Metal-Catalyzed Cycloisomerization Cascades

An intermolecular version, involving allenamide and acyclic diene partners, has also been developed [28]. Thus, Vincente and coworkers used this reactivity toward the synthesis of functionalized tetrahydrocarbazole derivatives, by a 

4 Miscellaneous Gold- and Iron-Catalyzed Cascade Reactions The car-benic reactivity of gold catalysis was exploited toward the synthesis of stereoselective six-membered ring carbocycles, through cyclopropanation reactions incorporated in cascade sequences [31]. 

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With a cascade process in mind, Chen envisaged a transition metal-catalyzed cycloisomerization reaction. 

Abstract This review gives an insight into the growing field of transition metal-catalyzed cascades. More particularly, we have focused on the construction of complex molecules from acyclic precursors. Several approaches have been devised. We have not covered palladium-mediated cyclizations, multiple Heck reactions, or ruthenium-catalyzed metathesis reactions because they are discussed in others chapters of this book. This manuscript is composed of two main parts. In the first part, we emphasize cascade sequences involving cycloaddition, cycloisomerization, or ene-type reactions. Most of these reaction sequences involve a transition metal-catalyzed step that is either followed by another reaction promoted by the same catalyst or by a purely thermal reaction. A simple change in the temperature of the reaction mixture is often the only technical requirement to go from one step to another. The second part covers the cascades relying on transition metalo carbenoid intermediates, which have recently undergone tremendous... 

Aiming for the development of transition metal-catalyzed protocols, which would allow a regioselective synthesis of C2-substituted indolizine cores, Gevorgyan reported a highly efficient Au(III)-catalyzed cascade cycloisomerization of skipped propargylpyridines 346 into indolizines 347 (Scheme 9.119) [299,300]. This cascade transformation involved a facile 1,2-migration of silyl-, stannyl-, and even germyl... 

Recent advances in the cyclizations catalyzed by transition metals and their complexes are reviewed. The catalytic cyclizations discussed here include various carbocyclizations, for example, cycloisomerization, cycloaddition, reductive cyclization, and so on cascade carbocyclizations, for example, cyclotrimerization, silylcarbocyclization, and Heck reaction carbonylative carbocyclizations cyclohy-drocarbonylations intramolecular hydrosilylations intramolecular silylformyla-tions and aldol cyclizations. These reactions serve as efficient and useful methods for the syntheses of a variety of heterocycles and carbocycles that are important... 

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