Mechanism Analysis of Bubble Discharge Within Silicone Gels Under Pulsed Electric Field.

Silicone gel, used in the packaging of high-voltage, high-power semiconductor devices, generates bubbles during the packaging process, which accelerates the degradation of its insulation properties. This paper establishes a testing platform for electrical treeing in silicone gel under pulsed electric fields, investigating the effect of pulse voltage amplitude on bubble development and studying the initiation and growth of electrical treeing in a silicone gel with different pulse edge times. The relationship between bubbles and electrical treeing in silicone gel materials is discussed.

Chiral phosphoric acid-catalyzed transfer hydrogenation of 3,3-difluoro-3-indoles.

A convenient and efficient method for the synthesis of optically active difluoro-substituted indoline derivatives starting from the corresponding 3-indoles by chiral phosphoric acid-catalyzed transfer hydrogenation was developed. Using Hantzsch ester as the hydrogen source under mild reaction conditions, the target products can be obtained with excellent yield and enantioselectivity.

Thiol-Catalyzed Photodriven Stereoselective Hydrodifluoroacetylative Cyclization of Alkyne.

A metal-free protocol for visible-light-driven intramolecular hydrodifluoroacetylative cyclization of -propargyl or -homopropargyl-2-bromo-2,2-difluoroacetamide to α,α-difluorinated β-substituted γ- or δ-lactam without an additional photosensitizer has been developed. By using thiol and Hantzsch ester as the catalyst and hydrogen donor, respectively, to implement a hydrogen atom transfer process, moderate to high () selectivity was achieved. The results of a mechanistic investigation revealed the critical contribution of the thiol catalyst in attaining the stereoselectivity.

Ni-Catalyzed enantioselective reductive arylcyanation/cyclization of -(2-iodo-aryl) acrylamide.

A Ni/(,)-BDPP-catalyzed intramolecular Heck cyclization of -(2-iodo-aryl) acrylamide with 2-methyl-2-phenylmalononitrile was developed to give oxindoles with good enantioselectivities. We found that utilizing such an electrophilic cyanation reagent could tackle the deleterious effect of the coordinative cyanide ion in the asymmetric alkene arylcyanation.

Access to α-Cyano Carbonyls Bearing a Quaternary Carbon Center by Reductive Cyanation.

Reductive cyanation of tertiary alkyl bromides using electrophilic cyanating reagent and zinc reductant was developed, providing various α-cyano ketones, esters, and carboxamides containing a nitrile-bearing all-carbon quaternary center in good to excellent yields under mild reaction conditions. The corresponding reaction mechanism involving in situ generated organozinc reagent and reactivity distinction was elucidated by density functional theory computation.

Iridium-Catalyzed Distal Hydroboration of Aliphatic Internal Alkenes.

The regioselective hydroboration of aliphatic internal alkenes remains a great challenge. Reported herein is an iridium-catalyzed hydroboration of aliphatic internal alkenes, providing distal-borylated products in good to excellent yields with high regioselectivity (up to 99:1). We also demonstrate that the C-B bond of the distal-borylated product can be readily converted into other functional groups.