Palladium-Catalyzed Highly Chemo-, Regio-and Stereoselective Synthesis of Eight- to Ten-Membered Lactones from Allenyl 3-Oxoalkanoates and Organic Halides

A highly chemo-, regio-, and stereoselective synthesis of eight-to ten-membered lactones via the coupling cyclization of readily available allenyl 3-oxoalkanoates and organic halides through an anti-pi-allylic palladium intermediate is reported. The yields ranged from moderate to good

Electrophilic Cyclization of 2-(2 ',3 '-Allenyl)acetylacetates with Iodine Using Calcium Hydride as the Base

A facile and efficient protocol for the synthesis of 4,5-dihydrofuran derivatives via iodine-mediated cyclization of various 2-(2',3'-allenyl)acetylacetates with CaH2 as the base has been developed. The yields range from moderate to good. The resulting products can be used for further elaboration by palladium-catalyzed coupling reactions

Study on Al Evaporation during AlV55 Melting and Alloy Preparation

Vacuum induction melting is a commonly used method for preparing AlV55 alloys. However, this method results in high Al evaporation losses, leading to poor cost control. Moreover, the influence of the process parameters on the alloy composition remains unclear. In this study, the evaporation pattern of Al in the melting and preparation processes of AlV55 alloys is studied, and measures for controlling the system pressure are proposed to effectively reduce Al evaporation. The experimental results show that smelting under an Ar gas atmosphere of 2000 Pa can reduce the evaporation loss of Al from 11.48% under vacuum conditions (60 Pa) to 0.58% of the amount of raw material added, effectively improving the metal utilization rate and reducing production costs. The influence of various process parameters on the alloy composition and Al volatilization are investigated to enable the effective control of the compositional uniformity and impurity content of the resulting alloys. Under optimal conditions, the impurity contents of C, O, and N are 0.03%, 0.0073%, and 0.013%, respectively; this reduces the amount of Al lost by evaporation compared to conventional methods, and the alloy produced meets commercial standards

Palladium-Catalyzed Decarboxylation of Allenyl 3-Oxoalkanoates: An Efficient Synthesis of 3,4-Allenyl Ketones

An efficient synthesis of 3,4-allenyl ketones via the Pd-catalyzed decarboxylative coupling of the readily available 3-oxoalkanoates is reported. The C–C bond forming reaction occurs under mild conditions producing CO₂ as the only byproduct

Effect of CaCl2 on Microstructure of Calciothermic Reduction Products of Ti2O3 to Prepare Porous Titanium

The compound CaCl2 plays a significant role in the process of direct calciothermic reduction of Ti2O3 to prepare porous titanium. In this paper, the effect of CaCl2 on reduction products by calciothermic reduction of Ti2O3 was investigated. Results show that the distribution of CaCl2 in reduction preform influences particle size and morphology differences in reduction products both on the surface and the inside. The CaCl2 is transferred to the surface of the Ti2O3 preform due to its volatilization before and throughout reduction. The content of CaCl2 in the surface zone of Ti2O3 preform is significantly higher than that in the interior during the reduction process, contributing to the formation of large Ti particles with a smooth shape on the surface, and small Ti particles with inherited morphology of Ti2O3 inside. More CaCl2 causes the aggregation of Ti particles to form large Ti particles which are advantageous as they connect and form a more solid porous titanium structure. The presence of a small amount of CaCl2 in the interior also results in the coexistence of small Ti and CaO particles, forming a loose structure with uniform distribution

Study on the behavior of impurities in zone melting of aluminum

In this study, the migration and distribution behaviors of Cu, Si, Fe, and Ti impurities in the process of preparing high-purity Al by zone melting under an argon atmosphere were investigated. The width of the molten zone during the experiment was determined as 40 mm, based on simulation calculation results. The influences of the travel speed of the molten area and number of zone melting times on the migration and distribution of the Cu, Si, Fe, and Ti impurities in the Al were experimentally demonstrated. The contents of the impurities Cu, Si, Fe, and Ti in the middle of the sample (i.e., 140 mm from the head end) were 0.9057, 0.8116, 0.1202, and 0.4237 ppm, respectively, when the travel speed of the molten area was 1.0 mm/min and with 15 times of zone melting. The contents of all the above impurities were reduced to the requirements of Chinese national standard and 99.9995% (i.e., 5N5) high-purity Al was obtained from 4 N Al by the zone melting method under the above optimal experimental conditions. The experimental results show that the effect of the number of zone melting times on the removal of the Cu, Si, and Fe impurities is more evident, and that these impurities are easier to separate than Ti. Therefore, high-purity Al with lower Cu, Si, and Fe contents can be obtained by optimizing the travel speed of the molten area and number of zone melting times

