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A new series of C-1-symmetric P-chirogenic bisphosphine ligands of the type (R)-5,8-Si-Quinox-tBu(3)(Silyl = SiMe3, SiEt3, SiMe2Ph) have been developed. The bulky silyl modulators attached to the ligand backbone fix the phosphine substituents to form rigid chiral environments that can be used for substrate recognition. The ligand showed high performances for a copper(I)-catalyzed asymmetric borylative cyclopropanation of bulky silyl-substituted allylic electrophiles to afford higher disfavored 1,2-cis-silyl-boryl-cyclopropanes than the other possible isomers, trans-cyclopropane and allylboronate (up to 97% yield; 98% ee; cis/trans = >99:1; cyclopropane/allylboronate = >99:1 Detailed computational studies suggested that the highly rigid phosphine conformation, which is virtually undisturbed by the steric interactions with the bulky silyl-substituted allyl electrophiles, is key to the high stereo- and product-selectivities. Furthermore, the detailed computational analysis provided insight into the mechanism of the stereoretention or -inversion of the chiral alkylcopper(I) intermediate in the intramolecular cyclization.

Metal-catalyzed asymmetric synthesis is one of the most important methods for the economical and environmentally benign production of useful optically active compounds. The success of the asymmetric transformations is significantly dependent on the structure and electronic properties of the chiral ligands coordinating to the center metals, and hence the development of highly efficient ligands, especially chiral phosphine ligands, has long been an important research subject in this field. This review article describes the synthesis and applications of P-chiral phosphine ligands possessing chiral centers at the phosphorus atoms. Rationally designed P-chiral phosphine ligands are synthesized by the use of phosphine-boranes as the intermediates. Conformationally rigid and electron-rich P-chiral phosphine ligands exhibit excellent enantioselectivity and high catalytic activity in various transition-metal-catalyzed asymmetric reactions. Recent mechanistic studies of rhodium-catalyzed asymmetric hydrogenation are also described.

Asymmetric hydrogenation of sterically hindered substrates still constitutes a long-standing challenge in the area of asymmetric catalysis. Herein, an efficient palladium acetate (an inexpensive Pd salt with low toxicity) catalyzed asymmetric hydrogenation of sterically hindered N-tosylimines is realized with high catalytic activities (S/C up to 5000) and excellent enantioselectivities (ee up to 99.9%). Quantum chemical calculations suggest that uniformly high enantioselectivities are observed due to the structurally different S- and R-reaction pathways., Sterically hindered unsaturated compounds are challenging substrates for asymmetric hydrogenation. Here, the authors report a palladium/chiral (bis)phosphine catalytic system that hydrogenates a number of hindered N-tosylimines with excellent enantioselectivitites.

P-Stereogenic PNP type pincer iridium complexes PNPtBuMeIrH2Cl (3) and PNPtBuMeIrH3 (4) were synthesized in reasonable yields and characterized by 1H NMR, 13C NMR, 31P NMR, HRMS and/or single crystal X-ray diffraction. The ORTEP diagram shows that the coordination geometry around the iridium center of complex 3 is approximately octahedral. The chlorinated iridium complex (3) and/or the trihydride iridium complex (4) were used as catalysts in the asymmetric hydrogenation of ketones, olefins and quinoline to provide the desired products with up to 17% enantioselectivity.

Herein, we provide evidence showing that the long-held major–minor concept for catalytic asymmetric reactions needs to be readdressed. The asymmetric hydrogenation of enamide 1 catalyzed by the chiral Rh(I) complex of (R,R)-BenzP* quantitatively yields the corresponding hydrogenated R-product 2 with 89.6% ee. The most abundant catalyst–substrate species in the reaction pool was found to be [Rh((R,R)-BenzP*)(Ph(MeCONH)C═CH2)]+SbF6– (5). This species is also the most reactive to hydrogen among the various Rh complexes. Low-temperature hydrogenation experiments showed direct transformation of 5 to 2 with over 98% ee (R). However, the oxidative addition of H2 to 5 would yield the S-product. Computation has now revealed a low-energy R-enantioselective route, whereby H2 addition to 5 is followed by π-bond dissociation, isomerization of nonchelating Rh species, and recoordination of the double bond before C–H bond formation occurs.

