Cycloaddition Reactions in Organic Synthesis by Shū Kobayashi, Karl Anker Jorgensen

By Shū Kobayashi, Karl Anker Jorgensen

Cycloaddition reactions are one of the most vital instruments for synthesis in natural chemistry, because those reactions are very important to the fashionable synthesis of ordinary items and biologically lively components. steel catalysis performs an more and more very important function in those reactions, usually permitting numerous stereocenters to be selectively created and built-in within the aim molecules. Kobayashi and Jorgensen's guide presents a variety of examples of metal-catalyzed reactions, together with [2+1], [3+2] and [4+2] cycloadditions. vital reactions corresponding to carbo- and hetero-Diels-Alder, carbocyclic, cyclopropanation and 1,3-dipolar cycloaddition reactions are mentioned. a great number of experimental systems provides a concrete suggestion of using metal-catalyzed cycloaddition reactions in glossy synthesis. The e-book is aimed toward chemists in or academia, who are looking to successfully use cycloadditions of their paintings.

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71). The crucial finding was that the absence of molecular sieves is essential for high enantioselectivity, whereas their presence is necessary for the formation of the chiral titanium catalyst from BINOL and TiCl2(O-i-Pr)2. In the presence of molecular sieves, however, the DielsAlder cycloadduct was obtained in only 9% ee. The molecular sieves-free BINOLTiCl2(O-i-Pr)2 complex, which was prepared by centrifugation of the suspension and decanting, gave cycloadducts in high optical purity which are useful chiral building blocks for the synthesis of anthracyclines and tetracyclines.

A. Evans, J. S. Johnson, Diels-Alder Reaction, in: Comprehensive Asymmetric Catalysis, Vol. III, E. N. Jacobsen, A. Pfaltz, H. Yamamoto (Eds), Springer, New York, 1999, p 1177; (b) H. B. Kagan, O. Riant, Chem. Rev. 1992, 92, 1007; (c) K. Narasaka, Synthesis 1991, 1; (d) K. Maruoka, H. Yamamoto, Asymmetric Reactions with Chiral Lewis Acid Cata- lysts, in: Catalytic Asymmetric Synthesis, I. ), VCH, New York, 1993, p 413; (e) R. Noyori, Asymmetric Catalysis, in: Organic Synthesis, John Wiley and Sons, New York, 1994, p 212.

Another noteworthy feature of the titanium catalyst 10 is that the enantioselectivity is not greatly influenced by reaction temperature (96% ee at –78 8C, 92% ee at –20 8C, 88% ee at 0 8C in the reaction of acrolein and cyclopentadiene). This is unusual for metal-catalyzed asymmetric reactions, with only few similar examples. The titanium catalyst 10 acts as a suitable chiral template for the conformational fixing of a,b-unsaturated aldehydes, thereby enabling efficient enantioface recognition, irrespective of temperature.

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