Coumarin ring

One of the hits found in the Chem Inform reaction database is shown in the window for reaction substructure searches in Figure 10.3-55. It fits the synthesis problem perfectly, since in the synthesis direction it forms the coumarin ring system directly, in one step. 

Recently we have been able to produce coumarins by alkyne annulation in the presence of CO (Scheme 13).14 Production of the coumarin ring system is... 

The fluorescent properties of the coumarin ring system have already been described in the section on fluorescent chromophores 3.5.1.1 and not surprisingly colourless... 

A substantial listing of UV spectra of coumarins is available (71PMH(3)190) and examples of the identification of natural products based on the coumarin ring system by UV analysis, amongst other methods, have been reported (58JA3686,69MI22202). 

Further modification of the coumarin ring system in esculin (1) led to the development of 7-amino-4-methylcoumarins with an A-alkyl group at the 7-position. The sole representative of this series still on the market is 7-diethylamino-4-methylcoumarin (63) [91-44-1] [101], Despite its poor lightfastness, the good optical properties of this compound have kept it in use for the brightening of wool, cellulose acetate rayon, and polyamides. Compound 63 is produced by cyclocondensation of 3-diethylaminophenol with ethyl acetoacetate in the presence of zinc chloride [102],... 

Reactions of nitrogen and carbon nucleophiles have been found to proceed exclusively at an exocyclic C-l electrophilic center rather than at C-2 or C-4 of the coumarin ring for compounds such as 285 (Scheme 36). Though the yields are somewhat low, it was reported that no other products were observed other than those from C-l attack <2004SC3409>. 

Cupric sulfate Coumarin ring synthesis CuSQj o... 

Methyl resonances of a number of methylated furano-annulated coumarins have been reported (26, 27). The chemical shifts of methyl groups attached to the coumarinic rings correspond to the values in Table 3. Those, however, at C-2 are 8 = 14 (8 = 11.5 if there is another methyl group at C-3 ). Chemical shifts of methyl carbons at C-3 are 8 = 9.5 (8 = 8 if there is another methyl group at... 

Coumarin ring formation presumably by way of an intermediate imide accompanied the demethylation of the dinitrile shown with aluminium chloride in chlorobenzene by refluxing for 3.5 hours to afford a 96% yield of 3-cyano-5-hydroxy-7-pentylcoumarin (ref. 148). 

Coumarin and some of its methoxy-derivatives undergo acetoxymethylation, usually at C-3, in yields of up to 87% when heated with manganese(iii) acetate in a solvent such as acetic acid-acetic anhydride. Varying amounts of the 3-(diacetoxymethyl)-derivatives were also isolated in some experiments, and in the reaction with 7,8-dimethoxycoumarin the benzene ring was sufficiently reactive to allow the formation of 3,6-di(acetoxymethyl)-7,8-dimethoxy-coumarin. Ring-contraction of 4-(chloromethyl)coumarin in aqueous alkali proceeded in 92% yield to give benzofuran-3-acetic acid. " ... 

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