Modified coumarins. 13. Synthesis of cyclopentane-annelated pyranocoumarins

Abstract

Modified pyranocoumarins containing a condensed cyclopentane fragment were synthesized by adjoining a 2,2-dimethyltetrahydropyran ring to a 2,3-dihydrocyclopenta [c]chromen-4-one system and annelation of a pyrone ring to a 2,2-dimethylchromane.Pyranocoumarins (chromeno-α-pyrones) are widely distributed in nature and contain a 2,2-dimethylpyran ring annelated to a benzopyran-2-one system at the 6,7; 5,6; or 7,8 positions [1]. Most natural pyranocoumarins are derivatives of the linear pyranone xantiletin (1) or its angular isomer seselin (2).Pyranocoumarins also include coumarins with a condensed 2,2-dimethyldihydropyran ring or an annelated 2,2-dimethyltetrahydropryan-4-one moiety. Typical representatives of natural 8,8-dimethyl-7,8-dihydropyrano[3,2-g]chromen-2-ones are dihydroxantiletin (3) isolated from Seseli tortuosum [2], Ammi majus [3], and Cassia pumila [4]; kanzonol Q (4) produced by Glycyrrhiza uralensis [5]; and isoglycycoumarin (5) isolated from Glycyrrhiza aspera [6,7], G. inflata, G. glabra, and G. uralensis [8].Examples of metabolites based on 8,8-dimethyl-7,8-dihydropyrano[3,2-g]chromen-2,6-dione are graveolone (6) produced by Anethum graveolens [9][10][11][12] and Pituranthos tortuosus [13] or clausenine (5-hydroxygraveolone) (7) isolated from Clausena heptaphylla and C. excavata [14][15][16].Our goal was to modify the structure of 2,3-dihydrocyclopenta[c]chromen-4-one by adjoining a 2,2-dimethylpyran ring. The cyclopentane-annelated dihydropyranocoumarins were synthesized by two methods: 1) addition of a 2,2-dimethyltetrahydropyran ring to the coumarin and 2) annelation of a pyrone ring to the 2,2-dimethylchromane core.Because they were necessary for further transformations, 7-hydroxy-6-methyl-2,3-dihydrocyclopenta[c]chromen-4-one (8) and 9-hydroxy-7-methyl-2,3-dihydrocyclopenta[c]chromen-4-one (9) were prepared by Pechmann condensation of 2-methylresorcinol and orcinol, respectively, with ethyl-2-oxocyclopentanecarboxylate in the presence of conc. H 2 SO 4 [17]. Condensation of 8 and 3,3-dimethylallylbromide in the presence of p-toluenesulfonic acid [18] gave the linear dihydropyranocoumarin 6,8,8-trimethyl-2,3,9,10-tetrahydrocyclopenta[c]pyrano[3,2-g]chromen-4-one (10). Using 9 in this condensation forms the angular isomer 2,2,5-trimethyl-3,4,10,11-tetrahydrocylopenta[c]pyrano[2,3-f]chromen-8-one (11). The results were analogous if 3-methyl-2-buten-1-ol instead of 3,3-dimethylallylbromide was used as the alkylating agent. PMR spectra of 10 and 11 show simplified splitting patterns for the aromatic protons compared with the starting coumarins owing to a lack of coupling for the benzopyran H-6 proton. For 10, H-11 is observed as a singlet at 6.99 ppm; for 11, H-6 at 6.73 ppm.

Insect Antifeedant Potential of Xanthohumol, Isoxanthohumol, and Their Derivatives

“…The spectroscopic data were consistent with those reported in the literature. 47,48 In the next step the purified product (2) was subjected to the Williamson ether synthesis with methyl iodide to give 7-methoxy-2,2-dimethylchroman-4-one (3), the spectroscopic data of which matched those reported by An et al 49 The synthesis of 4-hydroxychalcone (11) and 4-ethyl-4′-methoxychalcone ( 13) was carried out according to the literature method 50 under strongly basic conditions (KOH), using methanol as a solvent. Xanthohumol (14) was isolated using the earlier described method 51 from spent hops, the residue of supercritical carbon dioxide hop extraction, which was delivered by the Supercritical Extraction Department of the New Chemical Syntheses Institute in Puławy, Poland.…”

Synthesis and Structure Revision of Naturally Occurring Homoisoflavane (+)-Dracaeconolide B

“…For synthesis of 2, the treatment of benzylidene 13 with BCl 3 resulted in C-5 demethylation, followed by Clemmensen reduction of the carbonyl at C-4 to afford 2 containing the 5hydroxy-7,8-dimethoxy moiety. 18 The carbonyl at C-4 in 14 was not removed under H 2 and Pd/C, and this could be attributed to the presence of the C5-hydroxy. The C4-carbonyl and the 3,9-double bond in 13 were reduced, and C-4′ debenzylation was achieved under conditions of catalytic hydrogenation to provide 15.…”

“…Catalytic hydrogenation of 8 and subsequent aldol condensation with 4-(benzyloxy)­benzaldehyde afforded the homoisoflavanoid skeleton. For synthesis of 2 , the treatment of benzylidene 13 with BCl 3 resulted in C-5 demethylation, followed by Clemmensen reduction of the carbonyl at C-4 to afford 2 containing the 5-hydroxy-7,8-dimethoxy moiety . The carbonyl at C-4 in 14 was not removed under H 2 and Pd/C, and this could be attributed to the presence of the C5-hydroxy.…”

Phytochemical and Pharmacological Aspects of Psoralen – A Bioactive Furanocoumarin from Psoralea corylifolia Linn.

“…These derivatives were evaluated for fungicidal activity against Botrytis cinerea [110] . Figure 4B represents other psoralen derivative compounds which were synthesized from the starting material resorcinol [111] . Figure 4C represents some of the representative derivatives synthesized by Buhimischi et al.…”