Synthetic Study on Carthamin: Problem and Solution for Oxidative Dearomatization Approach to Quinol C-Glycoside

Abstract

Synthetic study on carthamin, a natural red pigment, is described. Attempts at the construction of the key quinol C-glycoside structure by oxidative dearomatization of C-glycosyl phenols were hampered by the competing cleavage of the C1–C2 bond in the sugar moiety. By employing the 2-O-acetyl protection, the projected reaction proceeded smoothly, giving the desired products in good to excellent yields. An interesting photochemical stability/instability of the chalcone geometry in the synthetic compounds was observed.

Keywords

carthamin - quinol C-glycoside - oxidative dearomatization - chalcone - photoisomerization

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