Photochemistry synthesis. Part 2: Enantiomerically pure polyhydroxy-1,1,3-triarylpropan-2-ols

A new method to open the heterocyclic ring of flavan-3-ols via photolytic cleavage of the ether bond, with stereoselective trapping of the intermediates with phloroglucinol to obtain phloroglucinol grafted derivatives of flavan-3-ols, was developed. Photolysis of catechin and epicatechin, respectively, in the presence of phloroglucinol yielded the enantiomeric (1S,2S)- and (1R,2R)-1,3-di(2,4,6-trihydroxyphenyl)-1-(3,4-dihydroxyphenyl)propan-2-ols, respectively. The absolute configuration at C-1 and C-2 was determined by electronic circular dichroism (experimental and calculated) and these results confirmed that the trapping mechanism is controlled by the C-3 configuration of the flavan-3-ol.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Novel photolytic cleavage of the ether bond of the heterocyclic ring of flavan-3-ols. ► Stereoselective trapping of the intermediates with phloroglucinol to yield 1,1,3-triarylpropan-2-ols. ► Determination of the absolute configuration of the 1,1,3-triarylpropan-2-ols via the comparison of calculated and experimental ECD spectra. ► It was demonstrated that the trapping mechanism is controlled by the C-3 configuration of the flavan-3-ol. ► Both the (R,R) and (S,S) enantiomers of the grafted phloroglucinol products were accessible.