7-Hydroxy-3,4-dihydrocoumarin

A recent example of zeolite-catalyzed esterification involving biochemicals is the reaction of aminoacids with methanol. For instance, L-phenylalanine was converted to its methyl ester over H-USY at 130°C. However, the chiral carbon atom was racemized to a considerable extent, yielding an eventual ee of 52% (27). In the reaction of a, (3-unsaturated acids with phenols, the esterification over H-Beta is followed by an alkylation of the aromatic ring for instance resorcinol and acrylic acid react to form 7-hydroxy-3,4-dihydrocoumarin (28). 

I-3i ,II-350-fe -4-(4 -hydroxy)phenyl-7-hydroxy-3,4-dihydrocoumarin (282) (I-3, II-3 )-6/5-4-(4 -hydroxy)phenyl-7-hydroxy-3,4-dihydrocoumarin (283)... 

Dry HCl bubbled through a well-stirred ice-cold soln. of resorcinol and a-phenyl-acrylonitrile in dry ether with portionwise addition of ZnClg, stirred 2-3 hrs. in the cold, kept 3-5 days in the refrigerator, the ether decanted off, the residue treated with cold dil. HCl, heated on a steam bath, and the resulting 3-phenyl-7-hydroxy-3,4-dihydrocoumarin refluxed 5-6 hrs. with 10%-Pd-C in diphenyl ether 3-phenyl-7-hydroxycoumarin. Overall Y 60-65%. F. e. s. A. K. Das Gupta and M. S. Paul, J, Indian Chem. Soc. 47, 1017 (1970) s. a. D. K. Chatterjee and K. Sen, ibid. 48, 387 (1971),... 

M.C. Laufer et al. published the synthesis of hymecromone from resorcinol and EAA in toluene using a nanocatalyst, namely, Nafion resin/silica nanocomposite materials with yield between 81% and 96% (03MI315). The reaction of resorcinol with acrylic acid gives 7-hydroxy-3,4-dihydrocoumarin 36 and [l,2-k5,4-l>]dipyran-2,8-dione 37. The mechanism involves esterification followed by ring closure that ring closure is faster than the Fries rearrangement. Also in this reaction, SAC 40 and SAC 80 led to the best results (Scheme 23) (03MI315). 

The compounds covered in this section include dihydropyranones, tetrahydropyranones and their benzologues (dihydrocoumarins, chromanones and isochromanones). The area of greatest interest is undoubtedly the chromanones because of their relationship to a number of natural products and presumably also because of their ease of formation, stability and value as precursors of other heterocycles. Tetrahydropyran-2-ones comprise one of those nebulous areas of heterocyclic chemistry and usually feature in text books as 5-lactones under derivatives of hydroxy acids. 

SYNS 1,2-BENZODiHYDROPYRONE (FCC) 2-CHROMANONE DIHYDROCOUMARIN 3,4-DIHYDROCOUMARIN o-HYDROXY-HYDROCIN-NA.MIC ACID-A-LACTONE FEMA No. 2381 MEULO-TIN MELILOTOL NCI-C55890 2-OXOCHROMAN... 

Reduction of coumarins to the dihydro-derivatives has frequently been achieved, but a more efficient procedure has emerged from a new study of this conversion. The most effective method was catalytic reduction in ethanol at 150 °C and under a high pressure (1500 psi) of hydrogen of give mostly the 2-hydroxy-3-phenylbutanoate, which was readily cyclized with PPA to the dihydrocoumarin. Hydroboration of 3-arylcoumarins, followed by oxidation, gave isoflavanones the latter have been dehydrogenated (with DDQ) to isoflavones. A reaction of wide potential value is the selective hydrolysis by zinc and methanol of phenolic acetates in the presence of aUphatic acetate groups. 

Chromanol, 2,5,7,8-tetramethyl-2-(4,8,12-trimethyl tridecyl)-. See DL-a-Tocopherol 6-Chromanol, 2,5,7,8-tetramethyl-2-(4,8,12-trimethyltridecyl)-, acetate. See dl-a-Tocopheryl acetate 2-Chromanone. See Dihydrocoumarin ChromaOne . See Urethane-acrylate resin Chromasisi 87H, Chromasist 1487A. See Sodium polynaphthalene sulfonate Chromate(5-), bis (2-((4,5-dihydro-3-methyl-1-(2-methyl-4-sulfophenyl)-5-oxo-1H-pyrazol-4-yl) azo)-4-sulfobenzoato(4-))-, tetrasodium hydrogen. See Acid yellow 54 Chromate(3-), bis (3-hydroxy-4-((2-hydroxy-1-naphthalenyl) azo)-7-nitro-1-naphthalenesulfonato (3-))-, disodium hydrogen. See Acid black 52 Chromate (2-), (5-chloro-3-((4,5-dihydro-3-methyl-5-oxo-1-(3-sulfophenyl)-1H-pyrazol-4-yl) azo)-2-hydroxybenzenesulfonato (4-)) hydroxy-, disodium. See Acid red 183 Chromate copper arsenate CAS 11125-95-4... 

Environmentally benign synthesis routes for umbelliferone (I), 7-hydroxy-4-methylcoumarin (II), 3,4-dihydrocoumarin (III), and tricyclic coumarin (IV) (Figure 10.2) were developed using zeolite-H-p or Amberlyst-15 as solid catalysts. This resulted in the minimization of harmful mineral acid wastes. The reactions of resorcinol with acrylic acid, propynoic acid, and ethyl acetoacetate were investigated in toluene and p-chlorotoluene under reflux conditions to obtain coumarins in 60%-80% yield (Hoefnagel et al. 1995 Gunnewegh et al. 1995). 

FIGURE 10.2 Umbelliferone (I), 7-hydroxy-4-methylcoumarin (II), 3,4-dihydrocoumarin (III), and tricyclic coumarin (IV). 

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