Addition of cyanoacetamide to coumarins having substituents in the 3-position, such as the carbonyl, cyano and phenyl which are electronattracting, has been studied. Unlike alkyl groups and bromine atoms they do not in general inhibit addition. The following coumarins have been employed: (1) 3-acetyl-coumarin, (2) 3-benzoyl-coumarin, (3) 3-carbethoxy-coumarin, (4) coumarin-3-carboxylic acid, (5) 3-cyano-coumarin, and (6) 3-phenyl-coumarin. The speed of the reaction and the yield of the product depend upon (a) the activating capacity of the substituent group and (b) the readiness with which it can be eliminated under the experimental conditions. Compounds (1) and (2) give poor yields of the products; (3) combines with 2 molecules of cyano-acetamide; (4) resembles coumarin due to ready decarboxylation; (5) reacts without complications; (6) does not react. Among other additive compounds tested cyanoacetic ester reacts satisfactorily with 3-cyano-coumarin. 3-Acetyl-coumarin seems to undergo polymerisation and deacetylation to form dihydro-dicoumarinyl in the presence of piperdine.
Convenient methods for the preparation of 3-cyanocoumarin, coumarin-3-carboxylic acid and its piperidide have been investigated.