C-alkylation of methyl leuco-6-deoxykermesate by aldol reactions and its application to synthesis of carminic acid

In a non-aqueous medium in the presence of piperidinium acetate, methyl leu co-6-deoxykermesate reacts in aldol fashion with aldehydes regioselectively to give 6-alkyl products while under aqueous alkaline conditions over a pr olonged time, 7-alkyl compounds are selectively formed; the structures of t he 6-alkyl series was confirmed by an X-ray crystal structure determination of the 6-methyl member, namely methyl 3,5,8-trihydroxy-1,6-dimethylanthra- 9,10-quinone-2-carboxylate; in aqueous alkaline conditions during a short m ild reaction period, intermediate 7-alpha-hydroxyalkyl compounds can be iso lated, and in an application to a synthesis of 6-deoxycarminic acid, the al dol reaction of 2,3,4,5,6-penta-O-benzyl-D-glucose with methyl leuco-6-deox ykermesate was examined.