Access to Flavones via a Microwave-Assisted, One-Pot Sonogashira−Carbonylation−Annulation Reaction

Abstract

Palladium complexes of 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phenyl-6-phosphaadamantane are shown to be effective catalytic systems facilitating the sequential application of a microwave-assisted Sonogashira and carbonylative annulation reaction for the preparation of substituted flavones.

Microwave irradiation as a sustainable tool for catalytic carbonylation reactions

“…The carbonylation-annulation reaction between ortho-hydroxyl iodobenzene derivative 38 and 1-butine [ 38 ], to afford flavone 39, was performed using bis(dibenzylideneacetone)palladium(0)/1,3,5,7-tetramethyl-2,4,8-trioxa-6-phenyl-6-phosphaadamantane (Pd 2 (dba) 3 /PA-Ph) as catalyst, DBU as base, at low CO pressure The application of MW irradiation for Sonogashira reactions, followed by a aminocarbonylation/cyclization to produce flavones with yields up to 70% (Scheme 9) [38]. As example, the coupling of p-iodotoluene with TMS-acetylene in the presence of Pd 2 (dba) 3 3-Nitro-iodobenzene and benzylamine were selected as model compounds for optimization of 11 C-aminocarbonylation using Pd 2 (π-cinnamyl)Cl 2 -XANTPHOS as catalyst, yielding the corresponding benzylamide with up to 99% (Scheme 10) [39].…”

Microwaves in Heterocyclic Chemistry

“…Microwave-assisted reactions proceeded more smoothly to give higher yields (31-61%) with to those under classical thermal conditions with significant shortening of reaction times (18-50 min instead of 1.5-5 h with thermal heating). A particularly attractive approach to substituted flavones has been realized under microwave irradiation by one-pot Sonogashira-carbonylation-annulation reactions [135]. A series of 3-(1-alkynyl)chromones was used with various acetonitriles to afford functionalized amino-substituted xanthones by a novel base-promoted tandem reaction [136] (Table 16.9).…”

Microwave‐Heated Transition Metal‐Catalyzed Coupling Reactions

“…In 2009, Awuah and Capretta described an elegant one-pot strategy in which a Sonogashira cross-coupling reaction was followed by a desilylationcarbonylative Sonogashira annulation sequence for the synthesis of substituted flavones [146]. A low Pd 2 (dba) 3 loading and 1,3,5,7-tetramethyl-2,4,8-trioxa-6-phenyl -6-phosphaadamantane (PA-Ph) as ligand source were employed in both steps to react suitable aryl halides with trimethylsilylacetylene.…”