Insight into the solvation and isomerization of 3-halo-1-azaallylic anions from ab initio metadynamics calculations and NMR experiments.
In organic synthesis, it is observed experimentally that the nature of the solvent can influence tremendously the reactivity and overall product selectivity. In this communication, we report on the E/Z isomerization of a typical solvated species, that is, the stable lithiated 3-chloro-3-methyl-1azaallylic anion readily accessible from the N-isopropylACHTUNGTRENNUNGimine of a-chloropropiophenone, from a theoretical and a subsequent NMR study. To date, the configurational properties of these 3-chloro-3-methyl-1-azaallylic anions are poorly understood. Our main emphasis is devoted to the monomeric species as these are believed to be the most important for further reactivity studies (see below). It will be shown that the investigated species is a particular example in which the inclusion of the solvent in the modeling study is of the utmost importance to determine the proper chemical ACHTUNGTRENNUNGbehavior. The 3-chloro-3-methyl-1-azaallylic anion was chosen as a model compound to obtain a deeper insight into the structural features of 3-halo-1-azaallylic anions and to get a better understanding, and eventually a better control, of the stereochemical outcome of the reactions in which these anions are involved. Since their first use in the early 1960s, non-halogenated 1-azaallylic anions have gained a predominant role in organic synthesis due to their ability to form new C C bonds with a lack of side products. The chemistry of 1-azaallylic anions leads to basic heterocyclic systems such as aziridines, azetidines, pyrrolidines, pyrroles, piperidines, oxiranes, oxolanes, and higher functionalized ring systems, currently of interest for pharmaceutical chemistry and agrochemistry. The application of certain halogenated counterparts, that is, the 3-chloro-3-methyl-1azaallylic anions, in particular by the group of De Kimpe and more general by the group of Florio, which incorporated the 3-chloro-3-methyl-1-azaallylic moiety into heterocyclic structures, has led to the synthesis of various important classes of compounds such as cyclopropanes, tetrahydrofurans, tetrahydropyrans, oxiranes, aziridines, chloroimines, pyrroles and pyridines, steroids, alkenylheterocycles, and oxazetidines. As mentioned, 3-chloro3-methyl-1-azaallylic anions can be used for the synthesis of functionalized oxiranes and aziridines since the former anions behave as nucleophiles in Darzensand aza-Darzenstype reactions with carbonyl compounds and imines. One of the determining factors in the stereochemical outcome of these Darzens-type reactions is the E/Z stereochemistry of the starting 1-azaallylic anion. Therefore, it is important to know and understand the configurational properties of 3chloro-3-methyl-1-azaallylic anions in order to perform aldoland Mannich-type reactions with these intermediates in a stereocontrolled manner. NMR investigation and semiempirical calculations on the stereochemistry of (2-(a-chloroethyl)benzothiazolyl)lithium and (4,4-dimethyl-2-(a-chloroethyl)oxazolinyl)lithium have demonstrated that internal coordination between lithium and chlorine stabilizes the corresponding isomer with nitrogen and chlorine at the same side of the C=C double bond. The lack of such structural investigations on 3chloro-3-methyl-1-azaallylic anions in sensu stricto urged us to study their stereochemical properties. The E/Z isomerism for non-halogenated 1-azaallylic anions has been observed and investigated quite frequently. The facile carbon carbon bond rotation in simple lithiated 1-azaallylic anions was investigated using H NMR spectros[a] Dr. R. Declerck, B. De Sterck, T. Verstraelen, Prof. Dr. M. Waroquier, Prof. Dr. V. Van Speybroeck Center for Molecular Modeling, Ghent University Proeftuinstraat 86, 9000 Gent (Belgium) Fax: (+32) 9-264-6697 E-mail : Veronique.VanSpeybroeck@UGent.be [b] Dr. G. Verniest, Dr. S. Mangelinckx, J. Jacobs, Prof. Dr. N. De Kimpe Department of Organic Chemistry, Faculty of Bioscience Engineering Ghent University, Coupure links 653, 9000 Gent (Belgium) Fax: (+32) 9-264-6243 E-mail : Norbert.DeKimpe@UGent.be Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200800948.
Regio- and stereochemical aspects in the functionalisation of a lithiated 2-(3-chloro-2-methyl-1-propenyl)-2-oxazoline: electrophile and temperature effects
4,4-Dimethyl-2-(3-chloro-2-methyl-1-propenyl)-2-oxazoline has been synthesized and deprotonated with LDA in THF to give the corresponding lithiated species, which has been found to react α-regioselectively with NH4Cl and alkyl halides, and γ-regioselectively with carbonyl compounds to afford α-protonated (or α-alkyl-substituted) regioisomers and vinyl epoxides, respectively. The Z diastereoselectivity of both the protonation and the alkylation reactions was usually found to increase with the temperature. Ab initio calculations, performed on both the naked lithium salt and the corresponding solvated form, support the observed regioselectivity.
A Study on Technology Embedded English Classes Using QR Codes
The development of information and technology has brought plenty of changes to the educational environment. The prevalence of smart phones is particularly playing a huge role in shaping learning methods. Smart phones provide the opportunity to scan QR codes, which can greatly ease access to information. Due to a high recognition speed, recognition rate, and restoration rate, they can be useful tools for English teachers to use in their class. In this study, we suggest using QR codes for writing and picture descriptions. Based on this study, more research should invest in Technology Embedded English teaching models to create better English classes for students.