Ruthenium-Catalyzed Activation of Nonpolar C−C Bonds via π-Coordination-Enabled Aromatization

Activation of C−C bonds allows editing of molecular skeletons, but methods for selective activation of nonpolar C−C bonds in the absence of a chelation effect or a driving force derived from opening of a strained ring are scarce. Herein, we report a method for ruthenium-catalyzed activation of nonpolar C−C bonds of pro-aromatic compounds by means of π-coordination-enabled aromatization. This method was effective for cleavage of C−C(alkyl) and C−C(aryl) bonds and for ring-opening of spirocyclic compounds, providing an array of benzene-ring-containing products. The isolation of a methyl ruthenium complex intermediate supports a mechanism involving ruthenium-mediated C−C bond cleavage.     

Old Reagent,New Results: Aromatization of Hantzsch 1,4-Dihydropyridines with Supported Bismuth Nitrate under Microwave Irradiation in Solventless System

Hantzsch 1,4-dihydropyriines were rapidly and efficiently oxidized using bismuth nitrate supported onto silica gel under microwave irradiation.     

N,N′,N,N′-TETRABROMO-BENZENE-1,3-DISULFONYLAMIDE AS A NOVEL REAGENT FOR OXIDATIVE AROMATIZATION OF 1,3,5-TRISUBSTITUTED PYRAZOLINES UNDER HETEROGENEOUS AND SOLVENT-FREE CONDITIONS

1,3,5-Trisubstituted pyrazolines were converted to the corresponding pyrazoles in good yields under heterogeneous and solvent-free conditions by N,N′,N,N′-tetrabromo-benzene-1,3-disulfonylamide [TBBDA] at ambient temperature.     

Protecting group free syntheses of (±)-columbianetin and (±)-angelmarin

A five-step and protecting group free synthesis of (±)-columbianetin from cyclohexane-1,3-dione is reported. The former compound was converted into its p-hydroxycinnamate derivative, (±)-angelmarin, using Coster’s esterification procedure. Efforts to modify the synthesis so as to prepare angelmarin and columbianetin in an enantioselective manner are described.     

Biomimetic synthetic studies on lactonamycin: an expedient synthesis of dihydroxy-isoindolinone-carboxylates

The synthesis of dihydroxy-isoindolinone-carboxylates from a dioxinone keto-ester and N-protected sarcosine without the use of phenolic protection is described. Base-induced aromatization of the dioxinone diketo-ester followed by lactamization furnished the desired dihydroxy-isoindolinone moiety, which could be used as an EF-ring precursor toward the synthesis of lactonamycin.     

Aromatization and chemoselective alkylation of 1-methyl-3,4-dihydro-β-carboline-3-carboxylic acid and its derivatives

Unprecedented aromatization was observed during N-alkylation reactions of 1-methyl-3,4-dihydro-β-carboline-3-carboxylic acid methyl ester, giving rise to 9-alkyl-1-methyl-β-carboline-3-carboxylic acid methyl esters. Inverse addition of base during a similar reaction resulted in a chemoselective alkylation to form novel 3-butyl-1-methyl-3,4-dihydro-β-carboline-3-carboxylic acid methyl ester as the major product in good yield.     

A de novo Diels-Alder strategy toward the novel pentacyclic natural product fluostatin C: a concise synthesis of 6-deoxyfluostatin C

A conceptually new Diels-Alder approach, involving a diene moiety grafted on a preformed epoxyquinone platform and a 4-hydroxy-indenone as the dienophile, delivers the pentacyclic framework of fluostatin C in one key step.     

Anodic oxidation of a tetrasubstituted cyclooctatetraene. Multiple carbon-carbon bond cleavage and aromatization

Anodic oxidation of 1,2-,5,6-bis[trimethylene]cyclooctaetraene in methanol affords as the major product a substance formed by a complex sequence of carbon-carbon bond cleavages and concomitant aromatization.     

Synthesis of polysubstituted pyrroles from sulfinimines (N-sulfinyl imines)

Polysubstituted 2-carboxylate and 2-phosphonate pyrroles are prepared by aromatization of the corresponding 3-oxo 2-carboxylate and 2-phosphonate NH-pyrrolidines using air. Reaction of electrophiles with 3-oxo pyrrolidine dianions readily introduces substituents, regioselectively at C-4 in these pyrrolidines.     

Mechanism of Butane Transformation

Catalytic activity and aromatic selectivity of n‐butane transformation were studied over various MFI type zeolites. From the data obtained, a reaction mechanism is suggested for different catalyst systems. It is visualized that in gallium doped catalysts, Ga³⁺ directly takes part both in cracking and dehydrogenation. The [Ga CH₃]²⁺ and [GaH]²⁺ species formed during cracking and dehydrogenation require protonic sites for regeneration of Ga³⁺ species. An alternative mechanism was suggested for dehydrogenation and cracking by Ga³⁺ without the involvement of protonic sites. However a protonic site would be required for aromatization. In case of gallosilicates a one step mechanism is suggested for cracking and dehydrogenation reaction which does not require the presence of protonic sites in the catalyst system.