Nosylate ester reduction

Nosyloxyesters undergo substitution reactions with inversion of configuration (Scheme 15). The corresponding nosyl lactate 98 is prepared in quantitative yield from 97 upon treatment with 4-nitrobenzenesulfonyl chloride in the presence of triethylamine and DMAP [34]. Reaction of 98 with sodium azide in DMSO (55 °C) gives the (R)-azidoester 99. Hydrolysis of the ester with lithium hydroxide in aqueous THF furnishes the azido acid 101 (92% ee). Reduction of the azide group is easily accomplished either under catalytic conditions or with triphenylphosphine and water. 

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