title: New Class of Chiral Diphosphine Ligands for Highly Efficient Transition Metal-Catalyzed Stereoselective Reactions: The Bis(diphenylphosphino) Five-membered Biheteroaryls.
abstract: The synthesis and application of three examples of a new class of chiral (C(2)) 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 degrees C and were successfully employed as ligands in the Ru(II)-catalyzed hydrogenation of alpha- and beta-oxo esters to the corresponding alpha- and beta-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. Complete structural X-ray elucidation of the Pd complexes of 1a-c is reported. The advantages of these biheteroaromatic ligands over the classical biaryl systems are discussed.
authors.affiliation: Dipartimento di Chimica Organica e Industriale, Università di Milano, e Centro CNR Sintesi Stereochimica Speciali Sistemi Organici, Via Golgi 19, I-20133 Milano, Italy, Dipartimento di Chimica Inorganica, Metallorganica e Analitica Università di Milano, e Centro CNR Sintesi e Struttura dei Composti dei Metalli di Transizione nei Bassi Stati di Ossidazione, Via Venezian 21, I-20133 Milano, Italy, Dipartimento di Chimica Strutturale e Stereochimica Inorganica, Università di Milano, Via Venezian 21, I-20133 Milano, Italy, and Centro CNR per lo Studio delle Relazioni fra Struttura e Reattività Chimica, Via Golgi 19, I-20133 Milano, Italy.
authors.forename: Tiziana
authors.initials: T
authors.lastname: Benincori
authors.forename: Elisabetta
authors.initials: E
authors.lastname: Brenna
authors.forename: Franco
authors.initials: F
authors.lastname: Sannicolò
authors.forename: Licia
authors.initials: L
authors.lastname: Trimarco
authors.forename: Patrizia
authors.initials: P
authors.lastname: Antognazza
authors.forename: Edoardo
authors.initials: E
authors.lastname: Cesarotti
authors.forename: Francesco
authors.initials: F
authors.lastname: Demartin
authors.forename: Tullio
authors.initials: T
authors.lastname: Pilati