Tautomer A: In a round-bottom flask, a mixture of aq. KOH (7 M, 15 mL, 24 equiv.) and EtOH (15 mL) was cooled down to 5 °C using an ice-water bath. Acetyl phloroglucinol S-3 (1.70 g, 4.94 mmol, 1.0 equiv.) and benzaldehyde (1.00 mL, 1.05 g, 9.87 mmol, 2.0 equiv.) dissolved in EtOH (15 mL) were added slowly. Then, the mixture was allowed to warm up to RT. After stirring the mixture at this temperature for 16 h, more benzaldehyde (1.00 mL, 1.05 g, 9.87 mmol, 2 equiv.) was added. Stirring was continued for 7 h. Then, more benzaldehyde (1.00 mL, 1.05 g, 9.87 mmol, 2 equiv.) was added. After another 16 h the starting material was consumed completely. The mixture was poured into an ice-cold sat. aq. solution of ammonium chloride (100 mL) and extracted with EtOAc (3 x 100 mL). The combined organic layers were washed with water, brine, dried over Na 2 SO 4 , filtered and concentrated under reduced pressure. The residue was dried while stirring under high vacuum for 3 h to remove parts of the excess benzaldehyde. The crude product was purified by column chromatography (SiO 2 , Et 2 O/pentane, 1:19). After purification, the product was once more dried while stirring under high vacuum over night to remove the remaining traces of benzaldehyde to afford cinnamoyl phloroglucinol 9 (1,73 g, 4.00 mmol, 81%) as a yellow, thick oil.