Asymmetric formal synthesis of (−)-pancracine via catalytic enantioselective C-H amination process

The reaction of silyl enol ethers derived from cyclohexanone with [(4-nitrophenylsulfonyl)imino]phenyliodinane (pNsNIPh) catalyzed by dirhodium(II) tetrakis[N-tetrachlorophthaloyl-(S)-tert-leucinate], Rh₂(S-TCPTTL)₄, provides, after desilylation, N-pNs-protected (S)-β-aminocyclohexanone in up to 72% ee. This represents the first example of the insertion of nitrene species into an allylic C-H bond of silyl enol ethers. Using this process, a new catalytic asymmetric route to an advanced intermediate in Overman's synthesis of the montanine-type Amaryllidaceae alkaloid (−)-pancracine has been developed. The key steps involve (a) a one-pot Rh₂(R-TCPTTL)₄-catalyzed sequential 1,4-hydrosilylation/enantioselective C-H amination of 2-cyclohexen-1-one, (b) N-alkylation and subsequent intramolecular Mukaiyama aldol reaction/dehydration, and (c) a regio- and stereocontrolled reductive deoxygenation of bicyclic enone 27 with migration of the double bond to create the C1/C11a double bond and the stereogenic center at C11 of 3-arylhexahydroindole 31.     

Pd(II)-catalyzed oxidative cyclization reaction for the preparation of 2-substituted 1,2,3,4-tetrahydroquinolines with halide functionality

The first Pd(II)-catalyzed oxidative cyclization reaction was developed for preparation of 2-substituted 1,2,3,4-tetrahydroquinolines from olefinic tosylamides. Under the optimized conditions, up to 86% yield was obtained. This reaction provides direct and easy access to 2-substituted 1,2,3,4-tetrahydroquinolines with halide functionality.     

Catalytic hydrogenation by recyclable supported Pd(II)-amino acid complex

L-phenyl alanine was anchored to P(S-DVB) resin and its complex with PdCl₂ was prepared. The newly synthesized catalyst was found to be a versatile and recyclable catalyst for the hydrogenation of 1-octene and acetophenone. This chiral catalyst induced moderate enantioselectivity during the asymmetric reduction of acetophenone. This revised version was published online in June 2006 with corrections to the Cover Date.     

Rapid Suzuki‐Miyaura cross‐coupling reaction catalyzed by zirconium carboxyphosphonate supported mixed valent Pd(0)/Pd(II) catalyst

Mixed valent Pd(0)/Pd(II) nano‐sized aggregates supported onto a chemically robust layered zirconium carboxyphosphonate framework is prepared and its catalytic activity in Suzuki‐Miyaura cross coupling reaction is explored. The exceptionally high catalytic efficacy of the heterogeneous catalyst in Suzuki‐Miyaura cross coupling reaction is signified by remarkably short reaction time 2 minutes and high turnover frequency of 1.3 x 10⁴ hr^?1. The catalyst can be recycled several times without significant loss of catalytic efficacy, while spectroscopic, structural and microscopic investigations suggest the integrity of the catalyst even after fifth catalytic cycle. The unique ability of the zirconium carboxyphosphonate framework to interact strongly with palladium in dual Pd(0)/Pd(II) oxidation states has been attributed to this remarkable augmentation of catalytic efficacy.     

The novel approach to indole alkaloids by using Pd(II)-catalyzed cyclization

The synthesis of indole skeleton by using Pd(II)-catalyzed cyclization of the urethane has been achieved. The urethanes with allylic alcohol were converted into vinyl indolines in good yield. The vinyl indoline was transformed into some intermediates of indole alkaloids.     

Pd(0) or Pd(II)-catalyzed ring-opening reactions of benzylidene- and alkylidenecyclopropyl ketones and aldehydes

Pd(0) catalyzed reactions of methylenecyclopropyl carbonyl compounds afforded a convenient method for the synthesis of conjugate (E,E)-1,3-diene derivatives 2 in good to excellent yields. Moreover, we also found that Pd(II)-catalyzed reactions of methylenecyclopropyl carbonyl compounds with water gave 1,5-diketones in good to high yields via a carbene-palladium intermediate. The plausible reaction mechanisms have also been provided on the basis of control and ¹⁸O-labeling experiments.     

