cis- and trans-Tetrahydroisohumulones

Abstract

Repeated acylation of phloroglucinol followed by intermediate reduction gave 4-deoxytetrahydrohumulone (VI), which was, by procedures of known type, converted into a mixture of (±)-cis- and (±)-trans-tetrahydroisohumulones [racemates of (XIX) and (XX) respectively]. The isomers were separated by chromatography and differentiated by their u.v. and 220 MHz n.m.r. spectra.

Several by-products were isolated and identified in the synthesis, including isobutyl 2′,3,4′,5,6′-pentahydroxybiphenyl-4-yl ketone (X) and 3,4-dihydroxy-2-isopentyl-4-(4-methylvaleryl)cyclopent-2-en-1-one (XVI).

Hydrogenation of a mixture of cis-(III) and trans-(IV) isohumulones obtained from (–)-humulone (II) gave, after separation, (–)-cis-(XIX) and (+)-trans-(XX) tetrahydroisohumulones, which, apart from their optical activities, were spectroscopically identical with the synthetic specimens.