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851.
852.
Nicolas Robert 《Tetrahedron》2007,63(18):3702-3706
A concise enantiopure synthesis of six monoterpenic alkaloids of the actinidine series possessing a cyclopenta[c]pyridine skeleton, (+)-deoxyrhexifoline (4), (+)-boschniakinic acid (5), (+)-boschniakine (6), (−)-plantagonine (7), (−)-indicaine (8) and (−)-tecostidine (9) is reported starting with the chiral precursor 3-bromo-5-((4R)-phenyloxazolin-2-yl)pyridine (10). It involves a C-4 regioselective connection of a butene appendice and an intramolecular 5-exo-trig Heck annulation sequence followed by hydrogenation of the exocyclic alkene. Mixture of (3R)- and (3S)-7-((4R)-phenyloxazolin-2-yl)cyclopenta[c]pyridines was separated by HPLC before being transformed into enantiopure natural products (4-9) by modification of the oxazoline group. 相似文献
853.
Diethylzinc-mediated radical addition to CN bonds was investigated in the presence of phenylorganotellurium compounds as radical precursors. As group transfer agents, secondary alkyl phenyl tellurides were shown to be about twice as reactive as the corresponding alkyl iodides towards ethyl radical. Their use was proven to be advantageous regarding both chemoselectivity and yield. The replacement of diethylzinc by dimethylzinc, offers no advantage in these reactions. 相似文献
854.
The synthesis of new β-aminovinyl chloro-difluoromethylated ketones 1 and 2 is presented. In some of them the activation of the C-Cl bond was achieved, under mild conditions, using indium powder. The corresponding difluoro-enolates were trapped with a series of aromatic and heterocyclic aldehydes, to furnish the corresponding difluoromethylene aldol products 3 and 4, in moderate to good yields. The present synthetic methodology provides a convenient approach for the preparation of novel difluoromethylene functionalized enaminone derivatives. 相似文献
855.
Wojciech Dmowski Anna Ja?mu?na Z. Urbańczyk-Lipkowska 《Journal of fluorine chemistry》2007,128(12):1431-1438
Sodium dithionite effectively promotes the addition of dibromodifluoromethane to the exocyclic double bond of β-pinene. The reaction proceeded in a MeCN/H2O system to give almost quantitatively an adduct, 1-(2-bromo-2,2-difluoroethyl)-4-(2-bromoisopropyl)-cyclohexene, as the sole product. On treatment of the adduct with 2,2,6,6-tetramethylpiperidine elimination of HBr only from the (CH3)2CHBr group occurred to give a mixture of regioisomeric dienes, while treatment with 50% KOH under phase transfer catalysis conditions or with K2CO3 in DMF resulted in total dehydrobromination to give trienes possessing an exocyclic CHCF2 group. Surprisingly, the main course of the reactions of the adduct with DBU (1,8-diazabicyclo[5.4.0]undece-7-ene) and also with t-BuOK in THF was elimination of HBr only from the CH2CF2Br group to afford 1-(2,2-difluorovinyl)-4-(2-bromoisopropyl)cyclohexene as the main product. Catalytic hydrogenation of the adduct followed by treatment with DBU afforded a conjugated diene, 1-(2,2-difluorovinyl)-4-isopropylcyclohexene. Compounds bearing the CHCF2 group are new 1,1-difluorodienes which readily reacted with 4-phenyl-3H-1,2,4-triazoline-3,5-dione to give cycloadducts, derivatives of triazolo[1,2-α]cinnoline. 相似文献
856.
Angelino Doppiu 《Journal of organometallic chemistry》2007,692(21):4495-4505
The optically active indenyl-linked phosphane ligands (S)-[2-(3H-inden-1-yl)-1-phenylethyl]diphenylphosphane (L1) and (S)-[2-(4,7-dimethyl-3H-inden-1-yl)-1-phenyl-ethyl]diphenylphosphane (L2) were synthesized in three steps from (R)-1-phenylethane-1,2-diol in excellent yields. Their lithium salts reacted with [Rh(μ-Cl)(η2-CH2CH2)2]2 at −78 °C in THF affording the planar chiral complexes (S,Rpl + Spl)-[Rh(η5-indenyl-CH2CH(Ph)PPh2-kP)(η2-CH2CH2)] and (S,Rpl + Spl)-[Rh(η5-4,7-dimethylindenyl-CH2CH(Ph)PPh2-kP)(η2-CH2CH2)] as 61:39 and 15:85 mixtures of diastereomers. The complexes were isolated in optically pure form by column chromatography. The stereochemical configuration of one of the diastereomers was determined by X-ray crystallography. The complexation of L2 was studied in different solvents and with several Rh precursors and diastereomeric excesses up to 76% were achieved. The ability of the chiral ligands to control the stereochemistry at the metal center was tested by oxidative addition of methyl iodide. Diastereomeric excesses greater than 98% were observed. 相似文献
857.
