Transition Metal‐Free Oxidative Cross‐Coupling C(sp²)–C(sp³) Bond Formation: Regioselective C‐3 Alkylation of Coumarins with Tertiary Amines

Abstract

A novel transition‐metal‐free regioselective C‐3 alkylation of coumarins was realized under mild reaction conditions. Various coumarins and tertiary amines smoothly underwent direct C(sp2)–C(sp3) bond formation in the presence of (n‐Bu)4NI as the catalyst and t‐BuOOH as the oxidant.magnified image

Acid‐Catalyzed Intramolecular Imination / Nucleophilic Trapping of 4‐Aminobutanal Derivatives: One‐Pot Access to 2‐(Pyrazolyl)pyrrolidines

“…The first one includes the modification of an existing pyrrolidine fragment. Various cross‐coupling reactions of heteroaromatics with appropriately substituted pyrrolidine derivatives, including oxidative and photooxidative ones, are the most often used within this pathway. Synthesis of enantiomerically pure 2‐(hetaryl)pyrrolidines in several cases has also been accomplished by decarboxylative heteroarylation of proline derivatives …”

Visible Light‐Induced Regioselective Decarboxylative Alkylation of the C(sp2)−H Bonds of Non‐Aromatic Heterocycles

“…Indeed, Heck‐type alkylations of non‐aromatic heterocycles are rarely reported (Scheme , eq 1) . Recently, the oxidative alkylation of these heterocycles as an alternative method has been intensely studied via reactive radical intermediates (Scheme , eq 2) . Despite these important advances, current methods suffer from elevated reaction temperatures and the use of strong oxidants.…”

“…Non-aromatic heterocycles, such as coumarins, quinolinones, and quinoxalinones, are a class of significant organic compounds that are found in natural products, pharmaceuticals, and material chemistry. [1] Over the past decade, extensive research efforts have been devoted to methodological studies of the construction [2] and CÀ H functionalization [3][4][5][6][7][8][9][10][11][12][13][14] (e. g., arylation, [3] olefination, [4] phosphorylation, [5] and amination [6] ) of these scaffolds to enhance their properties for further application. Although alkylated non-aromatic heterocycles are valuable in various fields, [1] their direct and general syntheses via C(sp 2 )À H bond alkylation are limited.…”

“…[9] Recently, the oxidative alkylation of these heterocycles as an alternative method has been intensely studied via reactive radical intermediates (Scheme 1, eq 2). [10][11][12][13][14] Despite these important advances, current methods suffer from elevated reaction temperatures and the use of strong oxidants. Due to the common use of peroxides as radical initiators and terminal oxidants, the substrate scope is limited to those with a relatively weak CÀ H bond that can be selectively and homolytically cleaved, such as alkylbenzenes, [10] tertiary amines [11] and (cyclo)alkyl ethers [12] as well as cycloalkanes, [10c,12a,d,e,13] restricting the application of this strategy.…”

“…Initially, the organic and inorganic bases, such as DABCO (triethylenediamine), DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), Et 3 N, TMEDA (N,N,N',N'-tetramethylethylenediamine), and Cs 2 CO 3 , were examined as additives ( Table 1, entries [2][3][4][5][6], and the addition of DABCO provided an excellent yield for 3 aa (85%, Table 1, entry 2). However, the reaction was suppressed by the addition of an acid (i. e., CF 3 COOH and CH 3 COOH), and only a trace amount of 3 aa was observed ( [9][10][11][12]. In the absence of the photocatalyst or light, no desired product was observed ( Table 1, entries 15 and 16).…”