Triphenylphosphine (4.08 g, 15.5 mmol) was dissolved in THF (25 ml), cooled to about 0° C. under N2 and Diethylazodicarboxylate (2.45 ml, 15.54 mmol) was added at a dropwise rate so that the reaction temperature was maintained at about <3° C. Stirring was continued for about 12 hour at 0° C. A mixture of the triphenylmethanethiol (4.30 g, 15.54 mmol) and the product from Step 13.e. (2.90 g, 7.77 mmol) in THF (25 ml) was added at a dropwise rate. The resulting mixture was stirred for about 1 hour at about 0° C. and then allowed to warm to room temperature. The mixture was concentrated under reduced pressure and the residue dissolved in ether (40 ml) and allowed to stand overnight. The solid was filtered off and the filtrate was concentrated then purified by flash chromatography on silica gel using 4:1/hexanes:EtOAc and then 4:1/hexanes:EtOAc as eluants. The product fractions were combined and concentrated under reduced pressure to obtain a pale yellow foam (5.49 g, 111%) which was used without further purification. Mass spec. 632.4 MH+.
