Visible-Light-Induced C(sp2)-C(sp3) Cross-Dehydrogenative-Coupling Reaction of N-Heterocycles with N-Alkyl-N-methylanilines under Mild Conditions

Visible-Light-Induced C-H Alkylation of 1,2,4-Triazine-3,5(2H,4H)-diones via Infrequent 1,2-Hydrogen-Atom Transfer

1,2,4-Triazine-3,5(2H,4H)-diones are widely present in various drug molecules and bioactive molecules. A visible-light-driven C-H alkylation of 1,2,4-triazine-3,5(2H,4H)-diones via 1,2-hydrogen-atom transfer (1,2-HAT) of amide radicals is first reported, providing an environmentally friendly and sustainable pathway to enrich the structural and functional diversity of 1,2,4-triazine-3,5(2H,4H)-diones. This novel protocol is characterized by mild and metal-free reaction conditions, an operationally simple method, and good functional group tolerance. To our delight, other heterocycles, such as isoquinoline and coumarin, also undergo alkylation reactions to construct C(sp2)-C(sp3) bonds via infrequent 1,2-HAT under current conditions.

Mn-catalyzed oxo-alkylation of 1,2,4-triazine-3,5(2H,4H)-diones with cyclic alkanols via oxidative cross-dehydrogenative coupling

An efficient and convenient pathway to synthesize diverse 3 or 4-oxo-alkyl substituted 1,2,4-triazine-3,5(2H,4H)-diones has been reported via an atom- and step-economical cross-dehydrogenation coupling strategy with good functional group tolerance and wide substrate scope. The present transformation employs inexpensive manganese salt catalysts and iodobenzene diacetate oxidants at room temperature. The synthetic utility of this pathway is further demonstrated by a gram scale reaction.

Visible Light-Induced C-H Alkylation of Azauracils with N-Hydroxyphthalimide Esters via Catalytic EDA Complex

Herein, we report sodium iodide (NaI)-catalyzed decarboxylative C-H alkylation of azauracils with N-hydroxyphthalimide (NHPI) esters facilitated by visible light activation of catalytic electron donor-acceptor (EDA) complexes. Control experiments and density functional theory calculations suggest that the decarboxylative coupling reaction proceeds via a transiently assembled EDA complex between the NHPI ester and NaI in N,N-dimethylacetamide solvent. This synthetic method efficiently applies to primary, secondary, and tertiary NHPI esters under mild, photocatalyst-free, and redox-neutral conditions, achieving high yields of the desired alkylated azauracils.

Cu(I)-Catalyzed Silylation and Germylation of Azauracils

The current study demonstrates a Cu(I) catalyzed direct C(sp2)-H silylation and germylation of azauracil using triphenylsilane and triphenylgermane. A broad scope, excellent functional group tolerance, and suitability for large-scale reactions are exhibited in this protocol. Moreover, this method can be readily applied to structurally complex bioactive molecules. Experimental results suggest a radical mechanistic pathway for the reaction.

Electrochemical C-H Alkylation of Azauracils Using N-(Acyloxy)phthalimides

We present an electrochemical alkylation of azauracils using N-(acyloxy)phthalimides (NHPI esters) as readily available alkyl radical progenitors under metal- and additive-free conditions. Several azauracils are shown to undergo alkylation with an array of NHPI esters (1°, 2°, 3°, and sterically congested), providing the desired products in good to excellent yields. This operationally simple method is robust, scalable, and suitable for both batch and flow setups.

Photocatalyzed Acylation of Azauracil Derivatives with Aldehydes

A novel approach for the acylation of azauracil derivatives with aldehydes has been developed utilizing sodium decatungstate (NaDT) as a photocatalyst. This method demonstrates broad substrate tolerance and yields moderate to excellent outcomes. Notably, it aligns with green chemistry principles by eliminating oxidants, utilizing eco-friendly energy sources, and offering high scalability and operational simplicity.

Visible-Light-Induced C-H Cyanoalkylation of Azauracils with Cycloketone Oxime Esters via Catalytic EDA Complex

Photoexcitation electron donor-acceptor (EDA) complexes provide an effective approach to produce radicals under mild conditions, while the catalytic version of EDA complex photoactivation remains scarce. Herein, we report a visible-light-induced organophotocatalytic pathway for the cyanoalkylation of azauracils using inexpensive and readily available 1,4-diazabicyclo[2.2.2]octane (DABCO) as a catalytic electron donor. This synthetic method exhibits exceptional compatibility with various functional groups and presents 34 examples in high yields. The efficient cyanoalkylation offers an environmentally friendly and sustainable route toward enhancing the structural and functional diversity of azauracils.

Metal- and Photocatalyst-Free, Visible-Light-Initiated C3 α-Aminomethylation of Quinoxalin-2(1H)-ones via Electron Donor-Acceptor Complexes

We report a metal- and photocatalyst-free C3 α-aminomethylation of quinoxalin-2(1H)-ones with N-alkyl-N-methylanilines. The reaction proceeds through the formation of a photoactivated electron donor-acceptor complex between quinoxalin-2(1H)-ones and N-alkyl-N-methylanilines. The present method provides a mild and environmentally friendly protocol that exhibits good atom economy and excellent functional group tolerance to obtain a library of biologically significant C3 α-aminomethylated quinoxalin-2(1H)-ones in good yields.

Photodecarboxylative C-H Alkylation of Azauracils with N-(Acyloxy)phthalimides

We disclose a transition-metal-free NaI/PPh₃-mediated direct C-H alkylation of azauracils using N-(acyloxy)pthalimides (NHPIs) as readily available alkyl surrogates under visible light irradiation. Detailed mechanistic studies reveal formation of a photoactivated electron donor-acceptor (EDA) complex between NaI/PPh₃, TMEDA, and alkyl NHPI ester and establish the crucial role of TMEDA in increasing the activity of the photoredox system. The reaction demonstrates a broad scope, scalability, and appreciable functional group tolerance. A variety of azauracils are shown to undergo alkylation by primary, secondary, and tertiary NHPI esters under mild conditions, furnishing the desired products in good to excellent yields.

Visible-Light-Induced Oxyalkylation of 1,2,4-Triazine-3,5(2H, 4H)-diones with Ethers via Oxidative Cross-Dehydrogenative Coupling

An efficient and convenient method to synthesize 6-oxyalkylated 1,2,4-triazine-3,5(2H, 4H)-diones has been developed via visible-light-induced cross-dehydrogenative coupling reaction between 1,2,4-triazine-3,5(2H, 4H)-diones and ethers with a wide range of functional group tolerance. The present transformation employs the cheap and low-toxic 2-tert-butylanthraquinone as a metal-free photocatalyst and air as a green oxidant at room temperature. Moreover, this reaction can also be driven by sunlight as a clean energy resource. The synthetic utility of this method is further demonstrated by gram-scale reaction and application in the preparation of key intermediates of bioactive molecules.