Rheosmin (“Raspberry Ketone”) and Zingerone, and Their Preparation by Crossed Aldol-Catalytic Hydrogenation Sequences

Preparations of the two closely-related natural products rheosmin (“raspberry ketone”, 4-(4′-hydroxyphenyl)-2-butanone) and zingerone (4-(4′-hydroxy-3′-methoxyphenyl)-2-butanone), are well-suited for the introductory organic laboratory. The crossed-aldol condensation of 4-hydroxybenzaldehyde with acetone gives an adduct (4-(4′-hydroxyphenyl)-3-buten-2-one) which is hydrogenated cleanly over rhodium on alumina to form rheosmin. Condensation of vanillin with acetone gives 4-(4′-hydroxy-3′-methoxyphenyl)-3-buten-2-one, which is hydrogenated to zingerone. The article includes background information on the target compounds and the synthetic methods used, along with experimental procedures and IR and NMR data on the compounds encountered.