Pyrano chromen-5-ones

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

Domino Knoevenagel hetero-Diels-Alder reaction of 1 with sugar aldehyde 489 gave, in a stereoselective manner, the fused furo[2, 3 5,6]-pyrano[3,4-c]chromen-l-one 491 presumably via the aldehyde adduct 490 (04TL3493, 04S1150) (Scheme 104). 

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>. 

However, when 36 was heated with a-amino heterocycles or with cyclic 1,3-dicarbonyl or potential 1,3-dicarbonyl compounds, 3-heteroarylp)rr-azol derivatives were obtained. In this manner 36 afforded, when heated with 2-aminopyridine and 3-amino-lH-pyrazol in acetic acid under reflux for 2 h and 5 h, respectively, 3-(5-ethoxy-l-phenyl-lH-pyrazol-3-yl)-4H-pyrido[l,2-fl]pyrimid-4-one (38) and 6-(5-ethoxy-l-phenyl-lH-p5rrazol-3-yl)pyrazolo[l,5-fl]pyrimid-7(lH)-one (39) in 70% and 77% 5deld, respectively. Similarly, 36 afforded with cyclicjS-dicarbonyl compounds, such as 4-hydroxy-6-methyl-2H-pyran-2-one and 5,5-dimethylcyclohexane-l,3-dione by heating in acetic acid for 4 h and 8 h, respectively, the corresponding 3-(5-ethoxy-l-phenyl-lH-pyrazol-3-yl)-7-methyl-2H,5H-pyrano[4,3- 7]pyran-2,5-dione (40) and 3-(5-ethoxy-l-phenyl-IH-pyrazol-3-yl)-7,7-dimethyl-7,8-dihydro-2H-chromene-2,5-dione (41) in 26% and 82% yield, respectively (Scheme 15). 

Pyrimidines 73 with dinucleophiles, such as 2-amino-pyridine, 1,3-dimethylbarbituric acid, 5,5-dimethylcyclohexa-l,3-dione and 4-hydroxy-6-methyl-pyran-2(lH)-one, were carried out in boiling acetic acid formed 4H-pyrido[l,2-fl]pyrimidin-4-one (76), lH-pyrano[2,3-d]pyrimidine-2,4,7(3H)-trione (77), 6H-chromene-2,5-dione (78) and pyrano[4,5-b]pyran-2,5-dione (79) in 30%, 67%, 56% and 73% yields, respectively (Scheme 26). 

J. Kamalraja, D. Muralidharan, P. T. Perumal, Synlett 2012, 23, 2894—2898. An efficient, one-pot regioselective synthesis of highly functionalized chromene-5-ones and pyrano[3,2-c] chromene-5-ones via a tandem Knoevenagel-Michael-cycli-zation sequence. 

A solution of cyclic 1,3-dicarbonyl compound (1 1.0 mmol)/ 4-hydroxycoumarin (5 1.0 mmol), arylaldehyde (2 1.0 mmol), NMSM (3 1.0 mmol), and piperidine (20 mol%) in etahnol (2 mL) was stirred at room temperature for the appropriate time (2-5 h). On completion of the reaction (as indicated by TLC), the product (4/6) was filtered and washed with etahnol (2 mL) to remove the excess base and other impurities. Pure chromen-5-ones (4)/pyrano[3,2-c] chromen-5-ones (6) were obtained when recrystallized from EtOH. All the products were characterized from spectral (IR, NMR, NMR, MS) and elemental analyses. 

Recently, Brahmachari and his group [133] have developed a simple, facile, and convenient practical method for one-pot syntiiesis of pharmaceutically interesting diverse kind of pyran-annulated heterocycles such as 4H-pyrano[3,2-c]coumarins (14), 4H-pyrano[3,2-c]-a-pyrones (12), 5,6,7,8-tetrahydro-5-oxo-4H-chromenes (9), and benzo[//]-4H-chromenes (8) in the presence of ammonium or sodium formate as catalyst via three-component... 

Gold-catalyzed cycloisomerizations of alkynyl ketones/aldehydes provide convenient access to 2-benzopyrylium salts, which are important intermediates for natural product syntheses. For example, the benzaldehyde derivative 151 was converted directly to the 2-benzopyrylium salt 152 in the presence of a catalytic amount of Au(OAc)3 in (CH2C1)2/TFA (Scheme 19.37) [62], IBX-mediated oxidation of 152 in the presence of n-Bi NI (as a phase-transfer catalyst) cleanly afforded the azaphilone 153 in 84% yield after reductive workup, which is a precursor of ( )-S-15183a (154). Similarly, AgNOs-promoted cyclization of the alkyne 155 furnished direct construction of the tricyclic 8/7-pyrano[2,3,4-rfe]chromen-8-one core of cassiarin A (158) (Scheme 19.38) [63]. 

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