Olivier Riant

Asymmetric Diels-Alder Reaction Catalysed by some Chiral Lewis Acid

Diels-Alder reaction between cyclopentadiene and various dienophiles (mainly methacrolein) at −78°C was catalysed by various chiral aluminum alcoholates. The catalysts were prepared by reaction of EtAlCl2 with several families of diol (or their monoether monoalcohol derivatives). The most enantioselective catalyst is derived from diol 5a. A detailed investigation in that case gives some light on the experimental parameters of the system, especially the reproductible preparation of the catalyst. Enantiomeric excess up to 86% (in exo cycloadduct 2a) could be achieved. Tentative structures are proposed for the transition state of the reaction.

Asymmetric Diels-Alder reaction catalyzed by chiral bases☆

Anthrone has been found to react with N-methyl maleimide in the presence of catalytic amounts of various chiral β-amino alcohols. The optically active cycloadduct 3a has been obtained in excellent yield. Several features of the reaction have been studied. Anthrone 1 has been found to react with N-substituted maleimides 2 in presence of catalytic amounts of various chiral β-aminoalcohols (ee up to 60%).

A New Class of Ferrocene-Based l,2-Bis(phosphanes) Possessing only Planar Chirality

Chiral 1,2-bis(phosphanes) 13, devoid of individual chiral centers, have been prepared in three steps from chiral sulfoxide 10. Their corresponding rhodium complexes were used as catalysts for asymmetric hydrogenation, giving high ee values (⩽ 95%) in the reduction of itaconic acid or its ester. A cationic rhodium complex involving coordination of two molecules of 13b and one molecule of oxygen has been isolated and its crystal structure established.

Asymmetric Base-catalyzed Cycloaddition Between Anthrone and some Dienophiles

Anthrone has been found to react with N-methylmaleimide in the presence of catalytic amounts of various chiral β-aminoalcohols. The cycloadduct 3a has been obtained in excellent yield with enantiomeric excess of up to 61%. Its absolute configuration has been assigned by X-ray crystallography. Several features of the reaction have been studied: variation of dienophile; competition between cycloaddition and formation of the optically active Michael adduct 4; solvent and temperature effects. Mechanistic studies are in agreement with a concerted [4+2] process, providing an unique case of a base-catalyzed asymmetric Diels-Alder reaction. Anthrone with N-methylmaleimide in presence of various β-aminoalcohols to give 3a. Several features of this base-catalyzed Diels-Alder reaction have been studied. Quinidine leads to optically active 3a (ee up to 61%) whose absolute configuration has been established.

Synthesis of Chiral Carbocations Linked to a Ferrocene Unit

Orthosubstituted ferrocene carboxaldehydes (100% ee) were transformed into carbinols by addition of a Grignard reagent. Treatment by strong acids (HPF6, CF3SO3H, etc) gave isolated chiral carbocations which are good Lewis acid catalysts for various reactions such as Diels-Alder reaction. Chiral carbocations linked to a planary chiral ferrocene unit were prepared starting from enantiopure α-substituted ferrocene aldehydes.

TOWARDS NEW FERROCENYL LIGANDS FOR ASYMMETRIC CATALYSIS

Some new approaches for asymmetric synthesis of chiral femenyl ligands are described. Many types of ferrocene compounds with planar chirality were prepared through diastereoselective ortholithiation, thanks to a chiral sulfoxide or chiral aced auxiliary. Various mono- and diphosphines may be subsequently generated. In the sulfoxide route, a key intermediate is pure monolithioferrocene. A convenient procedure was set up, involving the isolation of stable tri-n-butylstannyl-femene as a precursor of monolithioferrocene. The species FczPH (Fc = ferrocenyl) and its borane protected derivative allowed to synthesize chiral diphosphines where the usual PPh2 groups are replaced by the PFc2 fragment.

Asymmetric Synthesis of Chiral Ferrocenyl Fulleropyrrolidines as Potential Building Blocks for New Materials

Asymmetric [3+2] cycloaddition of chiral ferrocenyl substituted azomethine ylides to C60 leads to the corresponding fulleropyrrolidines with high diastereoselectivities. This methodology has been applied to the preparation of a C2-symmetric enantiopure fullerene dimer.

Design of a Genetic Algorithm for the Simulated Evolution of a Library of Asymmetric Transfer Hydrogenation Catalysts

A library of catalysts was designed for asymmetric-hydrogen transfer to acetophenone. At first, the whole library was submitted to evaluation using high-throughput experiments (HTE). The catalysts were listed in ascending order, with respect to their performance, and best catalysts were identified. In the second step, various simulated evolution experiments, based on a genetic algorithm, were applied to this library. A small part of the library, called the mother generation (G0), thus evolved from generation to generation. The goal was to use our collection of HTE data to adjust the parameters of the genetic algorithm, in order to obtain a maximum of the best catalysts within a minimal number of generations. It was namely found that simulated evolutions results depended on the selection of G0 and that a random G0 should be preferred. We also demonstrated that it was possible to get 5 to 6 of the ten best catalysts while investigating only 10 % of the library. Moreover, we developed a double algorithm making this result still achievable if the evolution started with one of the worst G0.

New efficient copper fluoride-based catalyst for enantioselective hydrosilylation of ketones in aerobic conditions

A new copper(II) fluoride-chiral diphosphines catalytic system was developed. This one is very efficient and selective for the hydrosilylation of several substituted or unsubstituted aromatic ketones in so far as moderate to excellent enantioselectivities were obtained. An oxygen acceleration effect was observed that led us to propose a practical protocol with a low amount of catalyst.

Synthesis of poly-ferrocene heterocycles by cycloaddition of mono- or bis(ferrocenecarbonyl)acetylenes and bis[1,2]dithiolo[1,4]thiazinethiones

Cycloaddition of a bis[1,2]dithiolo[1,4]thiazine ketothione and mono- or bis(ferrocenecarbonyl)acetylenes under catalysis by scandium triflate gave mono- and bis-ferrocenecarbonyl-1,3-dithiolylidene[1,2]dithiolo[1,4]thiazines. Cycloaddition of a bis-dithiolothiazine dithione and bis-ferrocenylbutynedione gave 3,5-di(bis-ferrocenecarbonyl-1,3-dithiolylidene)[1,4]thiazine, a structure related to extended tetrathiafulvalenes