Metal-free methodology for the preparation of sterically hindered alkynoylphenols and its application to the synthesis of flavones and aurones

Novel Synthesis of Aurones by 2‐PyONa‐catalyzed Regioselective Cyclization of o‐(Alkynon‐1‐yl)phenols

“…However, the cyclization of o ‐(alkynon‐1‐yl)phenols using K 2 CO 3 or NaOEt was problematic because it provided a mixture of aurones and flavones by 5‐ exo and 6‐ endo attack, respectively . Recently, the use of Lewis bases such as a catalytic PBu 3 and 3 equiv of Cs 2 CO 3 on the 5‐ exo cyclization of o ‐(alkynon‐1‐yl)phenols afforded aurones together with trace amounts of flavones.…”

Tandem Reactions of Ynones: via Conjugate Addition of Nitrogen‐, Carbon‐, Oxygen‐, Boron‐, Silicon‐, Phosphorus‐, and Sulfur‐Containing Nucleophiles

“…Bolshan et al –. developed a metal‐free methodology to prepare flavones 86.1 and aurones 86.2 from sterically hindered alkynoylphenols.…”

Solvent‐Switchable Regioselective Synthesis of Aurones and Flavones Using Palladium‐Supported Amine‐Functionalized Montmorillonite as a Heterogeneous Catalyst

“…However, the use of strong acidic or basic conditions, high temperature, long reaction times, poor functional‐group tolerance, and low yield confines its synthetic utility . The regioselective cyclization of the enone system is one of the prominent methods for the preparation of this type of heterocyclic scaffold …”

“…[14][15][16][17] The regioselective cyclization of the enone system is one of the prominentm ethods for the preparation of this type of heterocyclic scaffold. [18][19][20][21] The transition-metal-catalyzed carbonylation reaction is an attractive method for the construction of various heterocyclic scaffolds as it utilizes CO gas as an inexpensive C 1 source. [22][23][24][25][26][27] In this regard, the Pd-catalyzed carbonylative cyclization of 2-iodophenolsw ith terminal alkynes is as ap rominentm ethod for the synthesis of flavones and aurones.…”