Samuel Claude Constant

Self-adaptable catalysts: substrate-dependent ligand configuration.

Pd(II) allyl and Pd(0) olefin complexes containing the configurationally labile ligand 1,2-bis-[4,5-dihydro-3H-dibenzo[c-e]azepino]ethane were studied as models for intermediates in Pd-catalyzed allylic alkylations. According to NMR and DFT studies, the ligand prefers C(s) conformation in both eta3-1,3-diphenylpropenyl and eta3-cyclohexenyl Pd(II) complexes, whereas in Pd(0) olefin complexes it adopts different conformations in complexes derived from the two types of allyl systems in both solution and, as verified by X-ray crystallography, in the solid state. These results demonstrate that the Pd complex is capable of adapting its structure to the reacting substrate. The different structural preferences also provide an explanation for the behavior of 1,3-diphenyl-2-propenyl acetate and 2-cyclohexenyl acetate in Pd-catalyzed allylic alkylations using pseudo-C2 and pseudo-C(s) symmetric ligands.

Enantio- and regioselective CpRu-catalyzed Carroll rearrangement*

The addition of unstabilized carbonyl nucleophiles to allyl-metal fragments still represents a challenge for generating stereoselectively tertiary (and quaternary) stereogenic centers. In this context, the decarboxylative Carroll rearrangement of secondary and tertiary allyl β-ketoesters is particularly interesting since chiral γ,δ-unsaturated ketones are obtained. Herein, we show that CpRu half-sandwich complexes can, in the presence of selected enantiopure diimine ligands, catalyze this transformation and afford complete conversions and decent level of enantiomeric excess. Zwitterionic adducts of a hexacoordinated phosphorus anion and CpRu moieties were also associated and shown to generate air-, moisture-, and microwave-stable catalysts that can be readily purified and recycled. Carroll rearrangements of allylic β-ketoesters performed with these zwitterionic species occur with better regio- and enantioselectivity.

Asymmetric Synthesis and Configurational Stability of C2-Symmetric Hexacoordinated Phosphate Anions (TARPHATs) with Predetermined Chirality from Tartrate Esters

C2-Symmetric TARPHAT anions 5 made of a central PV atom, one tartrato (=dialkyl 2,3-di(hydroxy-KO)butanedioato(2-)), and two tetrachloropyrocatecholato (=3,4,5,6-tetrachlorobenzene-1,2-diolato(2-)-KO,KO) ligands can be easily prepared in decent to high yields (50-86%) as their dimethylammonium salt by using a one-pot process and simple commercially available starting materials. The presence of the chiral tartrato ligands (usually (2R,3R)) leads to the formation of diastereoisomeric anions ((?,2R,3R)/(?,2R,3R)). Decent to good control by the chiral ligands - under equilibration conditions - over the ? or ? configuration of the adducts was observed (d.r. 84 : 16 in CHCl3 for the di(tert-butyl) tartrate derivative), the selectivity depending on the nature of the ester chains as well as on the solvent.

Mannose derived hexacoordinated phosphate?a generally efficient chiral anion for asymmetric applicationsElectronic supplementary information (ESI) available: spectroscopic and crystallographic data on [Me2NH2][3]. See http://www.rsc.org/suppdata/cc/b3/b305169b/

Mannose derived hexacoordinated phosphate--prepared in two steps from methyl-alpha-D-mannopyranoside--is a chiral anionic auxiliary with broad asymmetric efficiency.

Diversity Oriented Synthesis of Chiral Hexacoordinated Phosphate Anions

Novel hexacoordinated phosphate anions consisting of a central phosphorus(v) atom and at least one tetrachloropyrocatechol ligand can be simply prepared in modest to decent yields (37-71%) as their dimethylammonium salts following a one-pot process and with simple, usually commercially available, starting materials. A variety of symmetrical diones (α-diketones or ortho-quinones) can be used in this protocol and the structurally-diverse products are chemically stable when two tetrachloropyrocatechol ligands surround the P atom.