The treatment of optically P-chiral tetraphosphine, (3S,6R,9R,12S)-6,9-di-tert-butyl-2,2,3,12,13,13-hexamethyl-3,6,9,12-tetraphosphatetradecane (1), with rhodium(I), palladium(II), and ruthenium(II) complex precursors led to the selective formation of mono-, di-, or trinuclear homo- or heterometallic complexes, [Rh(1)]SbF6 (4), [{Rh(nbd)}2(1)](SbF6)2 (3), [{Pd(η3-allyl)}2(1)](SbF6)2 (5), [{RuCl(η5-C5(CH3)5)}2(1)] (6), and [{RuCl2(η6-benzene)}2(PdCl2)(1)] (8). These complexes were characterized by NMR and X-ray crystallographic analysis.

The meta–tele-substitution of 2-(boranatophosphino)fluorobenzenechromium complexes took place with various lithiated secondary phosphine–boranes as nucleophiles to give para-substituted bis(boranatophosphino)benzenechromiums. It was revealed that the yield of the tele-substitution product was strongly affected by the strength of a proton acid. Isotope labeling experiments indicated that 1,5-hydrogen migration was involved in this transformation.

The potential of the t-Bu-QuinoxP* ligand (1) as a chiral ligand in asymmetric synthesis was examined. The ligand exhibited good to excellent asymmetric induction in Pd-catalyzed asymmetric allylic substitution of 1,3-diphenyl-2-propenyl acetate (up to 98.7% ee) and in Ru-catalyzed asymmetric hydrogenation of ketones (up to 99.9% ee).

Optically active phosphine ligands possessing stereogenic centers on phosphorus atoms have been synthesized using phosphine-boranes as intermediates. Electron-rich P-chiral phosphine ligands (BisP, MiniPHOS, and DiSquareP) having a bulky alkyl group and a small alkyl group on the phosphorus atom exhibit excellent to almost perfect enantioselectivities in the Rh-catalyzed asymmetric hydrogenation of enamides and related substrates. Air-stable P-chiral phosphine ligands (t-Bu- and 1-Ad-QuinoxP) are also prepared with the phosphine-borane methodology. These ligands have exceedingly high enantioselectivities of up to 99.9% not only in Rh-catalyzed asymmetric hydrogenation but also in Rh- or Pd-catalyzed carbon-carbon bond-forming reactions.

Enantiomerically pure (S,S) -1,2-bis[(o-alkylphenyl) phenylphosphino]ethanes (o-alkylphenyl = o-methylphenyl, o-ethylphenyl, o-isopropylphenyl, 5',6',7',8'-tetrahydro-naphthyl) , (S,S) -1,2-bis (alkyl-methylphosphino) ethanes (alkyl = t-butyl, 1-adamantyl, 1-methylcyclo-hexyl, 1,1-diethylpropyl, cyclopentyl, cyclohexyl) (abbreviated as BisP*) , and (R,R) -1,1-bis (alkylmethylphosphino) methanes (alkyl = isopropyl, t-butyl, cyclohexyl, phenyl) (abbreviated as MiniPHOS) were prepared from phosphorus trichloride via short routes using phosphine-boranes as intermediates. The crystal structures of cationic rhodium complexes, [Rh ((S,S) -1,2-bis ((phenyl) (5',6',7',8'-tetrahydronaphthyl) phosphino) ethane) (cod)]BF4, [Rh ((S,S) -t-Bu-BisP* (nbd))]BF4, and [Rh ((R,R) -t-Bu-MiniPHOS) 2]PF6, clearly indicate the ideal asymmetric environments. These ligands exhibited an excellent to almost perfect level of enantioselectivity in asymmetric hydrogenations of a-dehydroamino acid derivatives and other catalytic asymmetric reactions.

