PdII-Catalyzed Reaction of Phenols with Propiolic Esters. A Single-Step Synthesis of Coumarins

Abstract

The intermolecular reaction of phenols with propiolic esters in TFA in the presence of a Pd(OAc)2 catalyst, affording coumarin derivatives, is described. An exclusive formation of 5,6,7-trimethoxy-4-phenylcoumarin was observed in the reaction of 3,4,5-trimethoxyphenol and ethyl phenylpropiolate with a catalytic amount of Pd(OAc)2. The reaction in the absence of Pd(OAc)2 did not give any coumarin at all. Coumarin derivatives were obtained in high yields in the cases of electron-rich phenols, such as 3,4-methylenedioxyphenol, 3-methoxyphenol, 2-naphthol, and 3,5-dimethoxyphenol. Furthermore, the reaction of some phenols with various 2-alkynoates or with diethyl acetylenedicarboxylate gave the corresponding coumarins in good-to-high yields.

Trifluoroacetic Acid-Mediated Hydroarylation: Synthesis of Dihydrocoumarins and Dihydroquinolones

“…We began our study by repeating the reported procedure for the hydroarylation of p -methoxycinnamic acid 2a with 3,4,5-trimethoxyphenol 1a in the presence of 1 mol % of Pd(OAc) 2 in 4:1 TFA:CH 2 Cl 2 (Scheme ). 1a,4a Consistent with the literature report, a 96% yield of the dihydrocoumarin derivative 3a was isolated. To determine the background rate of uncatalyzed hydroarylation, we repeated this experiment in the absence of Pd(OAc) 2 .…”

“…Development of catalysts for the hydroarylation of alkynes and olefins by the addition of a C−H bond across a π-bond has received significant recent attention. , These reactions are particularly interesting from the standpoint of green chemistry because hydroarylation exhibits perfect atom economy and relies on the use of simple arene reactants (Scheme ) . Furthermore, the ability to synthesize coumarins and chromenes through hydroarylation of alkynes establishes the synthetic utility of these C−H bond functionalization reactions.

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“…In comparison to the hydroarylation of alkynes, the catalytic addition of arenes to alkenes has received much less attention. Thus, we were intrigued by reports that Pd(OAc) 2 in trifluoroacetic acid (TFA) effected the room temperature hydroarylation of alkenes. , With the goal of investigating possible mechanistic differences between alkyne and olefin hydroarylation, we began examining the intra- and intermolecular hydroarylation of alkenes. In the course of these studies we discovered that, in contrast to literature reports, the hydroarylation of cinnamic acids in trifluoroacetic acid is not palladium catalyzed.…”

Developments in Catalytic Aromatic C-H Transformations: Promising Tools for Organic Synthesis

“…Kitamura et al recently developed a palladium-catalyzed reaction of phenols with propiolic esters to form coumarins (Scheme 28) [65]. The catalytic reaction tolerates a variety of substituents on the phenols as well as on the 2-alkynoate.…”

Σύνθεση Και Μελέτη Πυρανοινδολονών (Πυρρολοκουμαρινών) Και Συμπυκνωμένων Παραγώγων Αυτών Με Πιθανό Βιολογικό Ενδιαφέρον

“…τον Kitamura και τους συνεργάτες τους μελετήθηκε48 η σύνθεση κουμαρινών μέσω διαμοριακής αντίδρασης φαινολών με προπιολικούς εστέρες σε τριφθοροξικό οξύ (TFA), παρουσία καταλυτικής ποσότητας Pd(OAc) 2 (Σχήμα 17). -αλκυνοϊκών εστέρων ο οποίος περιλαμβάνει την προσβολή σε ορθο-θέση της φαινόλης του συμπλόκου Pd(OCOCF 3 ) 2 , και στη συνέχεια, υδροαρυλίωση του αλκυνοϊκού εστέρα 61 και, τέλος, κυκλοποίηση (ενδομοριακή μετεστεροποίηση).…”