Synthesis of heterocycles via electrophilic cyclization of alkynes containing heteroatom

On water: silver-catalyzed domino approach for the synthesis of benzoxazine/oxazine-fused isoquinolines and naphthyridines from o-alkynyl aldehydes

An operationally simple domino approach for the silver-catalyzed synthesis of oxazine/benzoxazine-fused isoquinolines 5a-q and naphthyridines 6a-v by the reaction of o-alkynyl aldehydes 3a-aa with amines having embedded nucleophiles 4a-d under mild reaction condition in water is described. The reaction shows selective C-N bond formation on the more electrophilic alkynyl carbon resulting in the formation of 6-endo-dig cyclized product. The competitive experiments show the viability of an intramolecular nucleophilic attack over an intermolecular attack of the external nucleophile. This methodology accommodates wide functional group variation, which proves to be useful for structural and biological assessment.

Solution-phase parallel synthesis of a multisubstituted cyclic imidate library

The solution-phase parallel synthesis of a diverse 71-member library of multisubstituted cyclic imidates is described. The key intermediates, 3-iodomethylene-containing cyclic imidates, are readily prepared in good to excellent yields by the palladium/copper-catalyzed cross-coupling of various o-iodobenzamides and terminal alkynes, followed by electrophilic cyclization with I2. These cyclic imidates were further functionalized by palladium-catalyzed Suzuki-Miyaura, Sonogashira, carbonylative amidation, and Heck chemistry using sublibraries of commercially available building blocks.

Scaffold-divergent synthesis of ring-fused indoles, quinolines, and quinolones via iodonium-induced reaction cascades

N-(2-Iodophenyl)imines A are readily formed from Schiff's base condensation of 2-iodoanilines with carbonyls and ketals. These imines provide useful substrates in scaffold-divergent synthesis through the attachment of an alkyne (Songashira coupling or acyl substitution of a Weinreb amide) followed by an iodonium-induced reaction cascade to give ring-fused indoles B, quinolines C, or quinolones D depending on the reaction conditions employed.

The nature of the interaction of dimethylselenide with IIIA group element compounds

The first systematic theoretical study of the nature of intermolecular bonding of dimethylselenide as donor and IIIA group element halides as acceptors was made with the help of the approach of Quantum Theory of Atoms in Molecules. Density Functional Theory with "old" Sapporo triple-ζ basis sets was used to calculate geometry, thermodynamics, and wave function of Me2Se···AX3 complexes. The analysis of the electron density distribution and the Laplacian of the electron density allowed us to reveal and explain the tendencies in the influence of the central atom (A = B, Al, Ga, In) and halogen (X = F, Cl, Br, I) on the nature of Se···A bonding. Significant changes in properties of the selenium lone pair upon complexation were described by means of the analysis of the Laplacian of the charge density. Charge transfer characteristics and the contributions to it from electron localization and delocalization were analyzed in terms of localization and delocalization indexes. Common features of the complexation and differences in the nature of bonding were revealed. Performed analysis evidenced that gallium and indium halide complexes can be attributed to charge transfer-driven complexes; aluminum halides complexes seem to be mainly of an electrostatic nature. The nature of bonding in different boron halides essentially varies; these complexes are stabilized mainly by covalent Se···B interaction. In all the complexes under study covalence of the Se···A interaction is rather high.

Skeletal diversification via heteroatom linkage control: preparation of bicyclic and spirocyclic scaffolds from N-substituted homopropargyl alcohols

The discovery and application of a new branching pathway synthesis strategy that rapidly produces skeletally diverse scaffolds is described. Two different scaffold types, one a bicyclic iodo-vinylidene tertiary amine/tertiary alcohol and the other, a spirocyclic 3-furanone, are each obtained using a two-step sequence featuring a common first step. Both scaffold types lead to intermediates that can be orthogonally diversified using the same final components. One of the scaffold types was obtained in sufficiently high yield that it was immediately used to produce a 97-compound library.

