Synthesis of L-daunosamine and L-ristosamine glycosides via photoinduced aziridination. Conversion to thioglycosides for use in glycosylation reactions

Application of photoinduced acylnitrene aziridination to the syntheses of L-daunosamine and L-ristosamine glycosides is reported. Photoreaction of methyl 4-O-azidocarbonyl-2,3,6-trideoxy-L-hex-2-enopyranosides, followed by aziridine opening, leads to 3-amino-3-N-,4-O-carbonyl-2,3,6-trideoxy precursors to the aminosugar methyl glycosides. Conversion of these precursors to their thioglycoside analogues followed by N-acetylation of the carbamate moiety permits high yielding and, in some cases, stereoselective glycosylations using the 1-benzenesulfinylpiperidine-triflic anhydride activation method developed by Crich and co-workers. Glycosylations involving activation with N-iodosuccinimide and silver triflate were also successful, but the stereoselectivities of these reactions in general were lower.