Intramolecular Oxygen Transfer from Nitro Groups to C⋮C Bonds Mediated by Iridium Hydrides

Sequential Catalytic Annulations: Divergent Synthesis of Heterocycles through a Radical [1,4]-Oxygen Shift

A radical [1,4]-oxygen-atom transfer has been realized by the reaction of linear alkyne-tethered ketoximes and ethynylbenziodoxolones (EBX) under sequential catalytic conditions. Mechanism studies indicate that the O atom transfer experiences a cascade O atom radical cyclization/alkynylation/N-O bond photocleavage and subsequent N,O-diradical rearrangement. By the diversification of catalytic sequences, a series of structurally important 3H-pyrrol-3-ones and chlorinated furo[3,2-b]pyrroles are divergently synthesized along with an O atom shift under the catalysis of Cu/Ir photosensitization and Cu/Ir photosensitization/AlCl₃, respectively.

Intermolecular Interception of α-Oxo Gold Carbenes of Nitroalkyne Cycloisomerization with 1,2-Benzo[d]isoxazole: Synthesis of Functionalized Quinazoline 1-Oxides

The known nitrogen-transfer reagent 1,2-benzo[d]isoxazole has been used to trap the postulated α-oxo gold carbene intermediate involved in the [Au]-catalyzed internal redox process of 2-alkynylnitrobenzenes. This process led us to develop a general convergent method for the synthesis of highly functionalized quinazoline 1-oxides.

Gold-Catalyzed Complementary Nitroalkyne Internal Redox Process: A DFT Study

Gold-catalysis, in this century, is one of the most emerging and promising new areas of research in organic synthesis. During the last two decades, a wide range of distinct synthetic methodologies have been unveiled employing homogeneous gold catalysis and aptly applied in the synthesis of numerous natural products and biologically active molecules. Among these, the reactions involving α-oxo gold carbene/α-imino gold carbene intermediates are of contemporary interest, in view of their synthetic potential and also due to the need to understand the bonding involved in these complexes. In this manuscript, we document the theoretical investigations on the regio-selectivity dependence of substitution on the gold-catalyzed cycloisomerization of o-nitroarylalkyne derivatives. We have also studied the relative stabilities of α-oxo gold carbene intermediates.

TfOH-Promoted Decyanative Cyclization toward the Synthesis of 2,1-Benzisoxazoles

A novel solvent-free, TfOH-promoted decyanative cyclization approach for the synthesis of 2,1-benzisoxazoles has been developed. The reactions are complete instantly at room temperature and result in the formation of the desired 2,1-benzisoxazoles in a 34-97% isolated yield.

Metal-free tandem reactions of 2-iodoaryl ynones with sodium azide for the synthesis of benzoisoxazole containing 1,2,3-triazoles

A metal-free approach has been developed for the synthesis of benzo[c]isoxazole (anthranils) containing 1,2,3-triazoles. The reaction proceeded efficiently through a [3 + 2] azide-alkyne cycloaddition, SNAr azidation and denitrogenative cyclization sequence. The metal-free protocol enabled effective construction of one N-O and three C-N bonds in one pot. In addition, the synthetic utility of the current methodology was further demonstrated by late stage modification of the obtained products.

Gold(i)-catalyzed redox transformation of o-nitroalkynes with indoles for the synthesis of 2,3′-biindole derivatives

A gold(i)-catalyzed cascade reaction of o-nitroalkynes with indoles has been reported for the rapid assembly of 2-indolyl indolone N-oxides, which exhibit high anticancer potency against SCLC cells.

Synthesis of a dinuclear europium(iii) complex through deprotonation and oxygen-atom transfer of trimethylamine N-oxide

A dinuclear europium complex was synthesized via unprecedented deprotonation and oxygen-atom transfer of Me₃NO.

Protonated N-Alkyl-2-nitroanilines Undergo Intramolecular Oxidation of the Alkyl Chain upon Collisional Activation

The collisional activation of protonated N-propyl-2-nitroaniline obtained by electrospray ionization shows two major competitive dissociation pathways: the elimination of the elements of propionic acid, [M + H - C₃H₆O₂]⁺ to give an m/z 107 ion, and of the elements of ethanol, [M + H - C₂H₆O]⁺ to give an m/z 135 ion. The mechanistic study reported here addresses these unusual fragmentations to reveal that both occur via a common intermediate formed by the transfer of an oxygen atom from the nitro group to the first carbon atom of the propyl group, allowing elimination of propionic acid and (H₂O + ethene), respectively. The corresponding loss of CH₄O does not occur when the propyl group is replaced by an ethyl group, but elimination of the elements of propanol does occur when propyl is replaced by a butyl group. Further, the product ions of m/z 107 and 135 are also formed when the propyl chain is replaced with a hexyl group.