This review deals with new optically active phosphine ligands which appeared in the literature during past eight years. Emphasis is laid on the utility of these ligands in transition metal-catalyzed asymmetric reactions. New methods for the synthesis of chiral phosphine ligands are also described.

(SP)-9-Anthryl(l-menthyloxy)phenylphosphine-borane and (SP)-(1-l-menthyloxy)benzo[b]phosphole-borane were synthesized, and their structures were characterized by X-ray crystallographic analysis. The latter compound was reduced by lithium naphthalenide at −78°C with cleavage of the PO bond, and the subsequent reaction with electrophiles afforded the corresponding tertiary phosphine-boranes possessing good to excellent enantiomeric excesses.

The three-hindered quadrant phosphine ligands (R)-1-tert-butylmethylphosphino-2-(di-tert-butylphosphino)benzene ((R)-3H-BenzP*) and (R)-2-tert-butylmethylphosphino-3-(di-tert-butylphosphino)quinoxaline ((R)-3H-QuinoxP*) exhibited good to excellent enantioselectivities in the rhodium-catalyzed asymmetric hydrogenation of selected dehydroamino acid derivatives, enamides, and ethenephosphonates.

Synthesis and reactions of new phosphine-boranes have been studied. Diastereomerically pure menthyloxyphenylphosphine-boranes were prepared from dichlorophenylphosphine. These secondary phosphine-boranes underwent stereospecific alkylation and arylation reactions. It is noted that the stereochemistry of palladium-catalyzed cross-coupling reactions was largely affected by the solvent and the base used. Thus, the reaction in acetonitrile proceeded with net retention of configuration. In sharp contrast, the reaction in THF in the presence of K2CO3 occurred with inversion of configuration with high degree of stereospecificity. The phosphorus-oxygen bond of the resulting phosphine-boranes was reductively cleaved at -78 "C by lithium naphthalenide or lithium in liquid ammonia in almost quantitative yields with an excellent degree of stereospecificity. On the other hand, the reactions at elevated temperatures provided the products with almost complete racemization. This racemization was proved to occur via pyramidal inversion of the anionic tricoordinate phosphorus species. Based on these results, we developed new methods for the synthesis of bidentate phosphine ligands with homochiral phosphine centers. Optically pure bisphosphinoethanes and bisphosphinobutanes possessing phenyl, t-butyl, cyclohexyl, emethomhenyl, methyl, or 2methoxyethyl group were prepared via phosphine-boranes. Functionalizations of the boranato group of phosphine-boranes have been investigated. Trimethylphosphine-borane reacted with methanesulfonic acid with evolution of hydrogen. The resulting trimethylphosphine-methylsulfonyloxyborane was subjected to nucleophilic substitution reaction on the boron atom with arenthiols or secondary phosphine-boranes. A new phosphine-borane having a P-B-P-B-P-B-P-B bond linkage was synthesized. Novel boron anion species were generated by the reaction of phosphine-monoiodoboranes with lithium 4,4'-dit -butylbiphenylide.

新しい低原子価サマリウム試剤の調製と反応について検討を行った。金属サマリウムと臭素Br2を4:3のモル比で反応させることにより,Sm-SmBr3系反応試剤を調製した,本反応試剤の還元力はヨウ化サマリウム(II)のそれよりも強いことが観察された。たとえば,ヨウ化サマリウム(II)では還元されない芳香族エステルが本反応試剤と室温で容易に反応し,還元的に二量化した生成物を与えた。また,この試剤とシクロプロパン-1,2-ジカルボレ酸ジエチルとの反応では三員環の還元的開裂が起こり,グルタル酸ジエチルが生成した。また,SmBr3-n-BuLi系反応試剤を用いた場合にも,芳香族エステルが還元的に二量化した生成物を与えた。一方,金属サマリウムとヨウ化水銀または臭化水銀を組み合わせた試剤と,シクロプロパン-1,11ジカルボン酸ジメチルの反応は室温で円滑に進行し,ビス[3,3-ビス(メトキシカルボニル)プロピル]水銀が良好な収率で生成した。

