[CH3:1][O:2][C:3]1[C:4]([CH2:16][CH2:17][CH3:18])=[C:5]([CH:8]=[C:9]([N+:13]([O-:15])=[O:14])[C:10]=1[O:11][CH3:12])C=O.CC1C=CC(S(O)(=O)=O)=CC=1.CO[CH:32]([O:35][CH3:36])[O:33][CH3:34].[OH-].[K+]>CO>[CH3:12][O:11][C:10]1[C:3]([O:2][CH3:1])=[C:4]([CH2:16][CH2:17][CH3:18])[C:5]([CH:32]([O:33][CH3:34])[O:35][CH3:36])=[CH:8][C:9]=1[N+:13]([O-:15])=[O:14]A solution of the aldehyde from step (d) (14 g) tosic acid (0.2 g) and trimethylorthoformate (6.7 ml) in dry methanol (100 ml) was heated under reflux for 30 mins. A solution of potassium hydroxide in methanol (5 ml) was added to the reaction mixture and the solution evaporated to dryness. The residue was dissolved in ether, washed with water, dried, filtered and evaporated to leave a solid which crystallised from pentane as pale yellow prisms (11.6 g); mp 52.1°-54.0°.
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