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Synthesis of Coumarins and Derivatives. Part 1. Biomimetic synthesis of esculetin and halogenated derivatives
Author(s) -
Borges Fernanda,
Pinto Madalena
Publication year - 1992
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19920750409
Subject(s) - chemistry , caffeic acid , cinnamic acid , isomerization , catalysis , redox , derivative (finance) , combinatorial chemistry , medicinal chemistry , organic chemistry , stereochemistry , antioxidant , financial economics , economics
Esculetin ( 1 ) and the novel compounds 5‐chloroesculetin ( 5 ) and 5‐bromoesculetin ( 6 ) were obtained from a light‐induced cyclization of trans ‐caffeic acid ( 3 ) catalyzed by [FeNa(edta)] and/or H 2 SO 4 , HCI, or HBr ( Scheme 1 ). The experimental conditions for trans ‐ cis ‐isomerization of the cinnamic‐acid derivative 3 and subsequent non‐enzymatic cyclization were described. The photoperiod and the presence of air and iron‐chelate catalyst are shown to be important parameters that markedly affect yields. The reactions probably occur by a free‐radical mechanism involving a photo‐initiated one‐electron redox process ( Scheme 2 ).