Das Programm ACE 1.0 (ACE steht für „asymmetric catalyst evaluation“) sagt schnell und sicher das stereochemische Ergebnis asymmetrischer Reaktionen voraus. Die Genauigkeit von ACE wird anhand asymmetrischer Diels-Alder-Cycloadditionen und organokatalytischer Aldolreaktionen demonstriert (siehe Bild; R = iPr (2 a), Me (2 b), Ph (2 c)).
[Show abstract][Hide abstract] ABSTRACT: Most organic and organometallic catalysts have been discovered through serendipity or trial and error, rather than by rational design. Computational methods, however, are rapidly becoming a versatile tool for understanding and predicting the roles of such catalysts in asymmetric reactions. Such methods should now be regarded as a first line of attack in the design of catalysts.
[Show abstract][Hide abstract] ABSTRACT: A review. Reaction of 2-phenylacetaldehyde with the Me3Si ether of diphenyl-prolinol, with removal of H2O, gives a cryst. enamine (I). The HBF4 salts of the MePh2Si ether of diphenyl-prolinol and of 2-(tert-butyl)-3-methyl- and 5-benzyl-2,2,3-trimethyl-1,3-imidazolidin-4-one react with cinnamaldehyde to give cryst. iminium salts II, III, and IV. Single crystals of the enamine and of two iminium salts, II and III, were subjected to x-ray structure anal., and a 2-dimensional-NMR spectrum of the third iminium salt was recorded. The crystal and NMR structures confirm the commonly accepted, general structures of the two types of reactive intermediates in organocatalysis with the five-membered heterocycles, i.e., V, VI. Fine details of the crystal structures are discussed in view of the obsd. stereoselectivities of the corresponding reactions with electrophiles and nucleophiles. The structures I and II are compared with those of other diphenyl-prolinol derivs. (from the Cambridge File CSD) and discussed in connection with other reagents and ligands, contg. geminal diaryl groups and being used in enantioselective synthesis. The iminium ions III and IV are compared with N-acylated imidazolidinones VII and VIII, and common structural aspects such as minimization of 1,5-repulsion (the A1,3-effect), are discussed. The crystal structures of the simple diphenyl-prolinol.HBF4 salt and of Boc- and benzoyl-(tert-butyl)methyl-imidazolidinone (Boc-BMI and Bz-BMI, resp.) are also reported. Finally, the crystal structures are compared with previously published theor. structures, which were obtained from high-level-of-theory DFT calcns. Delicate details including pyramidalization of trigonal N-atoms, distortions around iminium C=N bonds, shielding of diastereotopic faces, and the pi-interaction between a benzene ring and a Me group match so well with, and were actually predicting the exptl. results that the question may seem appropriate, whether one will soon start considering to carry out such calcns. before going to the lab. for exptl. optimizations.
[Show abstract][Hide abstract] ABSTRACT: Herein we report the first fully quantum mechanical study of enantioselectivity for a large data set. We show that transition state modeling at the UB3LYP-DFT/6-31G* level of theory can accurately model enantioselectivity for various dioxirane-catalyzed asymmetric epoxidations. All the synthetically useful high selectivities are successfully "predicted" by this method. Our results hint at the utility of this method to further model other asymmetric reactions and facilitate the discovery process for the experimental organic chemist. Our work suggests the possibility of using computational methods not simply to explain organic phenomena, but also to predict them quantitatively.
Journal of the American Chemical Society 03/2009; 131(11):3965-73. DOI:10.1021/ja806951r · 12.11 Impact Factor
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