Construction of indoloquinolinones via Pd(II)-catalyzed tandem CC/CN bond formation: application to the total synthesis of isocryptolepine

Construction of indoloquinolinone skeleton via Pd-catalyzed tandem CC/CN bond formation has been achieved in moderate to good yields. The method was applied toward the total synthesis of the bioactive natural product isocryptolepine in good overall yields.     

Spectral and photophysical properties of mono and dinuclear Pt(II) and Pd(II) complexes: An unusual emission behaviour

Eight mononuclear complexes of the formula [M(N-N)(DHB)] and two binuclear complexes of the formula [M₂(BPY)₂(THB)] where M = Pd(II) or Pt(II), N-N = 2,2′-bipyridine (BPY), 2,2′-biquinoline (BIQ), 4,7-diphenyl-1,10-phenanthroline (DPP), 1,10-phenanthroline (PHEN); DHB = dianion of 3,4-dihydroxybenzaldehyde and THB = tetraanion of 3,3′,4,4′-tetrahydroxy benzaldazine were prepared and their electrochemical, spectral and photophysical properties were examined. These complexes were characterized by chemical analysis, IR and proton NMR spectroscopy. A detailed study on the absorption spectroscopy of these complexes was made. These complexes were found to show a low-energy solvatochromic ligand-to-ligand charge-transfer (LLCT) band. The electronic energies of these bands have been analyzed and compared with electrochemical data. Emission behaviour of the complexes of the series, [Pt(N-N)(DHB)], [Pt(N-N)(DHBA)] where DHBA is the dianion of 3,4-dihydroxybenzoic acid and [Pt₂(BPY)₂(THB)] was also investigated. These platinum complexes were found to emit from a low-energy state at low temperature and a high-energy state at room temperature. Photophysics of these complexes is also discussed.     

Cu(II)-catalyzed enantioselective aldol condensation between malonic acid hemithioesters and aldehydes

A mild, decarboxylative, aldol-type addition of malonic acid hemithioesters to aldehydes has been shown to occur with up to 39% enantioselectivity when the reaction was carried out in the presence of catalytic amounts of a Cu(II) salt, an enantiopure, tartaric acid-derived bis-benzimidazole and an achiral base.     

Palladium(II)-catalyzed aerobic intramolecular allylic CH activation for the synthesis of indolines

A method for the preparation of indolines via palladium-catalyzed aerobic intramolecular allylic CH activation was developed. Oxygen was successfully used as oxidant with catalytic amount of 1,4-benzoquinone. 16 examples were reported, the majority of substrates gave moderate to good yields.     

Cobalt(II)-catalyzed direct acetylation of alcohols with acetic acid

Cobalt(II) chloride hexahydrate (CoCl₂·6H₂O) efficiently catalyzes the acetylation of alcohols with AcOH in high yields. This protocol is also effective with other carboxylic acids, trifluoroacetic acid, propanoic acid, phenylacetic acid and benzoic acid, affording the corresponding acylated products in moderate to good yields. Removal of water is not necessary in these reactions. The catalyst can be filtered and recycled without loss of activity.     

Kinetics and mechanism of electroreduction of Pd(II) complexes

The kinetics and mechanism of processes of reduction of Pd(II) complexes with a number of inorganic (NH₃ , Cl^– , etc.) and organic (ethylenediamine, glycine, -alanine, etc.) ligands on a dropping-mercury electrode and a Pd electrode in solutions with various concentrations of ligands, hydrogen ions, and supporting electrolytes are reviewed. The nature of electrochemical and chemical steps of processes of reduction of various complexes of Pd(II) is discussed.Translated from Elektrokhimiya, Vol. 40, No. 12, 2004, pp. 1494–1502.Original Russian Text Copyright © 2004 by Kravtsov.     