Silver- versus gold-catalyzed sequential oxidative cyclization of unprotected 2-alkynylanilines with oxone

Divergent catalytic activity of gold and silver complexes towards domino oxidative cyclization reactions of unprotected 2-alkynylanilines.

Rh(iii)-catalyzed chemoselective C–H functionalizations of tertiary aniline N-oxides with alkynes

Two novel Rh(iii)-catalyzed chemoselective functionalizations of tertiary aniline N-oxides with alkynes, including annulation via the sequential C(sp²)–H and C(sp³)–N activation and an O-atom transfer (OAT) process, have been described.

O-Transfer-facilitated cyclizations of propargylamides with TMSN3: selective synthesis of tetrazoles and dihydroimidazoles

Herein, we disclose the O-transfer-facilitated cyclizations of propargylamides with TMSN₃ to selectively afford functionalized tetrazoles and diiodomethylated dihydroimidazoles.

Catalyst-dependent divergent synthesis of pyrroles from 3-alkynyl imine derivatives: a noncarbonylative and carbonylative approach

A novel Ru(0)- and Rh(I)-catalyzed noncarbonylative and carbonylative cycloisomerization of readily available 3-alkynyl imine derivatives has been developed to provide 3,4-fused or nonfused pyrrole derivatives efficiently in moderate to excellent yields. The key steps involve the formation of a ruthenium carbenoid intermediate or a rhodacycle intermediate, respectively. In these reactions, CO can serve as a ligand or a reagent.

Synthesis of α-diketones from alkylaryl- and diarylalkynes using mercuric salts

Both alkylarylalkynes and diarylalkynes 1 are converted into the α-diketones 2 in good yield by the use of mercuric salts, e.g., mercuric nitrate hydrate or mercuric triflate, in the presence of water. Other mercuric salts, e.g., sulfate, chloride, acetate, or trifluoroacetate, do not provide the diketone product. A possible mechanism is proposed.

Synthesis, characterization, and X-ray structures of three iridium(III)-hydrido-cyclometallated-imine complexes, including the first reported hydrido-(η1-imine)-Ir complex

Reactions of cis,trans,cis-[Ir(H)2(PPh3)2(solv)2]PF6 (solv = MeOH or Me2CO) with the imines HN=CPh2, (o-HOC6H4)C(Me)=NCH2Ph, and PhC(H)=N(p-F-C6H4) in MeOH or acetone under Ar give the complexes [IrH{NH=C(Ph)(o-C6H4)}(NH=CPh2)(PPh3)2]PF6 (3), [IrH{PhCH2N=C(Me)(o-C6H3OH)}(solv)(PPh3)2]PF6, where solv = MeOH (4) or Me2CO (4a), and [IrH{N(p-F-C6H4)=CH(o-C6H4)}(Me2CO)(PPh3)2]PF6 (5a), which have been isolated and characterized. The imine (C6F5)C(H)=NPh is unreactive toward the Ir precursors. The X-ray structures of 3, 4·2MeOH, and 5a·1/2Me2CO show an η2-N,C-imine moiety coordinated via the N atom and an orthometallated-C atom. Complex 3, which contains both an orthometallated imine and an η1-imine, is the first structurally characterized hydrido-(η1-imine)-Ir complex. Comparisons are made with data for the corresponding Rh systems.Key words: iridium, hydride complexes, imines, fluoroimines, phosphine complexes, orthometallation, crystallography, NMR spectroscopy.

Intramolecular alkyne hydroalkoxylation and hydroamination catalyzed by iridium hydrides

[reaction: see text] Iridium(III) hydrides prove to be air-stable active catalysts for intramolecular hydroalkoxylation and hydroamination of internal alkynes with proximate nucleophiles. The cyclization follows highly selective 6-endo-dig regiochemistry when regioselectivity is an issue.