[reaction: see text] The first cyclopropanation reaction of olefins with Fischer dialkylaminocarbene complexes is presented. The reaction yields 1-aminocyclopropanecarboxylic acid derivatives in a single step, usually with high diastereoselectivity. An approach to the asymmetric version of this reaction is also presented. The synthetic utility of the procedure is exemplified by the synthesis of both cycles of metanoproline in a single step. In addition, the synthesis of the first Fischer carbene containing a halocarbonyl group is reported.
A series of chelated tetracarbonyl aminovinyl carbene complexes 5 are prepared by high-yielding decarbonylation reaction. γ-Alkyl-substituted complexes 5a-d are stable in solid form while γ-aryl-substituted analogues 5e-g are stable only in solution. NMR studies determined that complexes 5 undergo a dynamic process in solution, in which the unsaturated η 1 species are present in low concentration. Reaction of complexes 5 with electron-deficient alkynes under controlled conditions afforded the 1,4,5-η 3 -dienylcarbene complexes 9 arising from the insertion of the alkyne in the metal-carbon bond. The stability and behavior of these complexes were studied and found to be related to their electronic structure and pattern of substitution. Thermal decomposition of carbenes 9 produced either cyclopentadienes 13 or phenol derivatives 15, the major products in the Do ¨tz reaction, thus demonstrating that they can be the actual intermediates in this reaction. The overall process can be considered a Do ¨tz reaction carried out in three separate steps at low temperature.
[reaction: see text] A sequential acylation-intramolecular cyclopropanation reaction takes place upon treatment of a series of tetraalkylammonium acylchromates with beta,gamma-unsaturated acyl chlorides at -10 degrees C. The reaction leads to 2-oxabicyclo[3.1.0]hexan-3-ones with exo selectivity in good yields. The diastereoselectivity of the reaction allows the preparation of cis-divinyl cyclopropanes, which evolve via Cope sigmatropic reaction toward cycloheptadiene derivatives. Furthermore, the aromatic Cope rearrangement of a series of cis-aryl vinyl cyclopropanes prepared by means of this methodology has been studied.
Dynamic sophisticated real-time adaptation is not possible with current e-learning technologies. Our proposal is based on changing the approach for the development of e-learning systems using dynamic languages and including them in both platforms and learning content specifications thereby making them adaptive. We propose a Sharable Auto-Adaptive Learning Object (SALO), defined as an object that includes learning content and describes its own behaviour supported by dynamic languages. We describe an example implementation of SALO for the delivery and assessment of a web development course using Moodle rubrics. As a result, the learning objects can dynamically adapt their characteristics and behaviour in e-learning platforms.
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