Practical and Green Protocol for the Synthesis of Substituted 4H‐Chromenes Using Room Temperature Ionic Liquid Choline Chloride–Urea

Abstract

An efficient and convenient synthesis of substituted 4H‐chromenes is described using room temperature ionic liquid (RTIL) choline chloride–urea in one pot under solvent free conditions. Three‐component Knoevenagel condensation of an aromatic aldehyde, with an active methylene compound, and a cyclohexane dione is reported. This new approach has advantage of excellent yields (82–96%), clean reaction, and short reaction time (15–30 min) at room temperature.

Contemporary development in sequential Knoevenagel, Michael addition multicomponent reaction for the synthesis of 4-Aryl-5-oxo-5H-indeno[1,2-b]pyridine-3-carbonitrile

“…acid [69,70], base [71,72], microwave synthesis [58], ionic liquid [73,74], etc., are cited in literature, but they have their own merits and demerits. It has been evidenced that in most of the cases, the synthesis of the N-containing skeleton is carried out by using ammonium salts as an N-source, but in the absence of an ammonium salt, aromatic aldehyde, malononitrile, and 1,3-diketone react to give a pyran derivative [75][76][77]. There are similar reactions observed in the literature [78][79][80] with its own merits and demerits.…”

“…Astonishingly, we obtained again the corresponding pyridine derivative 4a (Table 1, entry 4n) instead of the expected pyran. However, a literature study [75][76][77] reveals that the one-pot domino reaction between aromatic aldehyde, malononitrile, and 1,3-dicarbonyl compounds like cyclohexane-1,3-dione [75] or dimedone [76,77] exclusively give the corresponding pyran. Thus, we performed a one-pot domino reaction (Scheme 2) between 4-(dimethylamino)benzaldehyde (1), malononitrile (2), and 1,3-indandione (3) in which, as expected, we obtained the pyran 2-amino-4-[4-(dimethylamino)phenyl]-5-oxo-4,5-dihydroindeno[1,2-b]pyran-3-carbonitrile (6a), which confirmed by the spectroscopic techniques.…”

“…1,3-indandione 3 ? malononitrile 2 à Domino addition: All components are initially added (N,N dimethyl benzaldehyde 1, malononitrile 2, 1,3-indandione 3) mentioned for the formation of pyran derivatives [75][76][77], we focused our efforts on the sequential studies consisting of the alteration in the addition sequence of the reactants. We tried the same reaction in an alternating way, e.g.…”

Deep Eutectic Solvents in Organic Synthesis

“…In this case, they reported clean, high-yielding reactions at room temperature in 30 minutes. [43] (Scheme 16) Considering the very high viscosity of CC/U at room temperature, it is unclear how useful such reaction conditions would be, and the difference in reported results between the two groups is a concern.…”

Ferrite-supported glutathione: an efficient, green nano-organocatalyst for the synthesis of pyran derivatives

“…[1][2] They also exhibit wide-range of biological and pharmaceutical uses such as anticancer, 3 antibacterial, 4-6 antimicrobial 7 and antiallergic. 24 Reactions in glycerol 25 or choline chloride-urea 26 has also been reported. 1).…”