analogous O -peralkylated (benzylated and isopropylenated) derivatives was carried out from pyranoid and furanoid mannonolactones using methylene transfer reagents. Photoinitiated thiol-ene additions of these exo -mannals resulted in the corresponding C -(mannopyranosyl/mannofuranosyl)methyl sulfides in medium to good yields with exclusive regio- and β(d) stereoselectivities.