Ring opening and recyclization reactions with 3-functionalized chromones: Recent synthetic approaches for five, six and seven membered heterocycles
Al‐Shimaa Badran, Zeinab Hussain, N.S. Abdelshafi, Salah S. Ibrahim, Aya Ahmed, Mohamed Abdel‐Megid, Magdy A. M. Ibrahim
Abstract
Chromones are active substrate for building heterocyclic systems due to the availability of electron deficient γ-pyrone moiety. Substituted chromones are highly valuable intermediates that can be used to construct many types of heterocyclic compounds through γ-pyrone ring opening followed by recyclization (RORC) either with carbonyl function at C-4 position or with functional groups located at C-3 position. 3-Formylchromones are versatile substrates for building five, six and seven membered heterocycles through reaction with 1,2-, 1,3- and 1,4-binucleophiles, respectively. These reactions mainly proceed through nucleophilic condensation with the aldehyde function with subsequent γ-pyrone ring opening via attack at C-2 position. Other 3-functionallized chromones reacted with binucleophilic reagents through nucleophilic attack at C-2 position with subsequence recyclization with carbonyl function at C-4 position or functional groups located at C-3 position. Using several synthetic approaches under different reaction conditions, a diversity of heterocyclic systems such as pyrazoles, isoxazoles, pyridines, pyrimidines, pyrans, diazepines, oxadiazepines and thiadiazepines were efficiently synthesized from 3-functionallized chromones. Collecting and discussion of the chemical transformation of 3-functionalized chromones with nitrogen and carbon nucleophiles is the main goal of the current review; since 2012 till 2024.