Christophe Crévisy

From allylic alcohols to aldols via a novel, tandem isomerization–condensation catalyzed by Fe(CO)5

Allylic alcohols react with aldehydes, in the presence of catalytic amounts of Fe(CO)5 and under irradiation, to give mainly aldol products. A small amount of ketone resulting from the classical isomerization process is also isolated. This new aldol-type reaction is a complete atom economy process occurring under neutral conditions.

Enantioselective 1,6-Conjugate Addition to Cyclic Dienones Catalyzed by the Cu−DiPPAM Complex

In the presence of a Cu/DiPPAM catalytic system, various diorganozinc reagents realize 1,6-asymmetric conjugate addition on various cyclic five- and six-membered cyclic dienones, with complete regioselectivity and high ees (93-99%).

A tandem allylic alcohol isomerization–aldol condensation catalyzed by Rh and Ru complexes

Abstract Allylic alcohols react with aldehydes, in an atom economy aldol-type reaction, in the presence of catalytic amounts of various rhodium and ruthenium complexes. This reaction occurs with total regiocontrol under mild conditions, but varying amounts of ketone derived from the competing isomerization reaction are also observed.

Multicomponent Synthesis of Unsymmetrical Unsaturated N‐Heterocyclic Carbene Precursors and Their Related Transition‐Metal Complexes

A low-cost, modular, and easily scalable multicomponent procedure affording access in good yields and excellent selectivity (up to 93%) to a wide range of (a)chiral unsymmetrical 1-aryl-3-cycloalkyl-imidazolium salts is disclosed. Electronic and steric properties of the corresponding unsymmetrical unsaturated N-heterocyclic carbene (U2-NHC) ligands were evaluated and evidenced strong electron donor ability, high steric discrimination, and modular steric demand.

A Fast‐Initiating Ionically Tagged Ruthenium Complex: A Robust Supported Pre‐catalyst for Batch‐Process and Continuous‐Flow Olefin Metathesis

In this study, a new pyridinium-tagged Ru complex was designed and anchored onto sulfonated silica, thereby forming a robust and highly active supported olefin-metathesis pre-catalyst for applications under batch and continuous-flow conditions. The involvement of an oxazine-benzylidene ligand allowed the reactivity of the formed Ru pre-catalyst to be efficiently controlled through both steric and electronic activation. The oxazine scaffold facilitated the introduction of the pyridinium tag, thereby affording the corresponding cationic pre-catalyst in good yield. Excellent activities in ring-closing (RCM), cross (CM), and enyne metathesis were observed with only 0.5 mol % loading of the pre-catalyst. When this powerful pre-catalyst was immobilized onto a silica-based cationic-exchange resin, a versatile catalytically active material for batch reactions was generated that also served as fixed-bed material for flow reactors. This system could be reused at 1 mol % loading to afford metathesis products in high purity with very low ruthenium contamination under batch conditions (below 5 ppm). Scavenging procedures for both batch and flow processes were conducted, which led to a lowering of the ruthenium content to as little as one tenth of the original values.

Development of new iron catalysts for the tandem isomerization–aldol condensation of allylic alcohols

Abstract (bda)Fe(CO) 3 and (COT)Fe(CO) 3 are shown to be excellent catalysts for the tandem isomerization–aldol reaction of allylic alcohols with aldehydes and to significantly increase the scope of this aldolization process, especially, in the case of sterically hindered aldehydes.

Significant Asymmetric Amplification in Enantioselective Cu/DiPPAM-catalyzed 1,6- and 1,4-Conjugate Additions of Diethylzinc to (Di)enones

An unprecedented and strong positive nonlinear effect (NLE) was observed in Cu/DiPPAM-catalyzed asymmetric 1,6-conjugate addition of Et2Zn on (E)-3-(prop-1-en-1-yl)cyclohex-2-enone (71% ee reached with a 40% ee ligand). Moreover, similar behaviors were observed in Cu/DiPPAM-catalyzed 1,4-asymmetric conjugate additions of Et2Zn on both cyclohexenone and (E)-3-non-3-en-2-one (83% and 70% ee, respectively, reached with a 40% ee ligand).

Enantioselective 1,6-conjugate addition of dialkylzinc reagents to acyclic dienones catalyzed by Cu-DiPPAM complex-extension to asymmetric sequential 1,6/1,4-conjugate addition.

CC coupling: DiPPAM 1 and BINAP 2 ligands led to divergent behaviors in the asymmetric conjugate addition (ACA) of dialkylzinc reagents to linear aryldienones, which were applied to the development of a highly selective sequential asymmetric 1,6/1,4-ACA process (see scheme; Tf = triflate, DBU = 1,8-diazabicyclo[5.4.0]undec-7-ene).

Synthesis and Functionalization of New Tropanes Designed for Use as Scaffolds in Combinatorial Chemistry

The [4+3] cycloaddition reaction between alkyloxycarbonyl-substituted pyrroles and α,α′-dibromo ketones in the presence of diethylzinc has been extended to a wide range of substrates. The functionalization of the resulting tropanes has been studied. It is demonstrated that such tropanes represent potentially useful scaffolds.

Multicomponent Synthesis of Chiral Bidentate Unsymmetrical Unsaturated N‐Heterocyclic Carbenes: Copper‐Catalyzed Asymmetric CC Bond Formation

A multicomponent strategy was applied to the synthesis of chiral bidentate unsaturated hydroxyalkyl- and carboxyalkyl-N-heterocyclic carbene (NHC) precursors. The newly developed low-cost chiral ligands derived from amino alcohols and amino acids were evaluated in copper-catalyzed asymmetric conjugated addition and asymmetric allylic alkylation, which afforded the desired tertiary and quaternary carbon stereocenters with excellent regio- and enantioselectivities (up to 99:1 e.r.).