Palladium-Catalyzed Sequential Twofold Nucleophilic Substitution on 3‑Bromopenta-2,4-dienyl Phosphate: Preparation of <i>C</i>₁- and <i>C</i>₂‑Symmetric Doubly Functionalized Allenes

Readily available 3-bromopenta-2,4-dienyl esters (1x, acetate; 1y, benzoate; 1z, diethyl phosphate) were applied to the palladium-catalyzed reaction with various soft nucleophiles. The reaction proceeded through the twofold nucleophilic substitution via formal SN2′- and SN2-processes, giving the various doubly functionalized allenes 2 in good yields. In the reactions of carboxylates 1x and 1y, the first substitution took place at the C–Br bond to form (allenyl)­methyl ester intermediates 3. Because the second substitution on 3 proceeded faster than the first substitution on 1x or 1y, 3 was not isolable, and C2-symmetric allenes 2 were obtained even in the presence of remaining 1x and 1y. On the other hand, the phosphate moiety was more reactive than the C–Br moiety in 1z. The initial products from 1z were 5-Nu-3-bromopenta-1,3-dienes 4, which were less reactive than 1z. Monosubstitution products 4 were isolable, and the stepwise introduction of two different Nu groups in C1-symmetric allenes 2 was realized starting with 1z under the controlled reaction conditions. By the use of a chiral palladium catalyst, axially chiral doubly functionalized allenes were obtained up to 95% ee

Application of Polysaccharide-Based Chiral High-Performance Liquid Chromatography Columns for the Separation of Regio‑, <i>E</i>/<i>Z</i>‑, and Enantio–Isomeric Mixtures of Allylic Compounds

Daicel Chiralpak IA, IB, and IC, which are the polysaccharide-based chiral stationary phase (CSP) columns for high-performance liquid chromatography (HPLC), were applied in the separation of the non-enantiomeric isomeric mixtures obtained by the various allylation reactions and were highly effective in separating the regio- and (E)/(Z)-isomers in the allylation products. Due to the close structural similarity of the isomeric allylic compounds in the reaction mixtures, separations of the isomers are laborious and could not be accomplished by the conventional methods such as silica gel column chromatography, silica gel HPLC, preparative GPC, distillation, and so forth. This study has shown potential advantages of using the polysaccharide-based CSP columns in the separation of not only enantiomeric but also non-enantiomeric isomeric mixtures

A New Type of Catalytic Tandem 1,4-Addition−Aldol Reaction Which Proceeds through an (Oxa-π-allyl)rhodium Intermediate

The reaction of 9-aryl-9-borabicyclo[3.3.1]nonanes (B-Ar-9BBN) with α,β-unsaturated ketones and aldehydes in the presence of 3 mol % [Rh(OMe)(cod)]2 in toluene at 20 °C for 2 h gave high yields of the tandem 1,4-addition−aldol reaction products with high syn selectivity. The reaction proceeds through the catalytic cycle consisting of 1,4-addition of an organorhodium species to an α,β-unsaturated ketone and the aldol addition of the resulting (oxa-π-allyl)rhodium intermediate to an aldehyde

Induction of Atropisomeric Chirality on Heavily Substituted Phosphametallocenes

The solution behavior of the diphospha- and the monophosphametallocenes with (−)-menthyl substituents was investigated by variable-temperature NMR measurements in toluene-d8. Because of the bulky and chiral (−)-menthyl substituents which restrict the rotation of the η5-phospholyl/η5-cyclopentadienyl ligands with respect to each other, the tetra[(−)-menthyl]phosphametallocenes were observed as mixtures of two slowly interconverting diastereomers

2,2‘-Bis(diphenylphosphino)-1,1‘-biphenyl: New Entry of Bidentate Triarylphosphine Ligand to Transition Metal Catalysts

