Copper-catalyzed decarboxylative and oxidative decarbonylative cross-coupling between cinnamic acids and aliphatic aldehydes

Abstract

A convenient copper-catalyzed decarboxylative and oxidative decarbonylative cross-coupling of cinnamic acids with aliphatic aldehydes was achieved, which provides a useful strategy of C(sp3)–C(sp2) bonds construction for the synthesis of alkyl-substituted E-alkenes.

Metal‐Free Synthesis of 3,4‐Dihydroquinolin‐2(1H)‐Ones via Cascade Oxidative Decarbonylative Radical Alkylation/Cyclization of Cinnamamides with Aliphatic Aldehydes

“…In accordance with the experimental results and literatures precedent, a possible mechanism was postulated in Scheme . Firstly, tert ‐butoxyl radical was formed by homolysis of DTBP, and the acyl radical A was generated by tert ‐butoxyl radical removing the aldehyde hydrogen atom.…”

“…It is noteworthy that, the primary carbon radicals obtained from linear aliphatic aldehydes, such as 2‐phenylethanal ( 2 f ), 3‐phenylpropanal ( 2 g ), butyraldehyde ( 2 h ) and hexanal ( 2 i ), could be converted to the corresponding linear alkyl‐substituted cycloadducts ( 4 f – 4 i ) in moderate yields successfully. Interestingly, no regio‐isomer was monitored owing to the radical rearrangement for the aliphatic aldehydes studied …”

“…As we know, easily available aliphatic aldehydes can also behave as an alkyl radical source . Recently, we just reported the addition of a variety of alkyl radicals generated from aliphatic aldehydes to the double bond of cinnamic acids . As the extension of our previous work, we presented here a direct and efficient approach to synthesis of valuable alkyl‐substituted 3,4‐dihydroquinolin‐2(1 H )‐ones through cascade oxidative decarbonylative radical alkylation/cyclization procedure under metal‐free conditions (Scheme e).…”

Recent Advances of Cinnamic Acids in Organic Synthesis

“…, acyl and ketonic radicals were reported. Toluene, boron reagents, aldehydes, acids, amides, ketones, ethers, alcohols, epoxides, nitriles were able to function as radical precursors.…”

“…As benzyl‐type radicals could trigger radical addition/ decarboxylation of cinnamic acids, different leaving groups (H, Bpin, CHO) drawing researchers’ attentions. DTBP was frequently used in this oxidative C−H activation and radical formation.…”