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1. Construction of Diazo Compounds via Catalytic [3 + 2] Annulation of Vinyldiazoacetates and Their Synthetic Applications

   https://doi.org/10.1021/acscatal.4c01291  

   Bao, Ming; Navarrete_Carriola, Diana Victoria; Wherritt, Daniel; Doyle, Michael P (May 2024, ACS Catalysis)

   Highly selective formal [3 + 2]-cycloaddition of vinyldiazoacetates with quinone ketals and quinoneimine ketals has been accomplished at room temperature with catalytic amounts of the Brønsted acid triflimide, leading to highly functionalized diazoacetates in good yields. The vinyldiazonium ion generated by electrophilic addition to the vinylogous position of the reactant vinyldiazo compound is the key intermediate in this selective transformation. Both oximidovinyldiazoacetates and those with other vinyl substituents undergo cycloaddition reactions with quinone ketals whose products, after extended reaction times, undergo substrate-dependent 1,2-migration; catalysis by Rh2(OAc)4, HNTf2, and Sc(OTf)3 effects these 1,2-migrations to the same products. However, the products from HNTf2-catalyzed reactions between quinoneimine and oximidovinyldiazoacetates undergo Rh2(OAc)4-catalyzed 1,3-C−H insertion. 1,3-Difunctionalization products are obtained for electrophilic reactions of Eschenmoser’s salt with selected vinyldiazoacetates, but with α-dibenzylaminomethyl ether, 1,6-hydride transfer reactions are observed with oximidovinyldiazoacetates. 

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2. Determination of anisotropic optical properties of MOCVD grown m-plane α-(Al _x Ga _1−x ) ₂ O ₃ alloys

   https://doi.org/10.35848/1347-4065/acd095  

   Kluth, Elias; Anhar Uddin Bhuiyan, A. F. M.; Meng, Lingyu; Bläsing, Jürgen; Zhao, Hongping; Strittmatter, André; Goldhahn, Rüdiger; Feneberg, Martin (May 2023, Japanese Journal of Applied Physics)

   Abstract The anisotropic dielectric functions (DF) of corundum structuredm-planeα-(Al_xGa_1−x)₂O₃thin films (up tox= 0.76) grown onm-plane sapphire substrate by metalorganic CVD have been investigated. IR and visible–UV spectroscopic ellipsometry yields the DFs, while X-ray diffraction revealed the lattice parameters (a,m,c), showing the samples are almost fully relaxed. Analysis of the IR DFs from 250 to 6000 cm⁻¹by a complex Lorentz oscillator model yields the anisotropic IR active phononsE_uandA_2uand the shift towards higher wavenumbers with increasing Al content. Analyzing the UV DFs from 0.5 to 6.6 eV we find the change in the dielectric limitsε_∞and the shift of the Γ-point transition energies with increasing Al content. This results in anisotropic bowing parameters forα-(Al_xGa_1−x)₂O₃ofb_⊥= 2.1 eV andb_∣∣= 1.7 eV. 

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3. Phosphine-catalyzed activation of cyclopropenones: a versatile C ₃ synthon for (3+2) annulations with unsaturated electrophiles

   https://doi.org/10.1039/D2SC04092A  

   He, Xin; Ma, Pengchen; Tang, Yuhai; Li, Jing; Shen, Shenyu; Lear, Martin J.; Houk, K. N.; Xu, Silong (November 2022, Chemical Science)

   We herein report a phosphine-catalyzed (3 + 2) annulation of cyclopropenones with a wide variety of electrophilic π systems, including aldehydes, ketoesters, imines, isocyanates, and carbodiimides, offering products of butenolides, butyrolactams, maleimides, and iminomaleimides, respectively, in high yields with broad substrate scope. An α-ketenyl phosphorous ylide is validated as the key intermediate, which undergoes preferential catalytic cyclization with aldehydes rather than stoichiometric Wittig olefinations. This phosphine-catalyzed activation of cyclopropenones thus supplies a versatile C 3 synthon for formal cycloadditon reactions. 

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4. Synthesis of Heterocycles by HNTf2-Catalyzed C–H Functionalization of Vinyldiazo Compounds with 3-Phenyl-3-hydroxyisoindolinone

   https://doi.org/10.1055/a-2360-8359  

   Bao, Ming; Arman, Hadi; Doyle, Michael P (July 2024, Synthesis)

   Abstract A Brønsted acid catalyzed C–H functionalization of vinyldiazoacetates with 3-hydroxyisoindolinone is developed. This methodology provides a general access to E-substituted isoindolinone vinyldiazo compounds in good yields and excellent diastereoselectivities with broad substrate generality under mild conditions, and with 4-substituted 2-diazo-3-butenoates produces fused bicyclic pyrrolidines. The reaction generally involves addition of the N-acyl ketiminium electrophile, formed from the 3-hydroxyisoindolinone, to the vinylogous position of the vinyldiazo compound resulting in vinyldiazonium ion intermediates that undergo deprotonation to new vinyldiazo compounds or ring closure to fused bicyclic pyrrolidines. 

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5. Molecular Gas Properties and CO-to-H ₂ Conversion Factors in the Central Kiloparsec of NGC 3351

   https://doi.org/10.3847/1538-4357/ac382f  

   Teng, Yu-Hsuan; Sandstrom, Karin M.; Sun, Jiayi; Leroy, Adam K.; Johnson, L. Clifton; Bolatto, Alberto D.; Kruijssen, J. M.; Schruba, Andreas; Usero, Antonio; Barnes, Ashley T.; et al (January 2022, The Astrophysical Journal)

   Abstract The CO-to-H 2 conversion factor ( α CO ) is critical to studying molecular gas and star formation in galaxies. The value of α CO has been found to vary within and between galaxies, but the specific environmental conditions that cause these variations are not fully understood. Previous observations on ~kiloparsec scales revealed low values of α CO in the centers of some barred spiral galaxies, including NGC 3351. We present new Atacama Large Millimeter/submillimeter Array Band 3, 6, and 7 observations of 12 CO, 13 CO, and C 18 O lines on 100 pc scales in the inner ∼2 kpc of NGC 3351. Using multiline radiative transfer modeling and a Bayesian likelihood analysis, we infer the H 2 density, kinetic temperature, CO column density per line width, and CO isotopologue abundances on a pixel-by-pixel basis. Our modeling implies the existence of a dominant gas component with a density of 2–3 × 10 3 cm −3 in the central ∼1 kpc and a high temperature of 30–60 K near the nucleus and near the contact points that connect to the bar-driven inflows. Assuming a CO/H 2 abundance of 3 × 10 −4 , our analysis yields α CO ∼ 0.5–2.0 M ⊙ (K km s −1 pc 2 ) −1 with a decreasing trend with galactocentric radius in the central ∼1 kpc. The inflows show a substantially lower α CO ≲ 0.1 M ⊙ (K km s −1 pc 2 ) −1 , likely due to lower optical depths caused by turbulence or shear in the inflows. Over the whole region, this gives an intensity-weighted α CO of ∼1.5 M ⊙ (K km s −1 pc 2 ) −1 , which is similar to previous dust-modeling-based results at kiloparsec scales. This suggests that low α CO on kiloparsec scales in the centers of some barred galaxies may be due to the contribution of low-optical-depth CO emission in bar-driven inflows. 

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