Photoalkylation/-arylation of ortho-Diketones with Unactivated Organic Halides.

A new method for conducting a reductive alkylation/arylation of 1,2-diketones using visible light and unactivated organic halides is presented in this article. This technique does not require a photocatalyst and employs Et3N, a tertiary amine, as a promoter. This amine aids in generating a ketyl radical and an α-aminoalkyl radical, which engages in a C-X bond activation via a halogen atom transfer process (XAT). This approach's success hinges on utilizing Et3N as the promoter. This article's mild and straightforward protocol allows for significantly expanding organic halide substrates, including primary, secondary, and aromatic organic halides and various functional groups.

Direct Synthesis of Benzo[b]fluorenyl Thiophosphates via Tandem Cyclization of Diynols with (RO)2P(O)SH.

A general and metal-free protocol for the construction of benzo[b]fluorenyl thiophosphates was developed through the cascade cyclization of easily prepared diynols and (RO)2P(O)SH, with water as the only byproduct. The novel transformation involved the allenyl thiophosphate as the key intermediate, followed by Schmittel-type cyclization to achieve the desired products. Notably, (RO)2P(O)SH acted not only as a nucleophile but also as an acid-promoter to initiate the reaction.

Visible-light-driven proton reduction for semi-hydrogenation of alkynes via organophotoredox/manganese dual catalysis.

Described here is a unprecedented organophotoredox/manganese dual catalyzed proton reduction and its application for semi-reduction of alkynes. The catalytic active pre-catalyst [Mn-1] can be feasibly be prepared on gram-scale from Mn(acac)2·2H2O in air. This dual catalytic protocol features noble-metal-free catalysts, simple ligand, and mild conditions. Besides, a unique ortho-halogen and -hydroxyl effect was observed to achieve high Z-stereoselectivity.

Photoredox/nickel dual-catalyzed regioselective alkylation of propargylic carbonates for trisubstituted allenes.

Herein, a highly regioselective alkylation of propargylic carbonates for trisubstituted allenes with alkyl 1,4-dihydropyridine derivatives (1,4-DHPs) is developed via a photoredox/nickel dual-catalyzed process, which represents the first direct approach to access alkylated allene products without alkyl organometallic reagents. This method features a broad substrate scope and mild conditions. A hypothetical mechanism with an alkyl radical and an allenyl Ni(III) species is proposed. Benzylation products were also obtained to be the complement building blocks for the potential synthesis of pharmaceuticals.

Synthesis of Enantiopure Hydrocarbon Cages Based on an Optically Resolved C3-Symmetric Triaminotribenzotriquinacene.

The synthesis of the enantiomerically pure, D3-symmetric covalent hydrocarbon cages (+)-(M,M)-4 and (-)-(P,P)-4 bearing two C3-symmetrically functionalized tribenzobenzotriquinacene (TBTQ) vertices is reported. The enantiomerically pure TBTQ building blocks (+)-(M)-5 and (-)-(P)-5 were prepared via the diastereomeric TBTQ triamides obtained by use of both Boc-d- and Boc-l-phenylglycine as chiral auxiliaries.

Visible-light photoredox-catalyzed C-O bond cleavage of diaryl ethers by acridinium photocatalysts at room temperature.

Cleavage of C-O bonds in lignin can afford the renewable aryl sources for fine chemicals. However, the high bond energies of these C-O bonds, especially the 4-O-5-type diaryl ether C-O bonds (~314 kJ/mol) make the cleavage very challenging. Here, we report visible-light photoredox-catalyzed C-O bond cleavage of diaryl ethers by an acidolysis with an aryl carboxylic acid and a following one-pot hydrolysis. Two molecules of phenols are obtained from one molecule of diaryl ether at room temperature. The aryl carboxylic acid used for the acidolysis can be recovered. The key to success of the acidolysis is merging visible-light photoredox catalysis using an acridinium photocatalyst and Lewis acid catalysis using Cu(TMHD)2. Preliminary mechanistic studies indicate that the catalytic cycle occurs via a rare selective electrophilic attack of the generated aryl carboxylic radical on the electron-rich aryl ring of the diphenyl ether. This transformation is applied to a gram-scale reaction and the model of 4-O-5 lignin linkages.

Visible-Light Photoredox-Catalyzed Decarboxylative Alkylation of Heteroarenes Using Carboxylic Acids with Hydrogen Release.

Herein, we have developed visible-light photoredox-catalyzed decarboxylating carboxylic acids for alkylation of heteroarenes under mild conditions. The transformation occurred smoothly without the requirement of stoichiometric oxidants in the presence of 0.3 equiv of base, which benefited from the release of hydrogen (H2) and carbon dioxide (CO2). Various substrates and functional groups were tolerated. Primary mechanistic studies suggest that an oxidative quenching pathway and a reductive quenching pathway are both possible in the catalytic cycle.

Visible-Light Photoredox-Catalyzed Iminyl Radical Formation by N-H Cleavage with Hydrogen Release and Its Application in Synthesis of Isoquinolines.

An unprecedented visible-light photoredox-catalyzed iminyl radical formation by N-H cleavage with H2 release has been developed. Its application in the synthesis of various isoquinolines and related polyaromatics in high atom economy at ambient temperature by applying a photosensitizer, Acr+-Mes ClO4-, and a new cobalt catalyst, Co(dmgH)2(4-CONMe2Py)Cl is reported. Mechanistic investigations indicated that the generated iminyl radical initiates the cascade C-N/C-C bonds formation and the catalytic cycle occurs by a simultaneous oxidative as well as reductive quenching pathway.

o-Quinones Derived from Tribenzotriquinacenes: Functionalization of Inner Bay Positions and Use for Single-Wing Extensions.

Through a surprisingly nonregioselective oxidation process, the reaction of two analogous 2-hydroxy-substituted tribenzotriquinacenes (TBTQs) 8a/8b by o-iodoxybenzoic acid was found to afford the corresponding Cs- and C1-symmetrical TBTQ-o-quinones 6a/6b and 7a/7b, respectively, in 1:1 ratio and excellent combined yields. This finding represents the first example of direct introduction of a functional group into a sterically hindered, inner bay-positions of a parent TBTQ skeleton. In contrast, the analogous reaction with 1-hydroxy-TBTQ 15 failed to produce the desired o-quinone 7a. After reduction of the quinones 6a and 7a to the corresponding catechols 17 and 23, electrophilic aromatic substitution could also be realized at the activated inner bay-position(s) to afford several tri- and tetrafunctionalized TBTQ compounds 18, 21, and 25. The Cs-symmetrical o-quinone 6a was converted into further single-wing extended derivatives such as TBTQ-based phenazines 27a-f, through condensation reactions, and to benzodioxine derivative 32 by Diels-Alder reaction with tetracyclone. The novel TBTQ-quinones and the corresponding TBTQ-catechols offer a variety of new accesses to single-wing-extended and -functionalized TBTQ derivatives.