β-Tricarbonyl compounds. Part 2. Synthesis of 5,7-dihydroxy-8-isobutyryl-2,2-dimethyl-2H-chromen and the antibiotics uliginosin B-iBiB and uliginosin B-iBiV

Abstract

Several routes to 5,7-dihydroxy-8-isobutyryl-2,2-dimethyl-2H-chromen were investigated and it was eventually prepared, together with the 6-isobutyryl isomer, by cyclodehydrogenation of 2′,4′,6′-trihydroxy-3′-(3-methylbut-2-enyl)isobutyrophenone using DDQ. A rottlerone exchange between the 8-isobutyrylchromen and albaspidin-iBiB then afforded uliginosin B-iBiB. Uliginosin B-iBiB and uliginosin B-iBiV have also been prepared by cyclodehydrogenation of the corresponding derivatives of uliginosin A. Natural uliginosin B contains a homologue (M+ 14) which is probably uliginosin B-iViB. 7-Hydroxy-2,2-dimethyl-2H-chromens react with DDQ to form 3-O-(2,3-dichloro-5,6-dicyano-4-hydroxyphenyl) ethers.