Furo benzopyrans

The alkaloid reserpiae [50-55-5] which is isolated from the roots of Kauwoljia serpentina T., contains a gaUate trimethyl ether moiety. Reserpiae is used as an antihypertensive and a tranquilizer. A vinylogue of reserpiae, rescinnamine [24815-24-5] is also an antihypersensitive (75). Methoxsalen [298-81-7] (8-methoxypsoralen 7JT-9-methoxy-furo [3,2- ] [l]benzopyran-7-one) (21), a furocoumatia that occurs ia plants, eg, l eguminosae and Umbelliferae is used ia the treatment of vitiligo, as a suntanning promoter, and as a sunburn protectant. It is also available by synthesis (76). 

Trioxsalen (2,5,9-trimethyl-7H-furo[3,2-g]benzopyran-7-one) [3902-71-4] M 228.3, m 233-235 , 234.5-235 . Purified by recrystn from CHCI3. If too impure it is fractionally crystd from CHCl3-pet ether (b 30-60°) using Norit and finally crystd from CHCI3 alone to give colourless prisms, m 234.5-235°. It is a photosensitiser so it should be stored in the dark. [UV Kaufmann J Org Chem 26 117 1961-, Baeme et al. J Chem Soc 2976 1949.]... 

Visnagin (4-methoxy-7-methyI-5tf-furo[3,2-g][l]benzopyran-5-one) 142-145 . Crystd from water. 

Therapeutic Function Dermal pigmentation enhancer Chemical Name 9-methoxy-7H-furo[3,2-g] [1 ] benzopyran-7-one Common Name 8-Methoxypsoralen ammoidin xanthotoxin Structural Formula ... 

Furthermore, the Wu group [141] has prepared isoquinolines and iso-indoles starting from 2-(2-phenylethynyl)-benzonitrile, while Yamamoto and coworkers [142] prepared benzopyrans from alkynylbenzaldehydes, the Cacchi group [143] synthesized benzofurans, and Balme and coworkers [144] furo[2,3-fo]pyridones. 

The ancient Egyptians used the plantAmmi majus, which contains methoxsalen (sometimes called 8-methoxypsoralen, based on a now obsolete method of naming fused heterocycles indexed in Chemical Abstracts under furo[3,2-g][l]benzopyran-7-one, 9-methoxy-, 249), in combination with sunbathing to... 

A series of 3-alkyl- and 3-aryl-7/7-furo[3,2- ]-l-benzopyran-7-ones 78 (linear furocoumarins) was synthesized and evaluated for their photochemical and nonphotochemical crosslink formation with DNA as well as for their spectro-photometric and fluorescent properties, lipophilicity, and ability to photobleach A, A -dimethyl-/)-nitrosoaniline (RNO) after irradiation with UVA light <2002AP187>. The synthesis of the linear furocoumarins (Scheme 10) was a modification of a previously published method in which 7-hydroxy-2//-l-benzopyran-2-ones 76 were converted into / -ketoethers 77 by alkylation with haloketones under phase-transfer catalysis conditions. Base-catalyzed intramolecular condensation and subsequent acidification gave the corresponding 78. A molecular complex between each one of these fluorescent furocoumarins and DNA was observed, but only compounds with a 3-Me or 3-Ph group showed UVA irradiation-induced crosslink formation. 

The photocyclodimerization of coumarin (2//-l-benzo[b]pyran-2-one) in direct and sensitized experiments is known to proceed rather inefficiently in the absence of Lewis acids and in better yields in their presence.42,43 In contrast, 2-quinolone (22, X = NH)44 or 1-thiocoumarin (2//-l-benzo[b]thiopyran-2-one 22, X = S)45 afford anti head-to-head dimers 23 on direct irradiation in very good yields. Psoralens (7//-furo[3,2-g][l]benzopyran-7-ones) usually exhibit a behavior similar to that of coumarins.46... 

Other furocoumarins, although they have rather different structures, have very similar names, which gives rise to confusion. Thus, whereas oroselone (8) is 8-isopropenyl-2//-furo[2,3-A][l]benzopyran-2-one12 and oroselol (9) is 8-(l-hydroxy-l-methylethyl)-2 -furo[2,3- ][l]benzopy-ran-2-one, oreoselone (10) is 2-isopropyl-2,3-dihydro-7 -furo[3,2-gr][l]-benzopyran- 3,7- 2 -dione.13... 

Examples of polycyclic compounds with several heterocyclic rings include aflatoxin B (48)153 (2,3,6aa,9aa-tetrahydro-4-methoxycyclo-penta[c]furo[3, 2 4,5]furo[2,3-A][l]benzopyran-l,l 1-dione) which is... 

