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.

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► 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.