Pyrano-coumarins

The linear (psoralens) and angular (angelicins) fur-anocoumarins can be readily differentiated with the Emerson reagent. It is used, also, for detection of pyrano-coumarins (selinidin, pteryxin) on TLC chromatograms. 

The fruits of Ammi visnapya contain the pharmacologically active chromone (khellin) and pyrano coumarins (visnadin). 

B In UV-36.5 nm, the un.sub,stituted coumarin, in contrast to coumarins with -OH, -OCH,, sLib,stituents or fiirano- or pyrano-coumarins, shows a typical green-blue fluorescence only after treatment with KOH reagent. Scopoletin (Tl) and umbelliferone (T3) are present in low concentrations only, seen as blue fluorescent zones at Rj 0.25 and 0.4, rc.spcctively (1-3). 

Pyranocarbazoles like girinimbine (3) can be detected readily by the formation of an immediate blue colour with BF3-etherate (16). Pyrano-coumarins like seselin (4) (32) do not respond to this test. 

B. Karami, S. Khodabakhshi, K. Eskandari, A new application of Mohr s salt as a cheap and powerful catalyst for s)mthesis of novel pyrano-coumarins, Lett. Org. Chem. 10 (2013) 105-110. 

A minor product isolated in studies of the sulphmization of the pyrano-coumarin (37) is thought to be a member of the dioxathiapentalene series. ... 

The Knoevenagel reaction between o-hydroxyaryl aldehydes and ketones and substituted acetonitriles affords high yields of 3-substituted coumarins in aqueous alkaline media <96H(43)1257>, whilst 4-hydroxycoumarins have been elaborated to pyrano [3,2-c]benzopyran-5-ones by reaction with aromatic aldehydes and malononitiile <96P148>. The imine (10) resulting from the complex reaction of o-hydroxyacetophenone with malononitrile undergoes a 1,5-tautomeric shift in solution <96JCS(P1)1067>. 

Hydroxycoumarins and 4-hydroxyquinolinones have also been applied as 1,3-dicarbonyl compounds. Using these compounds, Raghunathan and coworkers prepared pyrano[3,2-c]coumarins [387] and pyranoquinolinones [388] under traditional conditions, while the group of Yadav synthesized similar pyrano[3,2-c]coumarins employing ionic liquids as solvents [389]. 

In order to study any chemoselectivity influences of microwave irradiation on the domino Knoevenagel/hetero-Diels-Alder process (the so-called Tietze reaction), Raghunathan and coworkers [31a] investigated the transformation of 4-hydroxy coumarins (10-85) with benzaldehydes 10-86 in EtOH to afford pyrano[2,3-c]cou-marin 10-87 and pyrano[2,3-b]chromone derivatives 10-88. Normal heating of 10-85a and 10-86a at reflux for 4h gave a 68 32 mixture of 10-87a and 10-88 in 57% yield, whereas under microwave irradiation a 97 7 mixture in 82% yield was obtained. Similar results were found using the benzo-annulated substrates 10-85b and 10-86b. 

The synthesis of 186 with a 3-thioamide substituent (93ZOR1465) succeeded. Several pyrano[3,2-c]coumarins 186 and their derivatives possessing promising antibacterial and fungicidal activity were also synthesized (01MOL519, 03MOF275). 

The reaction was studied on nonannulated aminopyrans (89M1101), tetrahydrochromenes, naphtha[2,l-b]pyrans (04MI2), pyrano[3,2-/j]quino-lines (91BCJ668), pyrano[3,2-c]coumarines (01MOL519, 03MOL275), and... 

Coumarins (chromen-2-ones) and furo- and pyrano-chromenones, mass spectra of ... 

The Pd-catalysed Miyaura-Suzuki coupling of aryltrifluoroborates with 4-tosyloxycoumarins in aqueous conditions offers an attractive route to 4-arylcoumarins <06TL1525> and 4-hydroxycoumarins have been converted into a mixture of predominantly thiopyrano[5, 4 3,4]- pyrano[5,6-c]coumarins and [6,5-c]chromones in a one-pot tandem Knoevenagel - HDA sequence with an S-prenylated 1-phenyl-lff-pyrazole-4-carbaldehyde <06TL2265>. The benzopyrano[4,3-c]benzopyranone system can be obtained from 3-aryl-4-methylcoumarins by deprotonation of the methyl function and subsequent elaboration <06TL5909>. 

The value of 4-hydroxycoumarin in synthesis has been discussed <07THC(11)283> and its use in the synthesis of 3,4-disubstituted coumarins has been reported <07JOC7279>. The 3-arylation of 4-hydroxycoumarins, achieved using aryllead triacetates, sets up a substrate for a cascade of reactions which leads to the [2]benzopyrano[4,3-c][l]benzopyran system <07JOC3293> and the EDDA-catalysed reaction of 4-hydroxycoumarin with a,[3-unsaturated arylaldehydes produces pyrano[3,2-c]benzopyran-5-ones <07T10025>. Propargylation and... 

A variety of 2-substituted 2//-chromenes can be obtained from the facile reaction of 2-hydroxybenzaldehydes with vinylboronic acids in ionic liquid solvents <04SL2194>. In a one-pot sequence also in an ionic liquid, a Knoevenagel condensation between O-prenylated salicylaldehydes and 4-hydroxycoumarins is followed by an intramolecular hDA reaction to yield ci5-fused chromano[4, 3 4,5]pyrano[3,2-c]coumarins e.g. 20 small amounts of the corresponding chromone are also formed <04S1783>. In like manner, cii-fused furopyranopyran derivatives have been obtained from sugar aldehydes <04TL3493>. 

Cycloalka[6]pyrano[2,3-/7]coumarins are formed when the chloroethylidene derivative 48, produced by the reaction of cycloalkanols with thionyl chloride, reacts with a... 

Hydroxycoumarin and formaldehyde are a source of the o-quinone methide, 3-methylenechroman-2,4-dione, a good Diels-Alder substrate which yields pyrano[3,2-c]coumarins regio- and chemo- selectively with unsymmetrically substituted alkenes (94JOC5556). 

Chemoselectivity has been achieved when MWI was used for the synthesis of pyrano[3,2-c]coumarins through intramolecular domino Knoevenagel hetero Die-Is-Alder reactions of 4-hydroxycoumarin (103). Thus, when the reaction of 103 with butenyloxyaldehyde 76 was carried out under MWI for 10-15 s, cycloadducts 112 and 113 were produced in 93 7 ratio, respectively, with 82% overall yield and the cycloadducts 115 and 116 were obtained in a ratio 95 5, respectively, in 92%... 

Sulfur analogs of fluorinated chromones and coumarins 13JSC432. Supramolecular photodimerization of coumarins 12MOL1408. Synthesis and chemical reactivity of pyrano[3,2-c]quinolinones 12JHC 1269. 

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