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The title ligand is synthesized and its utility for Rh-catalyzed asymmetric hydrogenations as well as for the alkoxycyclization of enyne (V) is demonstrated.

The first organocatalytic, stereoselective and direct aldol reaction of activated thioesters with aldehydes has been accomplished. The trichlorosilyl ketene thioacetal generated in situ by adding a tertiary amine to a trifluoroethyl thioester in the presence of tetrachlorosilane is activated by catalytic amounts of an enantiomerically pure biheteroaromatic phosphine oxide to react with different aldehydes, coordinated to as well as activated by the chiral cationic hypervalent silicon species. Starting from a variety of readily available thioesters, this Lewis acid-mediated Lewis base-catalyzed transformation allows the direct synthesis of syn-β-hydroxy thioesters in up to 95% ee.

The rearrangements of a few cyclic phenylhydrazones structurally related to 1-phenyl-Δ2-pyrazoline, 1-phenyl-1,4,5,6-tetra hydropyridazine, and 1-phenyl-4,5,6,7-tetrahydro-1,2-diazepine in hot polyphosphoric acid (PPA) are described. The five-membered-ring substrates (the pyrazolines) did not undergo the [3,3] sigmatropic rearrangement typical of the Fischer indolization, the main reaction course being homolytic N–N bond cleavage, leading to benzidine and its 4-(2-benzoylethyl)-4′-(3-phenyl-Δ2-pyrazolin-1-yl) derivative. The six-membered heterocycles underwent two different reactions, both evolving the tautomeric enehydrazine form: the first one is the [3,3] sigmatropic rearrangement, expected for open-chain hydrazones, affording 4-acyl-1,2,3,4-tetrahydroquinoline derivatives; the second one is a retro-Diels–Alder reaction producing methyleneaniline and α,β-unsaturated carbonyl, compounds. The seven -membered -ring substrate gave a 5-acyltetrahydrobenz[b]azepine, resulting from the [3,3] rearrangement, together with both a pyrrolidine and a pyrazine by-product; their formation involves homolytic N–N bond cleavage of the ring, a δ hydrogen abstraction, followed by intramolecular or intermolecular ring closure. Chemical proofs are given for the new structures.

A model which makes use of the complete perturbation treatment of Salem and Devaquet has already been applied to Diels–Alder reactions and is now proposed for the interpretation of regioselectivity in the 1,3-dipolar cycloadditions of 3,5-dichloro-2,4,6-trimethylbenzonitrile oxide with some heteroaromatic systems. The van der Waals minima relevant to the hypothesized alternative reaction paths have been suggested as model structures (perturbed states) for the corresponding weakly interacting complexes in the early stages of the reaction. To evaluate the atom–atom non-bonded interactions between polar partners an explicit Coulombic term is added to the Lennard-Jones (6–12) function previously used. Moreover, because of the dominant contribution of non-interacting atoms in determining the van der Waals minima, the minimization procedure is constrained to the region of the non-bonding energy hypersurface where the 2pπ-orbitals involved in the new bond formation overlap significantly. The obtained regioselectivities are in good agreement with experimental ones.

The reaction of the N-benzylamides of N-heterocyclic carboxylic acids 3 and 6–9 with phosphorus pentachloride affords heterocondensed imidazoles 4 and 10–14 by a scheme reminiscent of Wallach's imidazole synthesis starting from N.N′-dialkyloxamides. Kinetic and labelling experiments are described which support a mechanism involving nitrite ylide species and allow a better understanding of the Wallach reaction. The limiting parameter for the formation of heteroanellated imidazoles is the electron availability of the heterocyclic ring.

The synthesis and application of three examples of a new class of chiral (C2) atropisomeric diphosphines characterized by two interconnected five-membered heteroaromatic rings, with hindered rotation around the interanular bond, are described. Optically pure (+)- and (−)-2,2‘-bis(diphenylphosphino)-4,4‘,6,6‘-tetramethyl-3,3‘-bibenzo[b]thiophene (tetraMe-bitianp) (1a) and the parent unsubstituted system (+)- and (−)-bitianp (1b) were synthesized. They were found to be optically stable at 100 °C and were successfully employed as ligands in the Ru(II)-catalyzed hydrogenation of α- and β-oxo esters to the corresponding α- and β-hydroxy esters and in the hydrogenation of olefinic substrates. The optical and chemical yields were comparable with those reported for the same Ru(II)-binap-catalyzed reactions carried out under the same experimental conditions. The 2,2‘-bis(diphenylphosphino)-3,3‘-bibenzo[b]furan (1c), the oxygenated analogue of bitianp, was found to be configurationally unstable at room temperature....

Two new chiral atropisomeric biheteroaromatic diphosphines are described: 2,2′-bis(diphenylphosphino)-1,1′-bibenzimidazole (3a) and 3,3′-dimethyl-1,1′-bis(diphenylphosphino)-2,2′-biindole (4a). Structural characterization is given and configurational stability at room temperature demonstrated. The oxidation potential was recognized as a good tool to evaluate the electronic availability of the phosphorus atom in the series of biheteroaromatic diphosphines. Its value increases parallel to the electronic demand of the heterocyclic system and also depends on the position of the diphenylphosphino group.

Enantiomerically pure biheteroaromatic diphosphine oxides were synthesised and tested as organocatalysts in two different reactions involving trichlorosilyl compounds. The allylation of aldehydes with allyl(trichloro)silane afforded homoallylic alcohols in fair to good yields and up to 95% ee. Preliminary experiments showed that this new class of metal-free catalysts was able also to promote the stilbene oxide opening by addition of tetrachlorosilane with enantioselectivity higher than 80%. The interesting results in terms of chemical and stereochemical efficiency open the way to further studies towards the development of new chiral heteroaromatic Lewis bases as efficient metal-free catalysts.

Racemic (±)-3,3‘-bis(diphenylphosphinyl)-1,1‘-dimethyl-2,2‘-biindole (1c) (N-Me-2-BINPO) and (±)-3,3‘-bis(diphenylphosphinyl)-1,1‘-bis(methoxymethyl)-2,2‘-biindole (1d) (N-MOM-2-BINPO) were synthesized in satisfactory yields following a three-step reaction sequence, starting from indole. Resolution of racemic 1c and 1d was achieved through fractional crystallization of their diastereomeric adducts with optically active dibenzoyl tartaric acids, followed by alkaline decomplexation of the diastereomerically pure salts. Their trichlorosilane reduction gave enantiopure phosphines (+)- and (−)-(1a) (N-Me-2-BINP) and (+)- and (−)-(1b) (N-MOM-2-BINP). The electrochemical oxidative potential of 1a and 1b was found to be 0.52 and 0.60 V, respectively. Both the enantiomers of (1a) were tested as ligands of Ru(II) in asymmetric hydrogenation reactions of α- and β-oxoesters. Reactions were found to be outstandingly fast and enantioselection quite good. Comparative kinetic experiments on the hydrogenation reaction of ...

Syntheses d'oxazine-1,3ones-6 par reaction de 2H-isoxazolones-5 avec l'α,α-dichlorotoluene, le β,β-dibromo styrene ou la dichloro-2,2 acetophenone

Synthese par cyclisation d'esters d'aryle des acides pyruvohydrazoniques et thiopyruvohydrazoniques et de arylamides d'acides pyruvohydrazoniques avec l'acide polyphosphorique