New methods for the synthesis of phosphine-boranes including optically active ones have been established. Diphenylphosphine-borane and methyldiphenylphosphine-borane reacted with various electrophiles to give phosphine-borane derivatives having a functional group. Diastereomerically pure secondary phorphine-boranes, (Sp) -and (Rp) -menthyloxyphenylphosphine-boranes, were prepared from dichlorophenylphosphine. These secondary phosphine-boranes underwent stereospecific alkylation and arylation reactions. The phosphorus-oxygen bond of the resulting phosphine-boranes was reductively cleaved by lithium naphthalenide in an almost quantitative yield with virtually net retention of configuration. A new and efficient route to bidentate phosphine ligands with homochiral phosphine center has been established on the basis of these stereochemical studies on the substitution reactions at chiral phosphorus. Functionalizations of the boranato group of phosphine-boranes have been investigated. Trialkylphosphine-boranes reacted with methanesulfonic acid or trifluoromethanesulfonic acid with evolution of hydrogen The resulting sulfonates were subjected to nucleophilic substitution reactions with various nucleophiles including carbon nucleophiles. A new phosphine-borane having a P-B-P-B-P-B-P-B bond linkage was synthesized.

Synthesis and reactions of optically active phosphine-boranes have been investigated. Optically active secondary phosphine-boranes, (Sp)-and (Rp)-menthyloxyphenylphosphine-boranes, and (S)-methylphenylphosphine-borane underwent palla-dium(0)-catalyzed electrophilic arylation with o-, m-, or p-iodoanisole. The stereochemistry of this arylation was largely dependent on the solvent and the base used. The reaction in acetonitrile proceeded with almost complete retention of configuration at the chiral phosphorus, whereas inversion of configuration was observed in ethereal solvents or toluene. The phosphorus-oxygen bond of (Rp)-menthyloxy (methyl) phenylphosphine-borane and (SP)-menthy-loxy(o-methoxyphenyl)phenylphosphine-boranewas reductively cleaved at −78°C by lithium naphtha-lenide or Li/NH3 with virtually net retention of configuration at phosphorus, providing secondary or tertiary phosphine-boranes in excellent yields. New synthetic routes to optically pure C2-symmetric bisphosphine-boranes possessing chirality at phosphorus have been developed on the basis of these stereochemical studies.

The title compound, C9H22BP, and its coupling product, C16H38B2P2, were synthesized and their crystal structures analyzed by X-ray diffraction. The molecular structures clearly explain the stereoselective reaction pathways leading to the products. The average P—B distance and C—P—B angle are 1.929 A and 114°, respectively.

Organocerium reagents are generated by the reaction of organolithiums with anhydrous cerium chloride or cerium io- dide. The reagents are less basic than organolithiums or Gri- gnard reagents, and they react with various carbonyl compounds to give the corresponding addition products in high yields, even though the substrates are susceptible to enolization or metal-halogen exchange with simple organolithiums. The same reagents react with d,g-unsaturated carbonyl compounds to yield lr2-addition products with high regioselectivity. It has also been found that cerium chloride significantly pro- motes the addition reactions of Grignard reagents to carbonyl compounds with remarkable suppression of abnormal reactions. Various tertiary alcohols, which are difficult to prepare by the conventional Grignard reaction, can be synthesized by this method. Several applications of this methodology to practical organic syntheses are described.

Optically active C2-symmetric tetraphosphine 4 was prepared via the phosphine-borane methodology. Its dirhodium complex 5 was structurally characterized and probed as a catalyst in asymmetric hydro...

[reaction: see text] An iridium(I) complex of (S,S)-1,2-bis(tert-butylmethylphosphino)ethane with tetrakis(3,5-bis(trifluoromethyl)phenyl)borate as the counterion catalyzes the hydrogenation of acyclic aromatic N-aryl imines under 1 atm of hydrogen pressure at room temperature to give the corresponding optically active secondary amines with up to 99% ee.

