prov:value
| - e, toluene, hexane, cyclohexane or petroleum fractions, or other solvents such as nitromethane, ethyl acetate, acetone, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 2-butanone, dimethyl sulphoxide, acetonitrile or pyridine, preferably tetrahydrofuran or diethyl ether, optionally in the presence of a base, such as, for example, alkali metal carbonates such as caesium carbonate, sodium
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