title: Cyclization of ortho-hydroxycinnamates to coumarins under mild conditions: A nucleophilic organocatalysis approach.
abstract: (E)-Alkyl ortho-hydroxycinnamates cyclize to coumarins at elevated temperatures of 140-250 °C. We find that the use of tri-n-butylphosphane (20 mol %) as a nucleophilic organocatalyst in MeOH solution allows cyclization to take place under much milder conditions (60-70 °C). Several coumarins were prepared, starting from ortho-hydroxyarylaldehydes, by Wittig reaction with Ph(3)P=CHCO(2)Me to (E)-methyl ortho-hydroxycinnamates, followed by the phosphane catalyzed cyclization.
authors.affiliation: Department Chemie, Technische Universität München, Lichtenbergstr. 4, 85748 Garching, Germany.
authors.forename: Florian
authors.initials: F
authors.lastname: Boeck
authors.forename: Max
authors.initials: M
authors.lastname: Blazejak
authors.forename: Markus R
authors.initials: MR
authors.lastname: Anneser
authors.forename: Lukas
authors.initials: L
authors.lastname: Hintermann