Azulene-Indole Fused Polycyclic Heteroaromatics

Linear polycyclic systems are promising candidates in the area of organic electronics. Herein, we present the syntheses of three azulene-indole (AzIn) fused polycyclic heteroaromatics (PHAs), AzIn - 1 , AzIn - 2 and DGAzIn , which have nitrogens and nonhexagonal rings simultaneously. The chemical structures, optical and electrochemical properties of three AzIn-based PHAs have been investigated, as well as their protonation behaviors with trifluoroacetic acid (TFA). All three AzIn-based PHAs exhibit narrow optical band gaps with moderate to good air stability, anti-Kasha emission and reversible stimuli-responsiveness. Furthermore, these straightforward and simple synthetic routes would provide a new entry for constructing novel azulene-embedded π-conjugates, especially for the seven-membered ring of azulene unit, wherein the regioselective transformation is not well developed.     

T-shaped platinum boryl complexes: synthesis and structure

A series of cationic T-shaped 14-electron boryl complexes of the type trans-[(Cy(3)P)(2)Pt{B(X)X'}](+) (X=Br; X'=ortho-tolyl, tBu, NMe(2), piperidyl, Br; XX'=(NMe(2))(2), catecholato) were synthesized by halide abstraction from trans-[(Cy(3)P)(2)Pt(Br){B(X)X'}] (Cy=cyclohexyl) with Na[BAr(f) (4)] (Ar(f)=3,5-(CF(3))(2)C(6)H(3)), K[B(C(6)F(5))(4)], or Na[BPh(4)]. X-ray diffraction studies were performed on all compounds, revealing a subtle correlation between the trans-influence of the boryl moiety and the Pt--H and Pt--C separations. However, no notable agostic C--H interaction with the platinum center was detected. trans-[(Cy(3)P)(2)Pt(BCat)](+) (Cat=catecholato), the complex with the shortest Pt--H and Pt--C distances, was treated with Lewis bases (L), forming compounds of the type trans-[(Cy(3)P)(2)Pt(L)(BCat)](+), thus proving a decisive influence of the degree of trans-influence exerted by the boryl ligands on the chemical reactivity of the title complexes. Another point that was investigated and clarified is the different behavior of trans-[(Cy(3)P)(2)Pt(Br){B(Br)Mes}] (Mes=mesityl) towards K[B(C(6)F(5))(4)] with formation of the borylene species trans-[(Cy(3)P)(2)Pt(Br)(BMes)](+).     

Copper‐Catalyzed Intermolecular Asymmetric Propargylic Dearomatization of Indoles

The first copper‐catalyzed intermolecular dearomatization of indoles by an asymmetric propargylic substitution reaction was developed. This method provides a highly efficient synthesis of versatile furoindoline and pyrroloindoline derivatives containing a quaternary carbon stereogenic center and a terminal alkyne moiety with up to 86 % yield and 98 % ee.     

Tuning the Reactivity of Isocyano Group: Synthesis of Imidazoles and Imidazoliums from Propargylamines and Isonitriles in the Presence of Multiple Catalysts

The reaction of propargyl amines with tert‐butylisonitrile in the presence of a catalytic amount of both Yb(OTf)₃ and AgOTf afforded imidazoles, whereas the same reaction with primary and secondary alkylisonitriles, as well as arylisonitriles, in the presence of three metal salts [Yb(OTf)₃/AgOTf/KOTf] resulted in the 1,3,4,5‐tetrasubstituted imidazoliums in excellent yields. Both chiral amines and chiral isonitriles can be used to provide corresponding chiral heterocycles without racemization. In this multiple catalytic system, Yb(OTf)₃ catalyzed the insertion of isonitriles to the N? H bond of amines, AgOTf catalyzed the 5‐exo‐dig cyclization of the resulting amidine nitrogen to the tethered triple bond, and KOTf promoted the salt metathesis, thus providing at the same time the counterion to the imidazolium. Against common knowledge, the isocyano group acted in these reactions as a polarized triple bond instead of conventional carbene‐like function.     

