Construction of a discursive community during a lesson study. An example of geography in a primary French-speaking class

The aim of this article is to analyse language activity during a research lesson in geography with pupils aged 8 to 12, in the French-speaking part of Switzerland. We highlight the role of discursive modes in the construction of a discursive disciplinary community

Construction of a discursive community during a lesson study. An example of geography in a primary French-speaking class

The aim of this article is to analyse language activity during a research lesson in geography with pupils aged 8 to 12, in the French-speaking part of Switzerland. We highlight the role of discursive modes in the construction of a discursive disciplinary community

Stereoselective chromium-and molybdenum- mediated transformations of arenes*

Abstract: Tricarbonylchromium-mediated dearomatization provides a rapid access to substituted cyclohexadienes. Efficient asymmetric routes to planar chiral arene complexes and to substituted cyclohexadienes have been developed. The article sums up the main features of this chemistry. Highly enantiomerically enriched ortho-substituted benzaldehyde complexes are accessible via asymmetric lithiation followed by trapping with electrophiles. In different solvents, the trimethylsilyl complex exhibits [α] values ranging from -174 to +108 for the same enantiomer. Details of two asymmetric syntheses of natural products are given: the alkaloid lasubine I starting from a highly enantiomerically enriched planar chiral arene complex and the marine furanosesquiterpene acetoxytubipofuran. The latter is assembled via asymmetric dearomatization of a benzaldehyde imine complex. Other key steps include an Eschenmoser-Claisen rearrangement and a regio-and diastereoselective Pd-catalyzed allylic substitution. The final section deals with labile arene metal complexes. For the first time, dearomatization reactions mediated by the Mo(CO) 3 group have been realized. The reactions show strong analogies to the Cr(CO) 3 -mediated reactions, but exhibit also marked differences: the arene-Mo bond is stronger, but more labile, and the sequential double additions show different selectivities compared to the chromium analogs. The search for ever more efficient chemo-, regio-, and stereoselective routes to complex molecules from simple starting materials is an important task in organic synthesis. Progress in this area continues to advance at a fast pace. Arenes, the subject of this article, are widely available, highly stable, and readily derivatized through reactions such as electrophilic and nucleophilic aromatic substitution [1], ortholithiation followed by reaction with electrophiles [2], or metal-catalyzed substitution and coupling reactions This notwithstanding, the synthesis of complex organic molecules via elegant dearomatization chemistry has undergone intensive investigation. Examples involve the Birch reduction, which achieves *Plenary and invited lectures presented at th

Des pratiques langagières favorisant le processus de secondarisation dans le cadre de leçons de géographie au cycle 2

Ce texte part de l’hypothèse que le concept de secondarisation s’avère particulièrement fécond pour mettre en relation les pratique langagières et la construction de savoirs dans le cadre de leçons de géographie à l’école primaire. à partir d’un dispositif de recherche-formation de type Lesson Study, les auteur·e·s montrent que l’enseignement portant sur la filière de production-consommation se décline différemment au fur et à mesure que les leçons sont répétées. En effet, la tâche centrale se modifie, le registre langagier se précise et le débat prend une place plus importante. Les résultats montrent par ailleurs une dissymétrie entre le travail cognitif des élèves et celui de l’enseignant·e, ce qui rend nécessaire un renforcement de la formation des enseignant·e·s

Language practices promoting the secondarisation process as part of geography lessons in cycle 2

Ce texte part de l’hypothèse que le concept de secondarisation s’avère particulièrement fécond pour mettre en relation les pratique langagières et la construction de savoirs dans le cadre de leçons de géographie à l’école primaire. à partir d’un dispositif de recherche-formation de type Lesson Study, les auteur·e·s montrent que l’enseignement portant sur la filière de production-consommation se décline différemment au fur et à mesure que les leçons sont répétées. En effet, la tâche centrale se modifie, le registre langagier se précise et le débat prend une place plus importante. Les résultats montrent par ailleurs une dissymétrie entre le travail cognitif des élèves et celui de l’enseignant·e, ce qui rend nécessaire un renforcement de la formation des enseignant·e·s. (DIPF/Orig.)This article is based on the hypothesis that the concept of secondarisation is particularly fruitful linking language practices and knowledge construction in the context of geography lessons in primary school. Based on a Lesson Study type research-training design, authors show that teaching on the production-consumption chain takes a different form as lessons are repeated. Indeed, the central task changes, the language register becomes clearer and the debate takes on a more important role. The results also show a dissymmetry between the cognitive work of pupils and that of the teacher, which makes it necessary to strengthen teacher training. (DIPF/Orig.

Conformational Studies of ortho-Substituted Benzaldehyde Chromium Tricarbonyl Complexes

The syn/anti conformational equilibrium of o-substituted benzaldehyde chromium tricarbonyl complexes was studied by CD and 1H NMR (NOE). The preferred conformation of the o-methyl-, o-methoxy-, and o-iodobenzaldehyde complexes is anti, while those of the o-trimethyltin and o-trimethylsilyl benzaldehyde complexes is syn. The optical rotation values of (o-trimethylsilyl benzaldehyde)Cr(CO)3 ((1S)-2d) vary from -174 (in ethanol) to +108 (in chloroform)

Asymmetric Synthesis of Planar Chiral (Arene)tricarbonylchromium Complexes via Enantioselective Deprotonation by Conformationally Constrained Chiral Lithium-Amide Bases

Enantioselective lithiation/electrophile addition reactions with eight chiral Li-amide bases, 1 - 8, and five [Cr(arene)(CO)3] complexes, 9 - 13, were investigated. Restriction of conformational freedom in the chiral Li-amide base Li-1, in general, did not result in an increase in asymmetric induction. A new route to enantiomerically enriched (75 - 92%) planar chiral ortho-substituted benzaldehyde complexes via enantioselective lithiation of benzaldimine complexes 16 and 17 is reported. Within the (1S)-enantiomer series of o-substituted benzaldehyde complexes 18a - d, the sign of the specific rotation, [a], is found to be positive, except for the trimethylstannyl derivative 18b. This is interpreted in terms of a reversed conformation of the aldehyde group

Stereoselective chromium- and molybdenum-mediated transformations of arenes

Tricarbonylchromium-mediated dearomatization provides a rapid access to substituted cyclohexadienes. Efficient asymmetric routes to planar chiral arene complexes and to substituted cyclohexadienes have been developed. The article sums up the main features of this chemistry. Highly enantiomerically enriched ortho-substituted benzaldehyde complexes are accessible via asymmetric lithiation followed by trapping with electrophiles. In different solvents, the trimethylsilyl complex exhibits [alpha] values ranging from −174 to +108 for the same enantiomer. Details of two asymmetric syntheses of natural products are given: the alkaloid lasubine I starting from a highly enantiomerically enriched planar chiral arene complex and the marine furanosesquiterpene acetoxytubipofuran. The latter is assembled via asymmetric dearomatization of a benzaldehyde imine complex. Other key steps include an Eschenmoser–Claisen rearrangement and a regio- and diastereoselective Pd-catalyzed allylic substitution. The final section deals with labile arene metal complexes. For the first time, dearomatization reactions mediated by the Mo(CO)3 group have been realized. The reactions show strong analogies to the Cr(CO)3-mediated reactions, but exhibit also marked differences: the arene–Mo bond is stronger, but more labile, and the sequential double additions show different selectivities compared to the chromium analogs