Catalyst- and solvent-free C_sp2–H functionalization of 4-hydroxycoumarins via C-3 dehydrogenative aza-coupling under ball-milling

Abstract

A one-pot procedure for the synthesis of biologically relevant coumarin-hydrazones by a three-component reaction between 4-hydrocoumarins, primary aromatic amines and tert-butyl nitrite under ball-milling in the absence of any catalyst/additive...

Photo- and Electrochemical Organic Transformations Involving Radical Pathway: A Retrospection of Our Green-Chemistry-Inspired Synthetic Endeavours

“…20 We developed, for the first time, a visible light (white LEDs)-induced straightforward and efficient protocol for the synthesis of 2-hydroxybenzofuran-3(2 H )-ones containing either an ester or an amide functionality at the same position, thereby accessing a new series of pharmaceutically interesting functionalized 2-hydroxy-3-oxo-2,3-dihydrobenzofuran-2-carboxamides 26 and 2-hydroxy-3-oxo-2,3-dihydrobenzofuran-2-carboxylates 28 from the corresponding reaction between 4-hydroxycoumarins 21 and amines 25 in 1,4-dioxane or between 4-hydroxycoumarins 21 and alcohols 27 in the absence of any added solvent, making good use of singlet oxygen in the presence of rose bengal as the photosensitizer at ambient temperature (25–28 °C) (Scheme 13 ). 21 The carboxamides 26 were isolated in moderate to good yields, ranging from 51 to 86%, within 0.8 to 3.5 hours, whereas the carboxylates 28 were obtained in yields of 64 to 88% within 4 to 20 hours. The notable advantages of this photochemical transformation of a 4-hydroxy-α-benzopyrone motif into a 2-hydroxy-3-oxo-2,3-dihydrobenzofuran-2-carboxamide/carboxylate scaffold are its use of commercially available low-cost starting materials, a low-energy visible-light source, and a cheap and ecofriendly photosensitizer, along with its broad substrate scope, insertion of molecular oxygen, metal-free synthesis, good to excellent yields, and energy efficiency.…”

Mechanochemical-assisted decarboxylative sulfonylation of α,β-unsaturated carboxylic acids with sodium sulfinate salts

“…It offers a new opportunity for synthesizing organic compounds with solvent-free organic mechanochemical reactions and unlocks new routes towards numerous compounds that are not attainable by other conventional methods. 9 In continuation of our interest in sustainable, green, and novel synthetic methodologies, 10 we hereby report an unprecedented mechanochemical-assisted decarboxylative sulfonylation of α,β-unsaturated carboxylic acids with sodium sulfinates using only potassium iodide as an activator with water ( η = 0.32 μL mg −1 ) as the liquid-assisted grinding additive (LAG) 11 at ambient temperature under ball milling in 10 min. The method works equally well on alkyl and aryl sulfinates at room temperature without needing any metal catalyst, oxidant, base, or inert environment.…”

Visible light mediated organocatalytic dehydrogenative aza-coupling of 1,3-diones using aryldiazonium salts

“…However, this method is limited to the diazenylation of 4-hydroxycoumarin derivatives. 18 In this regard, the advancement of the synthesis of diazenyl compound is still a challenging area for chemists which demand cheap and efficient synthetic techniques. Compared to aryl diazenyl compounds, the alkyl diazenyl compounds are least tolerant and unstable towards functional groups.…”