The Pyrolytic Reaction of Ketonic Hydrazones from <i>S</i>-Methyl Dithiocarbazate: A Combined Online GC-MS Pyrolysis and DFT Study

The gas-phase pyrolysis of ketonic hydrazones from S-methyl dithiocarbazate R1R2CNNHC(S)SCH3 (R1, R2 = alkyl or aryl) was investigated by online GC-MS pyrolysis and theoretical calculation. Both of these pyrolytic products, ascribed to methanethiol and the corresponding N-isothiocyanate imines, were detected in the total ion chromatography (TIC) of GC-MS. Calculation results exhibit two stable configurational structures for reactants (Re), which can interconvert with relatively low barriers (3SH for syn-Re and a two-step reaction pathway for trans-Re involving tautomer interconversion followed by decomposition of CH3SH, are competitive in the reaction. Both syn-Re and trans-Re exhibit lower critical energies in the propagation step of the radical pyrolysis than that in the unimolecular pyrolysis process (187.76 kJ/mol via 131.91 kJ/mol for syn-Re, and 159.15 kJ/mol via 98.92 kJ/mol for trans-Re). However, much more energy is needed to excite the compound to produce the methylthio radical, with 262.03 and 253.60 kJ/mol for syn-Re and trans-Re, respectively. Therefore, the unimolecular pyrolysis rather than the radical one occurs in the condition of this study

Synthesis of 2-Azaanthracenes via a Sequential Sonogashira Coupling/Alkynyl Imine−Allenyl Imine Isomerization/Aza-Diels−Alder/Elimination−Aromatization Reaction

An interesting sequential Sonogashira coupling/alkynyl imine−allenyl imine isomerization/aza-Diels−Alder/elimination−aromatization reaction, providing a facile synthesis of substituted 2-azaanthracenes from 1,6-diynes and imidoyl chlorides, is reported. The easy procedure accessing the products efficiently from readily available starting materials may imply a potential synthetic application

Synthesis of 2-Azaanthracenes via a Sequential Sonogashira Coupling/Alkynyl Imine−Allenyl Imine Isomerization/Aza-Diels−Alder/Elimination−Aromatization Reaction

An interesting sequential Sonogashira coupling/alkynyl imine−allenyl imine isomerization/aza-Diels−Alder/elimination−aromatization reaction, providing a facile synthesis of substituted 2-azaanthracenes from 1,6-diynes and imidoyl chlorides, is reported. The easy procedure accessing the products efficiently from readily available starting materials may imply a potential synthetic application

Utility of Dysprosium as a Reductant in Coupling Reactions of Acyl Chlorides: The Synthesis of Amides and Diaryl-Substituted Acetylenes

Reduction of acyl chlorides with dysprosium metal has been studied. The reducing ability of dysprosium metal is solvent-dependent. Dysprosium metal, which requires neither any additive nor pretreatment, can promote the cross-coupling of acyl chlorides in DMF or DEF to give amides in good yields. When the reaction was performed in N,N-dimethylacetamide, the reductive self-coupling reaction of aroyl chloride took place smoothly and afforded the diaryl-substituted acetylenes in moderate to good yield

Stereoelectronic Substituent Effects on Silylene Insertion into the Si−Cl Bond

Density functional theory calculations for the insertions of Me2Si: into Si−Cl bonds of various chlorosilanes (YR2SiCl) revealed hitherto unnoticed remarkable stereoelectronic substituent effects on the transition state (TS) energies, suggesting the importance of the interaction between the silylene lone-pair orbital and the σ*(Si−Y) orbital at the TS

