Metal-free synthesis of carbamoylated dihydroquinolinones via cascade radical annulation of cinnamamides with oxamic acids

We report a metal-free procedure for the sustainable synthesis of carbamoylated dihydroquinolinones via tandem addition-cyclization of carbamoyl radicals to cinnamamides. Readily accessible, non-toxic and inexpensive oxamic acids are used as carbamoyl radical precursors. This highly straightforward method provides a mild and environmentally friendly route showing good atom economy and excellent functional group tolerance to obtain diverse medicinally important carbamoylated dihydroquinolinones in one pot. The cascade cyclization is also modular and step-economical with a wide substrate scope and the products were obtained in good to excellent yields. Additionally, the tolerance to air and water, operational simplicity, low cost and scalability enhance the practical value of the proposed synthetic strategy. Preliminary mechanistic studies reveal that cheap and environment-friendly ammonium persulfate acts as a radical initiator in the cascade process and generates carbamoyl radicals from oxamic acids. The synthetic utility of this method is further demonstrated by late stage functionalization of drug molecules with good yields.

Visible-Light-Induced Metal- and Photocatalyst-Free Radical Cascade Cyclization of Cinnamamides for Synthesis of Functionalized Dihydroquinolinones

Visible-light-promoted metal- and photocatalyst-free radical cascade cyclization of cinnamamides with α-oxocarboxylic acids is described for sustainable synthesis of diverse pharmaceutically important dihydroquinolinone scaffolds in one pot under mild conditions. The decarboxylative cascade cyclization proceeded efficiently at room temperature without the need for expensive photocatalysts such as Ir or Ru complexes, which indicates the practicability and environmentally benign nature of this protocol. Preliminary mechanistic studies reveal that the blue LED irradiation efficiently cleaves the I-O bond of the hypervalent iodine reagent PhI(O₂CCOAr)₂ formed through ligand exchange between iodobenzene diacetate and arylglyoxylic acid to initiate the cascade reaction. The synthetic value of this operationally simple and energy-efficient method is further demonstrated by late-stage functionalization of drug molecules in excellent yields.

Iron-catalyzed decarboxylative and oxidative decarbonylative cross-coupling: a new strategy for the synthesis of monofluoroalkenes

Herein, an iron(ii)-catalyzed decarboxylative and oxidative decarbonylative cross-coupling of α-fluoro cinnamic acids with aliphatic aldehydes is presented.

Dibromination of Cinnamamides with CBr4 Under Mild Conditions

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A novel, mild and efficient protocol to synthesize dibrominated propanamides has been developed. The presented methodology provides several merits, such as easy-to-handle and stable brominated substrate, catalyst-free, additive free and facile experimental operation. The preliminary mechanism study indicated that a free radical pathway might be involved in the presented reaction.

Recent advances in decarbonylative annulation reactions

In recent years, decarbonylative annulation reactions have emerged as one of the most efficient routes to construct a variety of important carbocyclic and heterocyclic scaffolds. The main advantages of this type of reaction are, first, the carbonyl compounds are used as the starting materials which are abundant in nature and second, the major by-product of this reaction is carbon monoxide. In the last two decades, various intramolecular and intermolecular decarbonylative annulation reactions have been performed using carbonyl compounds and alkenes/alkynes/arenes/isocyanates etc. as the annulation partners. These reactions are typically performed either in the presence of or in the absence of a metal catalyst. However, these reactions are still in their infancy as a very little progress has been achieved in these reactions. Through this review article, it is attempted to highlight the recent developments on various decarbonylative annulation reactions which ultimately lead to the formation of important structural moieties.