Convenient Synthesis of 1,4-Dihydroxy-2-(ω-Hydroxyalkoxy)Anthracene- 9,10-Diones and their Conjugation with D-Glucal

Purpurin, 1,2,4-trihydroxyanthraquinone, was regioselectively alkylated under basic conditions using bromoalcohol of varying chain length. As a base, potassium carbonate, tetrabutylammonium hydroxide or 1,8- diazabicyclo[5.4.0]undec-7-ene (DBU) was used. The reaction of alkylation proceeded exclusively on the 2-hydroxyl group of the purpurin molecule. Addition of the obtained 2-(ω-hydroxyalkoxy)purpurins to protected D-glucal catalysed by triphenylphosphine hydrobromide gave an access to new glycoconjugates with high enantioselectivity. In parallel experiments, the same substrates reacted in the presence of boron trifluoride etherate yielding the appropriate unsaturated adducts as a result of Ferrier rearrangement.