Protected forms of exo-5-amino-exo-6-hydroxy-7-oxabicyclo [2.2.1]heptan-2-one and of exo-5-amino-endo-6-hydroxy-7-oxabicyclo[2.2.1]heptan-2-one can be obtained readily and with high stereoselectivity from exo-2-cyano-7-oxabicyclo[2.2.1]hept-5-en-2-yl acetate (+/-)-(7). The processes involve acid promoted rearrangements of N-carbonyl aziridines 10 [(1RS,2SR,4RS,5RS, 6SR)-6-cyano-8-oxa-3-azatricyclo[3.2.10(2,4)]oct-6-yl acetate derivatives] derived from (+/-)-7.