Metal-free reactions of alkynes via electrophilic iodocarbocyclizations

Despite attracting tremendous interest over the last few decades, the field of electrophilic cyclizations is still continuously and rapidly developing. Particularly, metal-free reactions that involve the activation of an alkyne using electrophilic halogen sources are powerful tools in the repertoire of synthetic chemists. This brief overview highlights recent progress in C-C bond-forming halocyclizations allowing for the reaction of alkynes with carbon-nucleophiles. Primarily guided by the type of carbon nucleophile, methods are categorized as the addition of arene, malonate, and olefin nucleophiles.

Iodide-catalyzed halocyclization/cycloaddition/elimination cascade reaction

An iodocyclization reaction of o-alkynylphenyl carboxaldehydes is reported that is truly catalytic with respect to the electrophilic iodine source. With a combination of tetrabutylammonium iodide (TBAI), Oxone as non-nucleophilic and easy to handle co-oxidant, and fluorinated protic solvents, highly substituted 1-naphthalenones could be prepared in high yields of up to 91%.

Silver(I)-catalyzed addition-cyclization of alkyne-functionalized azomethines

AgOTf can catalyze an addition-cyclization tandem between alkyne-azomethine and a nucleophile such as ketone, nitroalkane, water, and terminal alkyne to give a polycyclic amide via six-exo-trig selectivity.

Development of a gold-multifaceted catalysis approach to the synthesis of highly substituted pyrroles: mechanistic insights via Huisgen cycloaddition studies

A novel gold-catalyzed method for the regioselective synthesis of highly substituted pyrroles directly from oximes and alkynes was developed via independent optimization of two key steps of the process. Importantly, a cationic gold(I) species was shown to activate multiple steps along the reaction pathway and therefore act as a multifaceted catalyst. Initial gold-promoted addition of the oxime oxygen to the activated alkyne afforded the O-vinyloxime in situ. The O-vinyloxime was subsequently transformed into the pyrrole via a gold-catalyzed tautomerization, [3,3]-sigmatropic rearrangement, and cyclodehydration process. Notably, this method provides a functional group handle in the form of an ester at the 3/4-position for further exploitation. The proposed mechanistic pathway is supported by a novel application of the Huisgen cycloaddition click reaction, which was used to probe the relative stability of substituted O-vinyloximes. The intermediacy of N-alkenylhydroxylamine O-vinyl ethers and imino ketones or imino aldehydes along the reaction pathway were determined by high-temperature (1)H, (2)H{(1)H}, and (13)C{(1)H} NMR experiments. X-ray crystallographic evidence was used to further support the mechanistic hypothesis.

Regioselective synthesis of multisubstituted furans via metalloradical cyclization of alkynes with α-diazocarbonyls: construction of functionalized α-oligofurans

Co(III)-carbene radicals generated from activation of α-diazocarbonyls by Co(II)-porphyrin complexes have been shown to undergo a new type of tandem radical addition reaction with alkynes that affords five-membered furan structures. The Co(II) complex of 3,5-Di(t)Bu-IbuPhyrin, [Co(P1)], is effective in catalyzing the metalloradical cyclization reaction under neutral and mild conditions. The [Co(P1)]-catalyzed process tolerates a wide range of α-diazocarbonyls and terminal alkynes with varied steric and electronic properties, producing polyfunctionalized furans with complete regioselectivity. The catalytic synthesis features a high degree of functional group tolerance and can be applied iteratively to construct functionalized α-oligofurans.

Regio- and stereoselective synthesis of cyclic imidates via electrophilic cyclization of 2-(1-alkynyl)benzamides. A correction

The electrophilic cyclization of 2-(1-alkynyl)benzamides affords high yields of cyclic imidates, instead of the previously reported isoindolin-1-ones, where cyclization proceeds on the oxygen of the carbonyl group rather than the nitrogen of the amide functionality. X-ray crystallography and spectroscopic techniques have been used to characterize the products. A correction is hereby provided in order to rectify the previous misassignment of structure.

Visible light photocatalytic synthesis of benzothiophenes

The photocatalytic reaction of o-methylthio-arenediazonium salts with alkynes yields substituted benzothiophenes regioselectively through a radical annulation process. Green light irradiation of eosin Y initiates the photoredox catalysis. The scope of the reaction was investigated by using various substituted diazonium salts and different alkynes.