Halogenated coumarins

Halogenation. Coumarin reacts with bromine under moderate conditions to give 3,4-dibromocoumarin [42974-18-5] (24). The 3-bromocoumarin [939-18-4] and 3,6-dibromocoumarin [58309-97-0] are formed under more drastic conditions (25). 3-Chlorocoumarin [92-45-5] is formed by reaction with chlorine in dichloroethane (26) or without solvent (27). 

This compound is heated with caustic potash solution, yielding beta-hydroxy-coumarin. From this body, coumarin is obtained by substituting a halogen atom for the OH group, and then reducing the product in alcoholic solution with zinc-dust. 

Whereas benzopyrylium salts are resistant to electrophilic substitution, even in the benzene moiety, the benzopyrones [coumarins (81), isocoumar-ins (82), and chromones (83)] are readily halogenated in either ring, with... 

Quinolin-4-one forms a 3-bromo derivative, but coumarin gives the addition compound (116) which is easily re-aromatized (116 — 117). 4-Thiopyrones are halogenated in position 3. Pyridazinones and cinnolinones are also readily halogenated in the expected position. 

Dieldrin halogenated hydrocarbon Dienochlor halogenated hydrocarbon Diethatyl-ethyl amide Diethofencarb carbamate Diethyltoluamide amide Difenacoum coumarin... 

Tetramethylcyclohexanes.—Six new esters of ferulol (162) have been detected in Peucedanum luxurians and spectroscopic evidence is provided for the presence of (163) as an ether group in the two new coumarins, iselin and iliensin, from Seseli iliense A halogenated member of this class is discussed in the halogenated monoterpenoids section. ... 

Other cosmetic ingredients, cited in the literature for phototoxic reactions, are 6-methyl coumarin (formerly used as a fragrance component of sun protection and facial products) and halogenated salicylanilides (previously used in antibacterial products such as deodorant soap bars) [188]. 

The action of promoting cell elongation by coumarin is related to the intact structure of the molecule [104]. Some derivatives have shown inhibition at the same concentrations at which coumarin exerted an activation. Particularly hydroxy substitution elicited this adverse effect, whereas methyl and halogen replacement only reduced the stimulatory action. Open ring derivatives, o-coumaric and melilotic (o-hydroxyphenylpropionic) acids, were also less active than coumarin [97]. 3- and 4-Hydroxycoumarins were not only inhibitors of growth stimulation but these compounds counteracted the enhancing action of coumarin. 

Borges, F. Pinto, M. Synthesis of coumarins and derivatives. Biomimetic synthesis of esculetin and halogenated derivatives. Helv. Chim. Acta 1992, 75, 1061-1068. 

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