Matthieu Jouffroy

Confining Phosphanes Derived from Cyclodextrins for Efficient Regio- and Enantioselective Hydroformylation**

Two confining phosphane ligands derived from either α- or β-cyclodextrin produce singly P(III) -ligated metal complexes with unusual coordination spheres. High-pressure NMR studies have revealed that rhodium hydride complexes of the same type are also formed under hydroformylation conditions. This unique feature strongly favors the formation of the branched aldehyde at the expense of the linear one with high enantioselectivity in the rhodium-catalyzed hydroformylation of styrene.

Regioselective Double Capping of Cyclodextrin Scaffolds

Four different regioselective double capping reactions were applied either to α- or β-cyclodextrin (CD) scaffolds. The first, which relied on the use of a rigid, bulky dialkylating reagent containing two trityl-like subunits, gave access to an A,B,D,E-tetrafunctionalised β-CD regioisomer in large scale reactions. Two further capping reactions, involving the dianions PhP(2-) and S(2- , led to the synthesis of new C(1)-symmetrical β-cyclodextrins in which pairs of neighbouring glucose units are linked by very short spacers. The last double capping reaction described allowed the high-yield preparation of unprecedented α- and β-cyclodextrins containing two sulfate handles. Proximal capping turned out to be favoured for each of the above difunctional reagents. The structural characterisation of the capped species was achieved by thorough NMR investigations as well as by single-crystal X-ray diffraction studies.

Regioselective opening of proximally sulfato-capped cyclodextrins.

Sulfato groups capping one or two pairs of adjacent glucose units in methylated cyclodextrin (CD) derivatives have been found to undergo regioselective opening with various nucleophiles; the reported methodology opens the way to the efficient synthesis of tridifferentiated α- and β-cyclodextrins that constitute key starting materials for the preparation of heteropolydentate cavitands.

Phosphinocyclodextrins as confining units for catalytic metal centres. Applications to carbon–carbon bond forming reactions

Summary The capacity of two cavity-shaped ligands, HUGPHOS-1 and HUGPHOS-2, to generate exclusively singly phosphorus-ligated complexes, in which the cyclodextrin cavity tightly wraps around the metal centre, was explored with a number of late transition metal cations. Both cyclodextrin-derived ligands were assessed in palladium-catalysed Mizoroki–Heck coupling reactions between aryl bromides and styrene on one hand, and the rhodium-catalysed asymmetric hydroformylation of styrene on the other hand. The inability of both chiral ligands to form standard bis(phosphine) complexes under catalytic conditions was established by high-pressure NMR studies and shown to have a deep impact on the two carbon–carbon bond forming reactions both in terms of activity and selectivity. For example, when used as ligands in the rhodium-catalysed hydroformylation of styrene, they lead to both high isoselectivity and high enantioselectivity. In the study dealing with the Mizoroki–Heck reactions, comparative tests were carried out with WIDEPHOS, a diphosphine analogue of HUGPHOS-2.

Regioselective di- and tetra-functionalisation of γ-cyclodextrin using capping methodology

Alkylation of γ-cyclodextrin with 3 equiv. of 1,3-bis[bis(4-tert-butylphenyl)chloromethyl]benzene, followed by permethylation afforded selectively a singly capped (A,B), as well as two doubly capped (A,B:D,E and A,B:E,F) methylated γ-CDs. Deprotection with HBF4 gave quantitatively the corresponding diols and tetrols, which constitute valuable starting compounds for further functionalisation.

Synthesis of Optically Active Polystyrene Catalyzed by Monophosphine Pd Complexes

Cationic Pd(II) monophosphine complexes derived from α- and β-cyclodextrins (CDs) promote the homopolymerization of styrene under carbon monoxide pressure. Although reversible CO coordination takes place under catalytic conditions according to (13) C NMR studies with (13) C-enriched CO, both complexes catalyze the formation of CO-free styrene polymers. These macromolecules display optical activity as a result of the presence of stereoregular sequences within the overall atactic polymer.

Capping Methodology in Cyclodextrin Chemistry: Use of a Symmetrical Diketone Reagent for Regiospecific Installation of Unsymmetrical Imine–Enamine and Imidazole Caps

Methylated α- and β-cyclodextrin skeletons were both equipped with an unsymmetrical N-(2-N-alkylaminoacenaphthenyl)alkylimine rigid handle. The capping reaction, which consists of condensing a diaminocyclodextrin with highly symmetrical acenaphthenequinone, was found to be regiospecific when starting from cyclodextrin-diamines without any symmetry element. All modified cyclooligosaccharides have intra-annular nitrogen donor atoms. They undergo further cyclization on oxidation, whether chemically with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone or electrochemically, to give highly strained cyclodextrins capped with an unsymmetrical 1,2-disubstituted 1H-imidazole unit.