Hydrochloric Acid → (2Z,4E)-5-(5,6-dichloro-1H-indol-2-yl)-2-methoxy-2,4-pentadienoic acid

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Reaction Steps

A suspension of methyl (2Z,4E)-5-(5,6-dichloroindol-2-yl)-2-methoxy-2,4-pentadienoate (10 g, 30.7 mmol) and KOH (3.6 g, 64.2 mmol) in EtOH/water {fraction (1/1)} (460 ml) was refluxed for 3 h. The suspension after cooling to RT was poured into water (1.5 l), it was acidified with 2N HCl and extracted with AcOEt (2×1 l). The organic phase was washed with water and dried (MgSO4), then concentrated and the residue taken up with CH2Cl2. Filtration and drying in the oven at 50° produced 9.5 g of pure title compound (30.4 mmol, yield 99.1%), m.p.=249-250° C.

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