Ring opening and recyclization reactions with 3-functionalized chromones: Recent synthetic approaches for five, six and seven membered heterocycles

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.