A General and Mild Catalytic α‐Alkylation of Unactivated Esters Using Alcohols

Catalytic α‐alkylation of esters with primary alcohols is a desirable process because it uses low‐toxicity agents and generates water as the by‐product. Reported herein is a NCP pincer/Ir catalyst which is highly efficient for α‐alkylation of a broad scope of unactivated esters under mild reaction conditions. For the first time, alcohols alkylate unactivated α‐substituted acyclic esters, lactones, and even methyl and ethyl acetates. This method can be applied to the synthesis of carboxylic acid derivatives with diverse structures and functional groups, some of which would be impossible to access by conventional enolate alkylations with alkyl halides.     

Access to Nitriles from Aldehydes Mediated by an Oxoammonium Salt

A scalable, high yielding, rapid route to access an array of nitriles from aldehydes mediated by an oxoammonium salt (4‐acetylamino‐2,2,6,6‐tetramethylpiperidine‐1‐oxoammonium tetrafluoroborate) and hexamethyldisilazane (HMDS) as an ammonia surrogate has been developed. The reaction likely involves two distinct chemical transformations: reversible silyl‐imine formation between HMDS and an aldehyde, followed by oxidation mediated by the oxoammonium salt and desilylation to furnish a nitrile. The spent oxidant can be easily recovered and used to regenerate the oxoammonium salt oxidant.     

Palladium-catalyzed amidation by chemoselective C(sp3)-H activation: concise route to oxindoles using a carbamoyl chloride precursor

Quite select: a new strategy was developed for the synthesis of various oxindoles from carbamoyl chlorides. Under the optimum reaction conditions, with Ad(2)PBu as a ligand, tBuCONHOH as an additive, and a CO atmosphere, selective C(sp(3))-H activation proceeded in the presence of a C(sp(2))-H bond. Ad=adamantyl.     

Synthesis by radical cyclization and cytotoxicity of highly potent bioreductive alicyclic ring fused [1,2-a]benzimidazolequinones

The key step in the synthesis of new five, six and seven-membered alicyclic ring [1,2-a]-fused bioreductive benzimidazolequinones was radical cyclisation. Six and seven-membered tributyltin hydride-mediated homolytic aromatic substitutions of nucleophilic N-alkyl radicals onto the benzimidazole-2-position occurred in high yields (63-70 %) when quaternising the pyridine-like 3-N of imidazole with camphorsulfonic acid and using large excesses of the azo-initiator, 1,1'-azobis(cyclohexanecarbonitrile), to supplement the non-chain reaction. Elaboration of benzimidazoles to the benzimidazolequinones occurred in excellent yields. The IC50 values for the cytotoxicity of benzimidazolequinones towards the human skin fibroblast cell line GM00637 were in the nanomolar range, as determined by using the MTT assay. The benzimidazolequinones were much more cytotoxic than indolequinone analogues. 1,2,3,4-Tetrahydropyrido[1,2-a]benzimidazole-6,9-dione was the most potent compound prepared being more than 300 times more cytotoxic than the clinically used bioreductive drug, mitomycin C. The latter benzimidazolequinone was more potent under hypoxic conditions (associated with solid tumors), being 4.4 times more cytotoxic than under aerobic conditions, while mitomycin C was 1.8 times more selective towards hypoxia. The cyclopropane fused pyrido[1,2-a]benzimidazolequinone, 1a,2,3,9b-tetrahydro-1H-cyclopropa[3,4]pyrido[1,2-a]benzimidazole-5,8-dione was less cytotoxic and selective than the five-membered ring analogue, 1,1a,8,8a-tetrahydrocyclopropa[3,4]pyrrolo[1,2-a]benzimidazole-3,6-dione. Modifying the structure of the most potent pyrido[1,2-a]benzimidazolequinone by attaching methyl substituents onto the quinone moiety increased reductive potentials and decreased cytotoxicity and selectivity towards hypoxia.