Patrones de aprendizaje en universitarios Latinoamericanos: Dimensión cultural e implicaciones educativas

La presente investigación explora y discute el modelo de patrones de aprendizaje definido por Vermunt (1998), y su relación con ciertos factores personales, contextuales y el rendimiento académico. En la muestra participaron un total de 354 estudiantes de primer curso de la carrera Ciencias de la Educación; los mismos pertenecen a 3 países latinoamericanos (Colombia, México y Venezuela) que se distribuyen en 4 universidades diferentes. Del total de participantes, 262 fueron estudiantes femeninas y 92 estudiantes masculinos. A las mismas se aplica una versión adaptada al español internacional Inventario de Estilos de Aprendizaje (ILS) y un cuestionario de datos socio-demográfico, mediante el cual se indagan los factores personales, contextuales (edad, género, esfuerzo, dedicación al estudio, percepción de la docencia y dominio específico) y el rendimiento académico. Los resultados reportan una estructura empírica de cuatro patrones de aprendizaje, en donde tres (MD, RD y UD) coinciden con la propuesta clásica de Vermunt. A su vez, en cada una de las muestras aparece otro patrón normalmente conformado por creencias o motivos para estudiar (PI y PM) más propios de estudiantes de educación Secundaria. Estas particularidades del territorio latinoamericano, se discuten en el marco de la dimensión intercultural. Asimismo, se hallan ciertas diferencias significativas en relación a factores tales como el género, el esfuerzo, la dedicación al estudio, la percepción de la docencia y el rendimiento académico. Por último, se exponen las limitaciones del estudio y perspectivas futuras.This research explores and discusses the learning pattern model defined by Vermunt’s (1998); and its relationship with personal and contextual factors and academic performance. In the sample participated a total of 354 students of first-year of Educational Sciences. The students belong to three Latin-American countries (Colombia, México and Venezuela) and they are distributed in four different universities. The participants were 262 females and 92 males’ students. Data collection was carried out using the Inventory of Learning Style (Vermunt, 1998); and a socio-demographic questionnaire with a set of questions about the students’ age, gender, dedication to study, perception of teaching, effort and academic performance were collected. The results report an empirical structure of four learning patterns, where three (MD, RD and UD) coincide with the classical Vermunt proposal. In addition, in each of the samples there appears another pattern normally conformed by beliefs or motives to study (PI and PM) more typical of students of Secondary education. These particularities of the Latin American territory are discussed within the framework of the cross-cultural dimension. Likewise, there are some significant differences in relation to certain factors such as gender, effort, dedication to study, perception of teaching and academic performance. Finally, the limitations of the study and future perspectives are presented

Asymmetric Formal Synthesis of the Long-Acting DPP-4 Inhibitor Omarigliptin

A highly efficient asymmetric synthesis of the key tetrahydropyranol intermediate of DPP-4 inhibitor omarigliptin (<b>1</b>) is described. The successful development of a protecting-group- and precious-metal-free synthesis was achieved via the discovery of a practical asymmetric Henry reaction and the application of a one-pot nitro-Michael–lactolization–dehydration through-process. Other features of the synthesis include a highly efficient MsCl-mediated dehydration and a crystallization-induced dynamic resolution for exceptional ee and dr upgrade. The synthesis of this complex intermediate utilizes simple starting materials and proceeds in four linear steps

Development of an Efficient Route to 2-Ethynylglycerol for the Synthesis of Islatravir

The unnatural, alkyne-containing nucleoside analog islatravir (MK-8591) is synthetically accessed through a biocatalytic cascade starting from 2-ethynylglycerol as a building block. Herein, we describe the development of an efficient synthesis of this building block including the initial route, route scouting and final process development. Key challenges that have been overcome are the development of an efficient and safe acetylenic nucleophile addition to an appropriate ketone, and the identification of a 2-ethynylpropane-1,2,3-triol derivative with favorable physical properties. An acid-catalyzed cracking of commercially available 1,3-dihydroxyacetone dimer and subsequent 1,2-addition of an acetylenic nucleophile has been discovered and optimized into the manufacturing proces