Dmitrii P. Krut’ko Roman S. Kirsanov Maxim V. Borzov Andrei V. Churakov 《Journal of organometallic chemistry》2007,692(7):1465-1471
Half-sandwich [η5:η1-κN-C5Me4CH2-(2-C5H4N)]MCl3 (M = Ti (4), Zr (5)) and sandwich [η5-C5Me4CH2-(2-C5H4N)][η5-C5Me5]ZrCl2 (6) ring-peralkylated complexes have been prepared and characterized. Evidence of the intramolecular coordination of the side-chain pyridyl group both in 4 and 5 in solutions is provided by NMR spectroscopy data. Crystal structure of an adduct 5-py with one molecule of pyridine has been established by X-ray diffraction analysis. 相似文献
858.
Stefan Dilsky 《Journal of organometallic chemistry》2007,692(14):2887-2896
Starting from [M(CO)6], seven-coordinated complexes of tungsten and molybdenum containing the facially coordinating ligands HC(pz)3 (1) and MeC(CH2PPh2)3 (2) were obtained in a two-step reaction sequence. The complexes have a 4:3 piano stool geometry with almost perfect CS symmetry in the crystal. In solution, they show the typical fluxional behavior for seven-coordinated complexes even at low temperature. Complete oxidative decarbonylation occurs when [HC(pz)3Mo(CO)3] (4) or [MeC(CH2PPh2)3Mo(CO)3] (6) are treated with an excess of I2 or Br2. 相似文献
859.
Akella Sivaramakrishna 《Journal of organometallic chemistry》2007,692(23):5125-5132
The synthesis, characterization and chemistry of novel η3-allyl metal complexes (M = Ir, Rh) are described. The structures of compounds (C5Me4H)Ir(PPh3)Cl2 (1), (C5Me4H)Ir(PPh3)(η3-1-methylallyl)Br (3a), (C5Me4H)Ir(η4-1,3,5-hexatriene) (8), and (C5Me5)Rh(η3-1-ethylallyl)Br (5d) have been determined by X-ray crystallography. Structural comparisons among these complexes are discussed. It is found that the neutral metal allylic complex [Cp∗IrCl(η3-methylallyl)] (5) ionizes in polar solvents to give [Cp∗Ir(η3-methylallyl)]+Cl− (6) and reaches equilibrium (5 ? 6) at room temperature. Addition of tertiary phosphine ligands to neutral complexes such as [Cp∗Ir(η3-methylallyl)Cl], results in the formation of stable ionic phosphine adducts. Factors such as solvent, length of carbon chain, temperature and light are discussed with respect to the formation, stability and structure of the allyl complexes. 相似文献
860.
Compound CpMoI2(iPr2dad) (iPr2dad = iPrNCHCHNiPr), obtained by halide exchange from CpMoCl2(iPr2dad) and NaI, has been isolated and characterized by EPR spectroscopy, cyclic voltammetry, and X-ray crystallography. Its action as a catalyst in atom transfer radical polymerization (ATRP) and as a spin trap in organometallic radical polymerization (OMRP) of styrene and methyl acrylate (MA) monomers has been investigated and compared with that of the dichloro analogue. Compound CpMoCl2(iPr2dad) catalyzes the ATRP of styrene and MA with low efficiency factors f (as low as 0.37 for MA and ethyl 2-chloropropionate as initiator), while it irreversibly traps the corresponding growing radical chains under OMRP conditions. On the other hand, compound CpMoI2(iPr2dad) has a greater ATRP catalytic activity than the dichloro analogue and yields f = 1 for MA and ethyl 2-iodopropionate as initiator. Under OMRP conditions, it does not irreversibly trap the growing radical chains. This comparison serves to illustrate the general principle that low initiator efficiency factors, sometimes observed in ATRP, may result from the interplay of the ATRP and OMRP mechanisms, when the latter ones involves an irreversible radical trapping process. 相似文献