Cyclization of 2′-hydroxychalcones to flavones using ammonium iodide as an iodine source: An eco-friendly approach

Abstract

Ammonium iodide on exposure to air decomposes to ammonia and iodine. The in situ generated iodine was used for the cyclization of 2′-hydroxychalcones to the corresponding flavones under solvent-free conditions in good to excellent yields. This method could serve as an attractive alternative to the existing methods for synthesis of flavones and the use of toxic molecular iodine is avoided.

Recent advances in the synthesis of 4H-chromen-4-ones (2012 − 2021)

“…The in situ generated iodine was used for the cyclization of 2 0 -hydroxychalcones to 2-aryl-4H-chromen-4-ones, under solvent-free conditions (Scheme 8). 99 2-(2-Chloroquinolin-3-yl)-4H-chromen-4-ones were readily obtained from iodine-alumina catalyzed cyclization reaction of 1-(2-hydroxyaryl)-3-(2-chloroquinolin-3-yl)prop-2-en-1-ones under microwave irradiation (400 W) for 3 to 5 min, in excellent yields. 100…”

Structural derivatization strategies of natural phenols by semi-synthesis and total-synthesis

“…Triethylene Glycol (TEG) was a common alternative solvent, might leading to higher yield for specific flavones [168,169]. However, excess iodine and reaction time will give rise to the formation of 3-iodoflavones [170], while novel iodine sources such as iodine monochloride [171] and ammonium iodide [172] have been developed to solve this problem. In a water-mediated phosphorylative cyclodehydrogenation, flavones and flavanones can be synthesized in the same condition with the product type controlled by dosage of reagent [173].…”

An efficient one pot I2/DMSO mediated synthesis and molecular modeling of novel fused pyrimidine‐chromone hybrids bearing potential antibacterial and antifungal pharmacophores sites

“…Many synthetic methodologies were reported to synthesize chromones and flavones; like base catalyzed cyclization of alkynyl ketones or Pd activated cyclo‐carbonylation of o‐Iodophenols with terminal acetylenes using CO [33–36]. Many reagents that have been reported in the literature for the oxidation of chalcones to obtain chromones are SeO 2 ‐pentan‐1‐ol, Pd‐C/vacuum, SeO 2 ‐DMSO, DDQ‐dioxane, t‐BuOK, NaIO 4 ‐DMSO, I 2 ‐DMSO, nickel peroxide‐dioxane, H 2 O 2 ‐NaOH, Dowex‐2‐propanol, SeO 2 ‐dioxane, SeO 2 ‐isoamyl alcohol, Br 2 ‐NaOH, Tl(NO 3 ) 3 .3H 2 O, and I 2 ‐triethylene glycol [47]. Although the previous methods and reagents are useful, still they suffer from various drawbacks like use of a harsh catalytic agents, least cost effectiveness, low yields, high temperature, longer reaction time, and limited number of commercially available starting materials.…”