Enantiomerically Pure 7-Oxabicyclo(2.2.1)Hept-5-En-2-Yl Derivatives (Naked Sugars) as Synthetic Intermediates .25. Total Asymmetric-Synthesis of 3-Amino-3-Deoxy-L-Talose and Derivatives
(1R,2R,4R)-2-exo-Cyano-7-oxabicyclo[2.2.1]hept-5-en-2-yl (1S')-camphanate [(+)-1, Diels-Alder adduct of furan to 1-cyanovinyl (1S)-camphanate] was transformed with high stereoselectivity into (1R,2R,6R,7R)-4-phenyl-3,10-dioxa-5-azatricyclo[220.127.116.11(2,6)]dec-4-en-9- one [(+)-10]. Bromination of the corresponding (tert-butyl)dimethylsilyl enol ether [(-)-11], followed by Baeyer-Villiger oxidation and then alkaline methanolysis provided methyl 3-amino-1,5-anhydro-2-O,3-N-benzoyl-3-deoxy-alpha-L-talofuranuronate [(-)-17], the reduction of which gave 3-amino-1,5-anhydro-2-O,3-N-benzoyl-3-deoxy-alpha-L-talofuranose [(-)-19]. Treatment with aqueous HCl furnished 3-amino-3-deoxy-L-talose hydrochloride [(-)-2].