143291-31-0Relevant articles and documents
Condensation of Phenols and Cinnamic Acids in Presence of Polyphosphoric Acid: A Novel Biogenetic-type Oxidative Self-cyclisation of p-Methoxycinnamic Acid to 7-Methoxycoumarin
Talapatra, Bani,Deb, Tulika,Talapatra, Sunil
, p. 1122 - 1125 (2007/10/02)
The course of PPA condensation/cyclisation of different phenols and cinnamic acids has been found to depend upon the nature of the substrate, stoichiometry, composition of PPA, and reaction condition.Condensation of phloroglucinol (50-70 deg C, 1 hr) with cinnamic acid in the presence of PPA leads to pinocembrin (I) (50percent) and 5-hydroxy-4,8-diphenyl-3,4,6,7-tetrahydro2H,6H-benzodipyran-2,6-dione (II) (14percent).This condensation reaction when carried out with resorcinol for 2 hr furnishes 7-hydroxyflavanone (III) (60percent).Condensation of resorcinol monomethyl ether affords 2'-hydroxy-4'-methoxychalcone (IV) (12percent) and 4'-hydroxy-2'-methoxychalcone (V) (40percent), but no flavanone derivative.Reaction of p-methoxycinnamic acid (in xylene), in the presence of PPA and resorcinol, however, yields 7-hydroxy-4-(4'-methoxyphenyl)-3,4-dihydrocoumarin (VI) (56percent); with resorcinol monomethyl ether the corresponding 7-methoxy derivative (VII) (44percent) is obtained.Further, p-methoxycinnamic acid undergoes self-condensation in the presence of 0.5 mol equiv of phloroglucinol or resorcinol to give p-methoxycinnamic anhydride (VIII) (only 4percent) or bis(methoxybenzal)acetone (IX) (50percent).Interestingly, in the presence of resorcinol monomethyl ether (0.5 mol equiv, 4hr) p-methoxycinnamic acid undergoes biogenetic-type oxidative self-cyclisation to form 7-methoxycoumarin (X) (80percent).A plausible mechanism for the formation of X has been suggested.
