Die blaßgelben Titelverbindu:ngen (I) und (III) erleiden umkehrbare photochemische konrotatorische elektrocycljsche Reaktionen und liefern in quantitativen Ausb. die dunkelroten bei 100°C stabilen Anhydride (II) bzw. (IV).

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Optically active phosphine ligands, especially C 2 -symmetric diphosphine ligands, have played an important role in various metal-catalyzed asymmetric transformations, and numerous phosphine ligands have been prepared for the development of effective catalytic asymmetric processes. [1] Dramatic results from Knowles and co-workers with the C 2 -symmetric P-chiral ligand 1,2-ethanediylbis[(2-methoxyphenyl)phenylphosphane] (dipamp) for Rh-catalyzed hydrogenations opened up this field of asymmetric catalysis. [2] However, it took nearly two decades for other groups to develop efficient methods to prepare C 2 -symmetric P-chiral diphosphine ligands, largely as a result of the synthetic difficulties in the construction of the P-chiral P centers. [3,4] Nevertheless, some C 2 -symmetric Pchiral diphosphine ligands, such as BisP*, [4a] MiniPhos, [4b] TangPhos, [4c] DiSquareP*, [4d] DuanPhos, [4e] and QuinoxP*, [4f] which exhibit almost perfect enantioselectivity in some Rhcatalyzed asymmetric hydrogenations, have been developed recently. However, a major drawback in many of the requisite synthetic methods (developed by the groups of Imamoto, [3a] JugØ, [3b] Corey, [3c] Evans, [3e] and Livinghouse [3g] ) is that either only one enantiomer of the ligand is readily accessible owing to the nature of the chiral auxiliaries used in the formation of the chiral center or there is a need for tedious diastereomeric derivatization, separation, and deprotection sequences.Ferrocene-based phosphine ligands are well documented. [5] They are more amenable to asymmetric catalysis than many other types of chiral ligands as a result of their easy accessibility and derivatization as well as special electronic and steric properties. Indeed, several families of ferrocenebased phosphine ligands with subtle structural variations have been developed in the last few years. Most of these ligands incorporate both C-centered chirality and planar chirality, and they have proved to be highly effective in numerous asymmetric reactions. In stark contrast, much less attention has been paid to P-chiral phosphines that bear ferrocenyl groups, [3k,l, 5] doubtless as a result of the previous difficulties in their synthesis. Very recently, we reported a highly stereoselective and modular synthesis of ferrocene-based P-chiral phosphine ligands using a simple and straightforward strategy, that is, reaction of a chiral organometallic reagent with a dichlorophosphine, followed by a second organometallic reagent; several families of new ferrocene-based P-chiral phosphine ligands have been developed. [6] Herein, we describe the highly stereoselective synthesis of a new ferrocenebased C 2 -symmetric diphosphine ligand 1 (TriFer). To the best of our knowledge, ligand 1 is the first class of C 2 -symmetric diphosphine that combines C-centered, P-centered, and planar chirality. Most importantly, unprecedented enantioselectivities have been achieved with ligand 1 for the Rhcatalyzed asymmetric hydrogenation of a-substituted cinnamic acids, a class of ver...

A very simple, highly stereoselective and modular synthesis of ferrocene-based P-chiral phosphine ligands has been developed. On the basis of this new methodology, several new families of ferrocene-based phosphine ligands have been prepared coupling chirality at phosphorus with other, more standard stereogenic features. The introduction of P-chirality into ferrocene-based phosphine ligands enhances the enantioselective discrimination produced by the corresponding Rh catalyst when a matching among the planar chirality, carbon chirality, and the chirality of phosphorus is achieved.

Photochromic Heterocyclic Fulgides. Part 4.' The Thermal and Photochemical Reactions of ( E )lsopropyl idene-[a-(2and -(3-t h ienyl)ethyl idene]succinic Anhydrides and Related Compounds