The bidentate triaryl phosphine 2,2‘-bis(diphenylphosphino)-1,1‘-biphenyl (dpbp) was examined as a supporting ligand in several transition metal catalysts. The dpbp complexes showed superior catalytic activity to the corresponding complexes of other bisphosphines in Pd-catalyzed Grignard cross-coupling and Rh-catalyzed Michael addition of boronic acid. In the Pd-catalyzed Grignard cross-coupling of sec-BuMgCl, the Pd-dpbp catalyst showed nearly perfect secondary selectivity in the product. This selectivity is much higher than that of Pd catalysts with other standard bisphosphines and is comparable only with that of the corresponding Pd-dppf catalyst. Dpbp was also applied to Rh-catalyzed conjugate addition of boronic acids to enones, and the Rh(acac)(C2H4)2/dpbp catalyst exhibited excellent catalytic activity, which is far better than the corresponding catalyst with dppb. The structure of the dpbp complex PdCl2(dpbp) was studied by X-ray single-crystal structure determination, which clarified the bite angle of dpbp in the complex being 92.24°

A New Route to Methyl (<i>R,E</i>)-(−)-Tetradeca-2,4,5-trienoate (Pheromone of <i>Acanthoscelides</i> <i>obtectus</i>) Utilizing a Palladium-Catalyzed Asymmetric Allene Formation Reaction

A formal total synthesis of the sex attractant of male dried bean beetle, methyl (R,E)-(−)-tetradeca-2,4,5-trienoate, was achieved by a new efficient route utilizing the Pd-catalyzed asymmetric allene synthesis reaction. It was found that the atropisomeric biaryl bisphosphine (R)-segphos showed better enantioselectivity than (R)-binap in the Pd-catalyzed reaction for preparing alkyl-substituted axially chiral allenes

Synthesis and Characterization of a Novel Chiral Phosphole and Its Derivatives

A novel chiral and enantiomerically pure phosphole with two (−)-menthyl groups at the 2- and 5-positions of the phosphole ring is prepared in two steps, starting from (−)-menthylacetylene, in 67% overall yield. This is the first example of a chiral phosphole in which chiral substituents attach directly to the carbon atoms of the phosphole ring. The phosphole was characterized by X-ray crystallography, and its solid-state structure has no symmetry, with an envelope-like bent structure for the five-membered ring. The phosphole was readily oxidized into the corresponding phosphole oxide, and reaction with MCl2(cod) (M = Pt, Pd) led to two chiral phosphole−transition-metal complexes, trans-MCl2(phosphole)2, quantitatively. Treatment of the phosphole with metallic lithium in THF cleaved the exocyclic P−Ph bond to give a chiral lithium phospholide with retention of the two (−)-menthyl substituents. The lithium phospholide was converted into a chiral diphosphole in 62% yield by reaction with BrCH2CH2Br and into a chiral monophosphaferrocene in 85% yield by reaction with [(η6-mesitylene)FeCp]PF6. A reaction of the phosphole with Mn2(CO)10 in refluxing xylene gave a chiral phosphacymantrene in 84% yield

Metathesis Route to Bridged Metallocenes

A variety of bridged metallocenes of Fe(II), Ru(II), Zr(IV), or Hf(IV) were prepared in good yield by the interannular ring-closing metathesis reaction of 1,1‘-diallylmetallocenes using the Ru-carbene catalyst, and the present method was extended to diastereoselective reaction to give dl- or meso-bridged metallocenes with excellent stereoselectivity

Synthesis of 1,1‘-Diphospha[4]ferrocenophanes by Molybdenum-Catalyzed Ring-Closing Metathesis

A variety of 1,1‘-diphospha[4]ferrocenophanes were prepared in good to moderate yield with the interannular ring-closing metathesis reaction of diallyl-1,1‘-diphosphaferrocenes using the Schrock's molybdenum-carbene catalyst. The Grubbs' ruthenium metathesis catalyst was found inactive for these Lewis basic phosphorus-containing substrates

Rhodium-Catalyzed Asymmetric Conjugate Addition of Organoboronic Acids to Nitroalkenes

Rhodium-Catalyzed Asymmetric Conjugate Addition of Organoboronic Acids to Nitroalkene