[reaction: see text] (S)-2-(tert-Butylmethylphosphino)phenol and its methyl ether were synthesized from tert-butyldichlorophosphine via optically active phosphine-boranes as the intermediates. The former compound was used as a P/O hybrid ligand in the Cu-catalyzed asymmetric conjugate addition of diethylzinc to acyclic enones to achieve high enantioselectivity of up to 96%.

A new P-chiral phosphine ligand, (R,R)-2,3-bis(tert-butylmethylphosphino)quinoxaline, has been prepared by the reaction of enantiomerically pure tert-butylmethylphosphine-borane with 2,3-dichloroquinoxaline. This ligand, in contrast to most of the previously reported P-chiral ligands, is an air-stable solid and exhibits excellent enantioselectivities in both Rh-catalyzed asymmetric hydrogenations and Rh- or Pd-catalyzed carbon-carbon bond-forming reactions.

Phenol derivatives, which are one of the most important classes of aromatic compounds in organic chemistry, were synthesized by ruthenium-catalyzed ring-closing olefin metathesis (RCM) of 1,4,7-trien-3-ones with versatile substitution patterns. The RCM reaction for producing phenol derivatives was also successful with 1,5,7-trien-3-one as another precursor. Most of the phenols prepared here could not be obtained easily by conventional methods.

Optically active 1,2-bis(alkylmethylphosphino)ethanes and bis(alkylmethylphosphino)methanes are unique diphosphine ligands combining the simple molecular structure and P-stereogenic asymmetric environment. This work shows that these ligands exhibit excellent enantioselectivity in rhodium-catalyzed asymmetric hydrogenation of α,β-unsaturated phosphonic acid derivatives. The enantioselective hydrogenation mechanism elucidated by NMR study is also described.

The reactions of (Rp)-menthyloxymethyl-phenylphosphine-borane with several organolithium reagents are described. Less sterically hindered reagents such as m-anisyllithium and p-anisyllithium react with the phosphine-borane to afford the corresponding substitution products with high stereochemical integrity with inversion of configuration. On the other hand, o-substituted phenyllithiums lead to products possessing very low optical purities.

L'amalgame de cerium est un reactif efficace pour la preparation chimioselective d'alcools homoallyliques a partir d'halogenures allyliques et de composes carbonyles. Ce meme reactif est utilise dans des reactions de type Reformatsky. Les reactifs organiques du Ce(III) generes par reaction d'organolithiens avec CeI 3 ou CeCl 3 sont moins basiques que les organolithiens et les reactifs de Grignard et reagissent avec divers composes carbonyles

Recent developments of organic transformations using lanthanoid elements are described. This review deals also with novel reactions of organolanthanoid complexes which have potential utility in organic synthesis.

The preparation of a new polyphosphate reagent, trimethylsilyl polyphosphate (polyphosphoric acid trimethylsilyl ester) (PPSE), and its use in organic synthesis are described. PPSE is essentially aprotic and soluble in organic solvents and activates oxygen functions under mild conditions for preparative transformations. Some synthetically useful reactions promoted by PPSE are exemplified.

Several thieno[3,2-b]pyridines could be easily synthesized by methallation using LDA directly from 3-(disubstituted amino)-2-cyano-3-methylthioacrylonitriles.

無水塩化セリウム(III)に有機リチウム化合物を反応させ,有機セリウム反応剤を調製した。この反応剤は Grignard 反応剤や有機リチウム反応剤とくらべて塩基性が低く,2-テトラロンや1,3-ジフェニル-2-プロパノンのようなエノール化しやすいケトンとも円滑に反応し,対応する求核付加物を高収率で与えた。またリチウムエノラートに無水塩化セリウムを反応させて得られるセリウムエノラートは,立体的にかさ高いアルデヒドやケトンとも反応し,アルドールを良好な収率で与えた。