Coumarinyloxy-2-butanones, obtained from suitable Bz-hydroxy-coumarins, can be dehydrated (with H2S04) to furocoumarins (e.g., 8-ethyl-7-hydroxy-4-methylcoumarin gives 9-ethyl-2,3,5-trimethyl-7.ff, furo[3,2-g][l]benzopyran-7-one (75).230... 

This method is suited to the synthesis of natural benzofuran derivatives karanjin (111, R = R = H) (a furoflavone) and pongapin (111, RR = 0-CH2-0) have been prepared in this way,201 as well as khellin (26).315 From the chromone acetaldehyde (112), visnagin (113) (4-methoxy-7-methyl-5//-furo[3,2-g][l]benzopyran-5-one) was synthesized.310... 

Furo[3,2-c][l]benzopyran-4-ones have been prepared either by acid catalyzed condensation of 4-hydroxycoumarin with a benzoin derivative (equation 11) (81IJC(B)614) or from 3-allyl-4-hydroxycoumarins on oxidation with osmium tetroxide/potassium periodate followed by cyclization of the intermediary aldehyde with PPA (equation 12) (79G109). 

When 3-(4-j -tolyloxybut-2-ynyloxy)[l]benzopyran-2-one 1 was heated under reflux in carefully purified chlorobenzene, the exclusive product, formed in 92% yield, was 1 -(p-tolyloxymethyl)pyrano[2,3-c][l]benzopyran-5(3i/)-one 2. The compound 2 was also the exclusive product when either xylene or ethylbenzene was used as solvent. However, when 1 was heated under reflux in chlorobenzene containing a catalytic amount of AIBN, 2 was obtained in 20% yield together with 80% of 2-methyl-l-(p-tolyloxymethyl)furo[2,3-c] [l]benzopyran-4-one 3. The compound 3 was the exclusive product when PEG-600, IV.lV-dimethylaniline, pyridine or ethylbenzene containing a catalytic amount of p-TsOH was used as solvent, the yields being 90,90, 80 and 90% respectively. 

BENZOPYRANO(3,4-b)FURO(2.3-h) (1)BENZOPYRAN-6(6aH)-OME, 1,2.12,12a-TETRAHYDRO-2-alpha-ISOPROPENYL-8.9-DIMETHOXY-... 

CYCLOPENTA(c)FURO(3,-2, 4.5)FURO(2,3-h)(l)BENZOPYRAN-l,ll-DI0NE.2,3.6a.9a-TETRAHYDRO-4-METHOXY-... 

Deprotonation of chromone 369 with lithium 2,2,6,6-tetramethylpiperidide followed by addition to aldehydes provided substrates which were converted directly to furo[3,4- ][l]benzopyran-9-ones (e.g., 371) upon acetal deprotection (Scheme 57) <2002S2341>. 

Rao PS, Reddy KV, Ashok D (2000) A facile synthesis of 7-(substituted aryl)-2-benzoyl-3-methyl-5H-furo[3,2-g] [l]benzopyran-5-ones and their antifeedant activity. Indian J Chem 39B 557... 

One of six chromenone glycosides isolated from the tubers of Eranthis hyemalis and structurally identified by a combination of FAB-MS and 2D (COSY, COLOC) NMR techniques was compound (15), a / -D-glucopyranoside of 7-(hydroxymethyl)-2,3-dihydro-2-(l-hydroxy-l-methylethyl)-4-methoxy-5/7-furo[3,2- ][l]benzopyran-5-one <91HCA611). 

In a TTN-mediated oxidative rearrangement route to certain linear pyranoisoflavones, the aurones (2-alkylidene-6,7-dihydro-4-methoxy-7,7-dimethyl-5//-furo[3,2- ][l]benzopyran-3(277),5-diones) (45 R1 = R2 = H, OMe) were obtained in low yields (Equation (20)) <89BCJ826,92H(34)505>. A signal at d 6.45 ppm in the H NMR spectrum due to the benzylidene proton was noted as being characteristic of the aurone system. 

Furo[3,4-/ ][l]benzopyran-9-ones are formed directly by deprotection of the acetal 18. The corresponding thiochromones behave similarly <02TL4507>. Incorporation of a trifluoromethyl group into chroman-4-ones can be effected through reaction of 2-trifluoromethyl-4ff-chromen-4-imines with malonic acid the acid serves as a methylating agent <02S2341>. 

Dimethyl-t-butylsiloxy-7H-furo[3,2-g][l]benzopyran-7-one (General method for preparing silyl-protected Bergaptol)... 

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