SYNTHESIS AND STRUCTURE OF Pd(II) COMPLEXES OF 1,2,3-TRIPHENYLGUANIDINE

Abstract

The formation of two complexes by reaction of [PdCl₄]^2- with 1,2,3-triphenylguanidine (PhNH)₂C=NPh under different metal/ligand ratios has been observed and the structure of the complex [(1,2,3-triphenylguanidine)₂PdCl₂] has been determined by X-ray diffraction methods. The ligands are coordinated as neutral monodentate molecules to the metal centre through their imine nitrogen atoms. The second Pd(II) complex is [Pd(1,2,3-triphenylguanidine)₄]²⁺ and was isolated by precipitation with ClO^? ₄.     

Functionalized cyclopentanes via Sc(III)-catalyzed intramolecular enolate alkylation

We report herein the intramolecular α-tert-alkylation of unsaturated β-ketoesters which gives rise to highly functionalized cyclopentanes. This transformation is characterized by its operational simplicity, mild reaction conditions and the use of scandium (III) triflate as a Lewis acid catalyst. Of interest, cyclopentanes bearing heterocycles, sites for post reaction functionalization and spirocyclic architectures are accessible with this strategy.     

Cu(I)/Cu(II)-catalyzed allylic amination of alkenes

Allylic hydrocarbons are selectively converted to the corresponding allyl amines in good to excellent yield by reaction with aryl hydroxylamines catalyzed by a 1:1 mixture of CuCl and CuCl₂ (10 mol %). Under these conditions unsymmetrical olefins react highly regioselectively with N-functionalization at the less substituted vinylic carbon. Trapping experiments indicate that a free nitrosoarene is not an intermediate in these reactions.     

Co(III)/Zn(II)-catalyzed dearomatization of indoles and coupling with carbenes from ene-yne ketones via intramolecular cyclopropanation

A straightforward and efficient protocol for dearomatizing indoles is described. The reaction, catalyzed by an inexpensive Co(III)/Zn(II) catalyst, starts from easily accessible N-pyrimidinyl indoles and ene-yne ketones. Mild reaction conditions, high diastereoselectivity, a broad substrate scope, effective functional group tolerance, and reasonable to remarkable yields were observed.     

Six-membered ring chelate complexes of Pd(II) and Pt(II) derived from di-(2-pyridyl)pyrimidin-2-ylsulfanylmethane

Cis-[MLCl₂] complexes of di-(2-pyridyl)pyrimidin-2-ylsulfanylmethane ligand (L), where M = Pd (1), and M = Pt (2) have been synthesized. Reaction of 1 with L in presence of Na[BF₄] and hot acetonitrile produced the complex [PdL₂](BF₄)₂ (3). Complexes 1-3 and ligand L have been characterized by elemental analyses, IR and NMR spectroscopy. Crystal structures of 1, 3 and L were determined by single crystal X-ray diffraction analyses, showing nonplanar structures with the pyridinic rings twisted around the bridging carbon and the ipso carbon bonds. 1 and 3 displayed a bidentate coordination of L to the palladium atom with the formation of six-membered chelate rings, where the local geometry at palladium atom was distorted square planar. In 3 the palladium atom was coordinated to two dipyridyl ligands through two of the pyridinic nitrogen atoms to form a cationic complex stabilized by two tetrafluoroborate counter-ions.     

Pd(II)-catalyzed coupling-cyclization reaction of o-ethylnylphenylphosphonamides monoesters with allyl halide

4-Allyl-phosphaisoquinolin-1-ones were synthesized by palladium-catalyzed coupling-cyclization of o-ethynylphenylphosphonamide monoethyl esters with allyl halides with high regioselectivity and good yields. The synthesized 4-allyl-phosphaisoquinolin-1-ones show bioactivity as inhibitor of MCH-1R.