4‐Hydroxycoumarin: A Versatile Substrate for Transition‐metal‐free Multicomponent Synthesis of Bioactive Heterocycles

Abstract

One-pot multi-component reactions especially under transition-metal-free catalysis served as an efficient, and environmentally friendly method for the construction of value-added compounds. Their importance in organic synthesis has drastically increased due to their operational simplicity, cost-effectiveness, step-and pot-economic nature. On the other hand, the molecular hybridization concept has recently emerged as a key fascinating area in medicinal and organic chemistry for the design of new drugs. Owing to the widespread occurrence in natural products, and pharmaceutical agents, the incorporation of another heterocycle either as substituents or as a fused material into 4-hydroxycoumarin moiety offers new opportunities for the broad application of the targeted coumarin-heterocycles into many branches of chemistry. Considering the importance of both the topics, here we have reviewed the developments achieved in the synthesis of diverse medicinally privileged oxygen, and nitrogen-containing heterocycles as well as spiro-heterocycles either linked or fused with coumarin moiety by using readily accessible 4-hydroxycoumarin as the starting material via one-pot multi-component reaction under transition-metalfree conditions.[a] B. Borah, K.

Ultrasound-assisted transition-metal-free catalysis: a sustainable route towards the synthesis of bioactive heterocycles

“…The synthesis of these compounds where several heterocycles are combined in such a way that leads to the formation of new single molecules from easily available simple starting materials has recently received considerable attention from chemists and pharmacologists for the outstanding properties of the targeted compounds. [180][181][182] The development in this regard realizes the outstanding contribution of Seydimemet et al to the expedient synthesis of a plethora of coumarin-containing pyrano[2,3-c]pyrazoles by introducing the sonochemical activation strategy under organocatalytic conditions (Scheme 37). 183 Under the inuence of 10 mol% of L-proline, the one-pot domino reaction of bketoesters 132 with phenylhydrazine 133, aromatic aldehydes 5, and active methylene 96 in ethanol was carried out in sonication, which provided the respective products 134 in 78-90% yield aer 50 minutes.…”

“…The synthesis of these compounds where several heterocycles are combined in such a way that leads to the formation of new single molecules from easily available simple starting materials has recently received considerable attention from chemists and pharmacologists for the outstanding properties of the targeted compounds. 180–182…”

Sonochemistry in an organocatalytic domino reaction: an expedient multicomponent access to structurally functionalized dihydropyrano[3,2-b]pyrans, spiro-pyrano[3,2-b]pyrans, and spiro-indenoquinoxaline-pyranopyrans under ambient conditions

“…But, again the occurrence of transition-metal-catalyst(s) in chemical processes even at the lowest level often triggers an undesirable impact on the greenness or sustainability of the transformation. 19 Notwithstanding, transition metal catalyst(s) has been successfully employed in the synthesis of valuable structural building blocks; 20 their occurrences in a chemical process is associated with limitations because of their highly toxic nature, and high cost involved in the preparation of transition metal catalyst alongside the requirement of non-commercial supporting ligands for catalyst preparation. Besides these, the elimination of transition-metal-catalyst(s) from chemical transformation which is predominantly required in the pharmaceutical industry is extremely challenging and often results in contamination of the target compounds.…”

Graphene Oxide Catalyzed Synthesis of Fused Chromeno Spiro Pyrrolidine Oxindoles via Tandem Decarboxylation and 1,3-Dipolar Cycloaddition

“…An important aspect that further establishes the importance of 1,3-DCR is the placement of the ylide dipole and alkene or alkyne dipolarophile within the same molecule, which can provide direct access to polycyclic compounds with extensive complexity and interesting architecture ( Padwa and Pearson, 2003 ; Borah et al, 2021a ; Borah et al, 2021b ; Borah et al, 2021b ). Various methods for cycloaddition reactions involve the formation of highly reactive azomethine ylides and the addition of suitable dipolarophiles; the success of this setup is often described in the synthesis of pyrrolidine and pyrrole containing natural products and medicinally important synthetic targets ( Namboothiri and Hassner, 2001 ) Figure 1 .…”