A rhodamine based chemosensor for solvent dependent chromogenic sensing of cobalt (II) and copper (II) ions with good selectivity and sensitivity: Synthesis, filter paper test strip, DFT calculations and cytotoxicity.

A new chemosensor 1 was synthesized by reacting rhodamine B hydrazide and 2,3,4-trihydroxybenzaldehyde, which was then characterized by spectroscopic techniques and single crystal X-ray crystallography. Sensor 1 has the ability to sense Co2+/Cu2+ ions by "naked-eye" with an apparent colour change from colourless to pink in different solvent system, MeCN and DMF respectively. Furthermore, it can selectively detect Co2+/Cu2+ among wide range of different metal ions, and it exhibits low detection limit of 4.425 × 10-8 M and 1.398 × 10-7 M respectively. Binding mode of the two complexes were determined to be 1:1 stoichiometry for Co2+ complex and 1:2 stoichiometry for Cu2+ complex through Job's plot, IR spectroscopy, mass spectrometry and 1H NMR spectroscopy. Moreover, reversibility of the sensor 1 as copper (II) ion detector was determined by using EDTA and the results showed that sensor 1 can be reused for at least 6 cycles. Other than that, a low cost chemosensor test strips were fabricated for the convenient "naked-eye" detection of Co2+ and Cu2+ in pure aqueous media. The MTT assay was conducted in order to determine the cytotoxicity of sensor 1 towards human cell lines.

Acetal Addition to Electron-Deficient Alkenes with Hydrogen Atom Transfer as a Radical Chain Propagation Step.

We describe a visible-light-promoted addition of a hydrogen atom and an acetal carbon toward various electron-deficient alkenes. 1,3-Dioxolane is converted to its radical species in the presence of persulfate and an iridium catalyst upon visible light irradiation, which then reacts with electron-deficient alkenes. The reaction operates via a radical chain mechanism, a less commonly observed pathway for this class of transformation. Hydrogen atom transfer from 1,3-dioxolane to α-malonyl radicals is corroborated by experimental and density functional theory studies.

Total Synthesis of the Reported Structure of Stresgenin B Enabled by the Diastereoselective Cyanation of an Oxocarbenium.

We report the first total synthesis of the reported structure of the heat shock protein expression inhibitor stresgenin B. The synthesis features (1) diastereoselective cyanation of an oxocarbenium intermediate en route to the synthetically challenging α-amido dioxolane, (2) Pd-catalyzed hydration of an unstable nitrile, and (3) late-stage Au-catalyzed Meyer-Schuster rearrangement or Ce-mediated Peterson olefination to furnish the exocyclic α,ß-unsaturated ester. Our synthetic endeavors allowed us to conclude that the structure of stresgenin B requires revision.

Expedient synthesis of highly substituted pyrroles via tandem rearrangement of α-diazo oxime ethers.

An efficient rhodium-catalyzed synthesis of 2H-azirines and pyrroles has been developed. Novel rearrangement of α-oximino ketenes derived from α-diazo oxime ethers provides 2H-azirines bearing quaternary centers and allows for subsequent rearrangement to highly substituted pyrroles in excellent yields.