Selective Boryl‐Anion Migration in a Vinyl sp2−sp3 Diborane Induced by Soft Borane Lewis Acids

An intramolecular 1,2‐boryl‐anion migration from boron to carbon has been achieved by selective activation of the π system in [(vinyl)B₂Pin₂)]^? using “soft” BR₃ electrophiles (BR₃=BPh₃ or 9‐aryl‐BBN). The soft character is key to ensure 1,2‐migration proceeds instead of oxygen coordination/B?O activation. The BR₃‐induced 1,2‐boryl‐anion migration represents a triple borylation of a vinyl Grignard reagent using only B₂Pin₂ and BR₃ and forms differentially protected 1,1,2‐triborylated alkanes. Notably, by increasing the steric bulk at the β position of the vinyl Grignard reagent used to activate B₂Pin₂, 1,2‐boryl‐anion migration can be suppressed in favor of intermolecular {BPin}^? transfer to BPh₃, thus enabling simple access to unsymmetrical sp²?sp³ diboranes.     

Synthesis,Characterization, and Functionalization of 1‐Boraphenalenes

1‐Boraphenalenes have been synthesized by reaction of BBr₃ with 1‐(aryl‐ethynyl)naphthalenes, 1‐ethynylnaphthalene, and 1‐(pent‐1‐yn‐1‐yl)naphthalene and they can be selectively functionalized at boron or carbon to form bench‐stable products. All of these 1‐boraphenalenes have LUMOs localized on the planar C₁₂B core that are closely comparable in character to isoelectronic phenalenyl cations. In contrast to the comparable LUMOs, the aromatic stabilization of the C₅B ring in 1‐boraphenalenes is dramatically lower than the C₆ rings in phenalenyl cations. This is due to the occupied orbitals of π symmetry being less delocalised in the 1‐boraphenalenes.     

The action of polysilicic acid on mixed monolayers of cholesterol and lecithins

Silicic acid produces marked expansion in dipalmitoyl lecithin films and in mixed cholesterol-dipalmitoyl lecithin films with more than 50 % phospholipid. In the presence of silicic acid, these films no longer exhibit a transition region between the liquid-expanded and liquid-condensed states. Mixed cholesterol-dilauroyl lecithin.films are also expanded by silicic acid. In the absence of silicic acid, the addition of cholesterol produces greater condensation in dilauroyl lecithin films than in films of dipalmitoyl lecithin, but the reverse is the case if the substrate contains silicic acid. These results have been interpreted in terms of a possible electrostatic interaction between negatively charged dissociated silicate ions and the positively charged trimethyl ammonium group of the choline fragment.     

Transformations of manganese oxides under different thermal conditions

Thermal decomposition of various synthetic manganese oxides (MnO, Mn₃O₄, Mn₂O₃, MnOOH) and a natural manganese dioxide (MnO₂) from Gabon was studied with the help of termogravimetry in inert, oxidizing and reducing atmospheres. The compounds were characterized by XRD and electrochemical activity was tested by cyclic voltammetry using a carbon paste electrode. The natural manganese dioxide showed the best oxidizing and reducing capacity, confirmed by the lower temperatures of the transitions, the extent of the reactions and electrochemical performance in cyclic voltammograms.     

Convergent stereoselective synthesis of the visual pigment A2E

[chemical reaction: see text]. A stereoselective total synthesis of the visual pigment A2E has been achieved with use of palladium-catalyzed cross-coupling reactions in all key steps: a regioselective Suzuki or Negishi coupling of 2,4-dibromopyridine, a Sonogashira reaction, and a double Stille cross-coupling to complete the bispolyenyl skeleton.     

Asymmetric aza-Henry reactions from N-p-tolylsulfinylimines

[reaction: see text] N-Sulfinylimines derived from aromatic or aliphatic aldehydes and ketones react with nitromethane and NaOH in a highly diastereoselective manner under mild conditions. In the presence of TBAF, the reaction rates are strongly increased and the stereoselectivity is inverted. This method provides enantiomerically pure beta-nitroamines derived from enolizable aldimines and ketimines, which so far are hardly accessible by aza-Henry reactions.     

Ion-sensitive field effect transistors using carbon nanotubes as the transducing layer

We report a new type of ion-sensitive field effect transistor (ISFET). This type of ISFET incorporates a new architecture, containing a network of single-walled carbon nanotubes (SWCNTs) as the transduction layer, making an external reference electrode unnecessary. To show an example of its application, the SWCNT-based ISFET is able to detect at least 10(-8) M of potassium in water using an ion-selective membrane containing valinomycin.     

Limit of accuracy for fluorescence lifetime temperature sensing

Limit of accuracy for the fluorescence lifetime (FL) temperature-sensing method performed and marked that at lower temperature (< 400 K) it works well but for higher temperatures FL method does not found suitable. The non-radiative relaxation rate is noted to vary with increase in the temperature.     

An efficient method for the synthesis of nitropiperidones

A three step efficient strategy for the synthesis of substituted 5-nitropiperidones in high de, employing Michael addition of N-p-tolylsulfinyl beta-nitroamines to alpha,beta-unsaturated esters, hydrolysis of the sulfinyl group, and cyclization of the resulting free amines, has been developed. A very simple experimental procedure involving mild conditions and only one chromatographic purification are the main features of the process.     

Acyl‐Directed ortho‐Borylation of Anilines and C7 Borylation of Indoles using just BBr3

Indoles are privileged heterocycles found in many biologically active pharmaceuticals and natural products. However, the selective functionalization of the benzenoid moiety in indoles in preference to the more reactive pyrrolic unit is a significant challenge. Herein we report that N‐acyl directing groups enable the C7‐selective C?H borylation of indoles using just BBr₃. This transformation shows some functional‐group tolerance and notably proceeds with C6 substituted indoles. The directing group can be readily removed in situ and the products isolated as the pinacol boronate esters. Acyl‐directed electrophilic borylation can be extended to carbazoles and anilines with excellent ortho selectivity. 4‐amino‐indoles are amenable to this process, with acyl group installation and directed electrophilic C?H borylation enabling selective formation of C5‐BPin‐indoles.