Light-induced destabilisation of oil-in-water emulsions using light-active bolaform surfactants.

External stimuli-induced destabilisation of oil-in-water emulsions is of both fundamental and technological importance. In this work we synthesize light-active bolaform-type surfactants (LABSs) and show the preparation of decane-in-water emulsions over a range of surfactant and salt concentrations. Under ultraviolet (UV) illumination, LABSs undergo trans to cis isomerization affecting their interfacial activity. Therefore when stable emulsions stabilized by LABSs are exposed to UV light, they undergo partial destabilization. To induce interfacial flow, a small amount of volatile solvent (methanol, ethanol, tetrahydrofuran, etc.) is added at the emulsification stage and in this case complete phase separation is observed. This study demonstrates a facile route to induce destabilization of surfactant-stabilized emulsions using benign solvents and minimal use of energy (UV light) and this method could be of importance in wastewater treatment, enhanced oil recovery, protein separation, etc. where emulsion destabilization is desired.

Cobalt(III)-Catalyzed Regio- and Chemoselective [4 + 2]-Annulation of N-Chlorobenzamides/Acrylamides with 1,3-Dienes at Room Temperature.

Co(III)-catalyzed regio- and chemoselective redox-neutral C-H annulation of arylamides/acrylamides with 1,3-dienes is described. The present annulation reaction was well suited with a less-reactive 1,3-butadiene. By employing this protocol, pharmaceutically important 3,4-dihydroisoquinolinones were synthesized in good yields. Furthermore, the prepared 3,4-dihydroisoquinolinones were converted into highly important oxirane derivatives in good yields. A plausible mechanistic cycle is proposed and supported by a competition experiment and kinetic isotopic effect (KIE) studies.

Ru(II)- or Rh(III)-Catalyzed Annulation of Aromatic/Vinylic Acids with Alkylidenecyclopropanes via C-H Activation.

An efficient and new route for the synthesis of (E)-4-benzylideneisochroman-1-ones through tandem cascade annulation of benzoic acids with alkylidenecyclopropanes using Ru(II) as a catalyst is demonstrated. It is important to note that the reaction delivers selectively E-stereoselective 4-benzylideneisochroman-1-one derivatives in moderate to good yields, which has completely diverse selectivity as compared with previous methods. Further, the annulation was explored with less-reactive ß C-H activation of vinylic acids with alkylidenecyclopropanes, leading to the highly useful α-pyrone derivatives in the presence of an Rh(III) catalyst.

Cobalt(III)-Catalyzed Chemo- and Regioselective [4 + 2]-Annulation of Aromatic Sulfoxonium Ylides with 1,3-Diynes.

Air-stable, highly abundant, and cost-effective Co(III)-catalyzed redox-neutral [4 + 2]-annulation of aromatic sulfoxonium ylides with 1,3-diynes providing useful substituted 1-naphthol derivatives in a regioselective manner is described. Further, the prepared 1-naphthols having internal alkyne were converted into useful polycarbocyclic molecules and spiro-dienone derivatives in good-to-excellent yields. A possible reaction mechanism involving ortho C-H activation as a key step was proposed and supported by deuterium labeling and kinetic isotope labeling studies.

Cobalt(iii)-catalyzed redox-neutral [4+2]-annulation of N-chlorobenzamides/acrylamides with alkylidenecyclopropanes at room temperature.

An efficient synthesis of substituted 3,4-dihydroisoquinolinones through [4+2]-annulation of N-chlorobenzamides/acrylamides having a monodentate directing group with alkylidenecyclopropanes in the presence of a less expensive, highly abundant and air stable Co(iii) catalyst via a C-H activation is demonstrated. In this reaction, the N-Cl bond of N-chlorobenzamide serves as an internal oxidant and thus an external metal oxidant is avoided. The 3,4-dihydroisoquinolinone derivatives are converted successfully into the highly useful imidoyl chloride derivatives. The deuterium labeling and kinetic isolabelling studies reveal that the C-H activation is a rate-determining step in this cyclization reaction.

Rhodium(III)-Catalyzed Redox-Neutral 1,1-Cyclization of N-Methoxy Benzamides with Maleimides via C-H/N-H/N-O Activation: Detailed Mechanistic Investigation.

An Rh(III)-catalyzed 1,1-cyclization of N-methoxy benzamides with maleimides providing isoindolinone spirosuccinimides through N-H/C-H/N-O bond activation is described. The detailed mechanistic investigation including isolation of key metalacycle intermediate, deuterium labeling studies, and DFT calculations were performed. The computational study reveals that the AcOH that formed in the reaction medium plays a key role in the N-OMe bond cleavage and the oxidation of Rh(I) to Rh(III).

Ruthenium(II)-Catalyzed Redox-Free [3 + 2] Cycloaddition of N-Sulfonyl Aromatic Aldimines with Maleimides.

A ruthenium(II)-catalyzed redox-free cycloaddition of N-sulfonyl aromatic aldimines with maleimides providing 1-aminoindanes in good yields is described. Usually, maleimides reacted with substituted aromatics, affording the Michael-type ortho alkylated aromatics or 1,1-type cyclized spirosuccinimides. In the present reaction, maleimides provided 1,2-type cycloaddition products. The proposed mechanism was strongly supported by the DFT calculations and isolation of a ruthenacycle intermediate.

Ruthenium-Catalyzed Remote C-H Sulfonylation of N-Aryl-2-aminopyridines with Aromatic Sulfonyl Chlorides.

A ruthenium-catalyzed remote sulfonylation at the C5 position of the pyridine group of N-aryl-2-aminopyridines with aromatic sulfonyl chlorides is described. The mechanistic and deuterium labeling studies clearly reveal that the ruthenametallacycle is a key intermediate in the reaction, which forms via the C-H bond activation. The DFT calculation supports that the C5 position of the 2-aminopyridine group carries a more negative charge (-0.304) as compared with other carbons in the metalacycle intermediate.