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294ChemInform Abstract The synthesis of the title compound (I) and of some analogues is described in a 23-step sequence starting from (I). The various difficulties of the synthesis and several blind alleys that have been followed are discussed in detail.

The new axially dissymmetric diphosphines (R)-and (S)-(6,6-dimethoxybiphenyl-2,2'-diyl)bis(diphenyl phosphine) ((R)-and ( S p a ; 'MeO-BIPHEP) and the analogues (R)-and (S)-Sb and Sc have been synthesized in enantiomerically pure form. These ligands have become readily available by a synthetic scheme which employs, as key steps, an ortho-lithiation/iodination reaction of the (m-methoxypheny1)diphenylphosphine oxides 8 and a subsequent Ullmunn reaction of the resulting iodides 9 to provide the racemic bis(phosphine oxides) 10. The bis(phosphine oxides) 10 subsequently are resolved with (-)-(2R,3R)-and (+)-(2S,3S)-0-2,3-dibenzoyltartaric acid and reduced to diphosphines 5. The Ullmann reaction constitutes a new and efficient route to 2,2'-bis(phosphinoy1)-substituted biphenyl systems. Absolute configurations were established for (R)-Sa by X-ray analysis of the derived Pd complex (R,R)-17a, and for Sb and 5c by means of 'H-NMR comparisons of the derived Pd complexes 16 or 17, respectively, and by means of CD comparisons. The MeO-BIPHEP diphosphine 5a proved to be as efficient as the previously described BIPHEMP diphosphine ((6,6'-dimethylbiphenyl-2,2'-diyl)bis(diphenylphosphine)) in enantioselective isomerizations and hydrogenations.1. Introduction. -The potential of axially dissymmetric diphosphines such as the prototype compound BINAP (1) as asymmetry-inducing ligands has been amply demonstrated for various transition-metal-catalyzed reactions, in particular for Rh'-and RUT'-catalyzed hydrogenations [ 11. Therefore, it is not surprising that considerable efforts have been undertaken for the design and synthesis of other atropisomeric diphosphine ligands. Some time ago, the parent compound in the atropisomeric biphenyl series, the BIPHEMP ligand 2a has been synthesized by us [2] as well as independently by Freyd and coworkers [3], and by Miyashita et al. [4]. Moreover, the substituted analogues 2b, 2c, and the bridged analogue 3 have also been synthesized [2]. The BIPHEMP ligand was shown to be at least as efficient as the BINAP ligand in Rhl-catalyzed allylamine-to-enamine isomerizations [2] and in Ru"-catalyzed hydrogenations of allylic alcohols and P-keto

ChemInform Abstract The hematoporphyrin-sensitized photoreaction of the aromatic retinoid (I) using light with λ ≥ 400 nm yields the cyclodimers (II) (space group P21/a, Z=4) and (III) (P1, Z=2). Using shorter wavelengths, additionally two dimers with a Z-configurated side-chain are obtained.

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