UV-Cured Transparent Flexible Silicone Materials with High Tensile Strength

Transparent flexible silicone materials are useful in electronics, sensors, coatings, and so forth. However, to the best of our knowledge, the tensile strength of unreinforced silicone rubber is lower than 0.4 MPa, and the highest tensile strength of highly transparent silicone-modified materials is no more than 1.5 MPa. The poor mechanical property limits their further application in electronic devices. Here, a kind of UV-cured transparent flexible silicone materials with tensile strength as high as 2.2 MPa were prepared by a UV-initiated thiol–ene reaction of a sulfur-containing hyperbranched polycarbosilane and a thiol silicone resin. Interestingly, their tensile strength can increase from 2.2 to 5.6 and 5.7 MPa after being immersed in an aqueous solution of 10 wt % hydrochloric acid and 10 wt % NaCl for 7 days, respectively. It is argued that the increase of the tensile strength of cured films may be attributed to the −SiOCH3 of the residual 3-trimethoxysilylpropanethiol in the sulfur-containing hyperbranched polycarbosilane. The performances of the cured materials were investigated in detail. These silicone materials exhibit transparency higher than 95% (wavenumber in the range of 400–800 nm), and the initial thermal decomposition temperatures of the cured materials are about 340 °C. These materials also show good anticorrosion property, and the mass loss of the materials immersed in the aqueous solution mediums is no more than 0.39 wt % even for 15 days

Insertion of Silylenes into Si–H and Si–Cl Bonds. Comparison of Mechanism and Substituent Effects

Electronic and steric substituent effects on the insertion reactions of dimethylsilylene (1) and 2,2,5,5-tetrasilylsilacyclopentane-1,1-diyl (2′) into Si–H bonds are compared with those into Si–Cl bonds using DFT calculations at the B3LYP/6-31++G(d,p) level. For both 1 and 2′, the ΔG⧧ value for the insertion into a Si–H bond of SiH4 is close to and only ca. 1.5 kcal mol–1 lower than that into the Si–Cl bond of H3SiCl. Effects of in-plane substituents on the ΔG⧧ values for both Si–H and Si–Cl insertion reactions are mainly electronic and electron-withdrawing substituents lower the ΔG⧧ values. Sensitivity of the Si–H insertion to the substituent effects is similar to that of the Si–Cl insertion. Effects of out-of-plane substituents are largely steric, and their sensitivity for the Si–H insertion is close to that for the Si–Cl insertion. The ΔG⧧ values for the insertion reactions of sterically bulky 2′ are significantly larger than those of 1. The puzzling prior observation that a bulky isolable silylene inserts into the Si–Cl bond of H2SiCl2 and the Si–H bond of Me2SiHCl is explained on the basis of the substituent effects on the insertion reactions

Reactions of an Isolable Dialkylgermylene with Acyl Chlorides Forming Acyl(chloro)germanes and Diacylgermanes

The reactions of isolable dialkylgermylene 1 with benzoyl and substituted benzoyl chlorides afford the corresponding aroyl­(chloro)­germanes in high yields. While 2,2-dimethylpropanoyl chloride reacts similarly, the reactions of more reactive alkanoyl chlorides such as acetyl, propanoyl, and butanoyl chlorides give rather unexpectedly the corresponding dialkanoylgermanes 3 together with alkanoyl­(chloro)­germanes 2 (2:3 = 4:1). Aroyl- and alkanoyl­(chloro)­germanes 2a–2g and dialkanoylgermanes 3e–3g obtained were fully characterized by multinuclear NMR spectroscopy, high-resolution mass spectrometry (HRMS), and by single-crystal X-ray diffraction studies for 2a and 3f. UV–vis spectra of 3e–3g and a TDDFT study of the model diacylgermanes showed two separated n → π* absorption bands, suggesting significant electronic interaction between the two carbonyl groups in a molecule through the central germanium atom

Stereoselective Formation of Eight-Membered Rings by Radical Cyclization of Silylenedioxy-Tethered Bis-methacrylate Derivatives

Radical-initiated addition of CCl₄, Cl₃CBr, PhSH, and (TMS)₃SiH to (bisisopropyl)­silylene­dioxy-tethered bis-methacrylate derivatives gives the corresponding eight-membered ring cyclic adducts stereoselectively. Hydrolysis of halo-substituted cyclic adducts with HCl in methanol affords the corresponding valerolactones, and the stereochemistry was determined by the X-ray crystallography on a dibromobenzoate derivative. DFT calculation on the eight-membered radical intermediate offers a plausible rationale for the stereoselectivity of the reaction