[O:1]=[C:2]1[O:6][CH2:5][N:4]([C:7]([O:9][CH2:10][C:11]2[CH:16]=[CH:15][CH:14]=[CH:13][CH:12]=2)=[O:8])[C@H:3]1[CH2:17][CH2:18][C:19](O)=[O:20].[Cr](Cl)([O-])(=O)=O.[NH+]1C=CC=CC=1>C1COCC1.C(Cl)Cl>[O:1]=[C:2]1[O:6][CH2:5][N:4]([C:7]([O:9][CH2:10][C:11]2[CH:12]=[CH:13][CH:14]=[CH:15][CH:16]=2)=[O:8])[C@H:3]1[CH2:17][CH2:18][CH:19]=[O:20]A solution of 27 g (92.7 mmol) of the crude acid (43c) in 200 mL of THF is cooled to 0° C. and 13 mL (10.7 g, 141 mmol) of borane-methyl sulfide complex is added dropwise via an addition funnel. The reaction is allowed to warm gradually to room temperature and stirred for 12 h. The resulting mixture is concentrated in vacuo to give a white glassy material which is taken up in 500 mL of methylene chloride and treated with of pyridinium chlorochromate (61 g, 281 mmol) at 0° C. in the presence of 3 -- molecular sieve. The mixture is allowed to warm to room temperature and stirred for 3 h. The mixture is filtered through diatomaceous earth with ether (200 mL) then concentrated. The residue is taken up in ether and filtered again through diatomaceous earth with ether then concentrated to give 13.22 g of the crude aldehyde as a light green oil: NMR δ9.80 (br s, 1H), 7.40 (m, 5H), 5.55 (br s, 1H), 5.20 (m, 3H), 4.38 (t, J=6.0 Hz, 1H), 2.6-2.1 (m, 4H).
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