(3R,4S,5R)-3,4,5-tris-methanesulfonyloxy-cyclohex-1-enecarboxylic acid ethyl ester 43, product of the preceding experiment) was dissolved in DMSO. To the clear light yellow solution NaN3 was added at room temperature and the suspension was stirred for 3 hours. The orange solution was diluted with EtOAc and toluene and extracted 3 times with aqueous NaHCO3. The organic phase was separated, dried over Na2SO4, filtered and the combined filtrates evaporated in a rotary evaporator at 20° C./70-10 mbar. The remaining yellow oil was dissolved twice in toluene and evaporated in a rotary evaporator at 20° C./70-10 mbar to obtain the crude dry product (3R,4S,5R)-3-azido-4,5-bis-methanesulfonyloxy-cyclohex-1-enecarboxylic acid ethyl ester (44), as yellow oil which was used in purification. A sample of 4 was obtained from crude 44 via a silica column chromatography using a 1:2 mixture of EtOAc and n-hexane. The combined fractions were evaporated and dried on a rotary evaporator to obtain 44 as a pale yellow oil.
