Bull. Chem. Soc. Jpn. への投稿のすすめ

Transition Metal-Catalyzed Carbocyclizations in Organic Synthesis.

ConspectusTransition-metal catalyzed C–H functionalizations became a complementary and efficient bond-forming strategy over the past decade. In this respect, Cp*Rh(III) complexes have emerged as powerful catalysts for a broad spectrum of reactions giving access to synthetically versatile building blocks. Despite their high potential, the corresponding catalytic enantioselective transformations largely lag behind. The targeted transformations require all the remaining three coordination sites of the central rhodium atom of the catalyst. In consequence, the chiral information on a competent catalyst can only by stored in the cyclopentadienyl unit. The lack of suitable enabling chiral cyclopentadienyl (Cpx) ligands is the key hurdle preventing the development of such asymmetric versions. In this respect, an efficient set of chiral Cpx ligands useable with a broad variety of different transition-metals can unlock substantial application potential. This Account provides a description of our developments of two...

Chiral Cyclopentadienyls: Enabling Ligands for Asymmetric Rh(III)-Catalyzed C–H Functionalizations

This work was supported by the Foundation for Science and Technology (FCT), Portugal (projects PTDC/QUI-QUI/113687/2009 and PEst-C/QUI/UI0081/2013). A.G. (SFRH/BD/43531/2008) and M.J.M. (SFRH/BD/61262/2009) thank FCT for grants.

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Chromone: A Valid Scaffold in Medicinal Chemistry

On the basis of Kohn–Sham density functional (DFT) investigations on elementary organic and organometallic reactions, we show how a detailed understanding of the electronic structure of a reaction system can help recognize certain characteristics of the process, yielding valuable mechanistic concepts. The concept of the base as a selective catalyst in E2 eliminations, for example, leads to a straightforward explanation for the general preference for anti over syn stereochemistry in base-induced elimination reactions. Furthermore, electronic structure considerations provide the so-called E2–SN2 mechanistic spectrum, in terms of which one can interpret and understand the competition between elimination and substitution reactions and the shift, on solvation, of the reactivity from E2 to SN2. In addition, mechanistic concepts from organometallic and organic chemistry are linked as we argue that oxidative addition may be conceived, in some respect, as the organometallic analog of the frontside SN2 substitution. Finally, we introduce the ideas of “activation strain” of and “transition state interaction” between the deformed reactants in the activated complex, which together determine the activation energy, ΔE*=ΔE+ΔE. They prove to be helpful conceptual tools for understanding in detail how activation barriers and relative efficiencies of competing reaction mechanisms arise and how they may be affected (e.g., by changing reactants or by solvation). © 1999 John Wiley & Sons, Inc. J Comput Chem 20: 114–128, 1999

Understanding reactivity with Kohn–Sham molecular orbital theory: E2–SN2 mechanistic spectrum and other concepts

Transformations of chiral iron complexes used in organic synthesis. Reactions of .eta.5-CpFe(PPh3)(CO)COCH3 and related species leading to a mild, stereospecific synthesis of .beta.-lactams

The synthesis of title cyclopentadienyl ligand I with C2 symmetry is described. I was designed to maximize the steric encumbrance of both diastereotopic faces, an effect achieved by annelation involving a stereospecifically 1,5-disubstituted bicyclo[2.2.2]octane frame. The system has been complexed to cobalt, titanium, and zirconium as model transition metals to demonstrate its effective function as a ligand in the formation of potentially catalytic organometallic complexes. As an example of this potential, the resulting titanocene dichloride was a catalyst precursor in the enantioselective hydrogenation of 2-phenyl-1-butene and 2-ethyl-1-hexene with unprecedented stereoselectivity.

A designed, enantiomerically pure, fused cyclopentadienyl ligand with C2 symmetry. Synthesis and use in enantioselective titanocene-catalyzed hydrogenations of alkenes

Mark E. Welker

Papers

Transformations of chiral iron complexes used in organic synthesis. Reactions of .eta.5-CpFe(PPh3)(CO)COCH3 and related species leading to a mild, stereospecific synthesis of .beta.-lactams

A designed, enantiomerically pure, fused cyclopentadienyl ligand with C2 symmetry. Synthesis and use in enantioselective titanocene-catalyzed hydrogenations of alkenes

3 + 2 Cycloaddition reactions of transition-metal 2-alkynyl and .eta.1-allyl complexes and their utilization in five-membered-ring compound syntheses

Organocobalt Complexes in Organic Synthesis

Synthesis of Cobalt Substituted 1,3-Diene Complexes with Unusual Structures and Their Exo Selective Diels-Alder Reactions