Asymmetric synthesis of secondary benzylic alcohols via arene chromium tricarbonyl complexes

(Aryl aldehyde)- and (aryl ketone)-chromium tricarbonyl complexes ortho-substituted with the chiral auxiliary O-methyl-N-(α-methylbenzyl)hydroxylamine undergo diastereoselective addition of Grignard reagents and Super-Hydride^®, respectively, to give the corresponding secondary alcohols in high diastereoisomeric purity. These compounds may be easily decomplexed and deprotected to give the corresponding enantiopure amino alcohols.     

Stereocontrolled [3 + 2] annulations with arene chromium tricarbonyl complexes: construction of spirocyclic compounds related to fredericamycin A

[reaction: see text] An efficient method has been developed for the stereocontrolled construction of polycyclic and spirocyclic compounds, including the spirocyclic core of the antitumor agent fredericamycin A. The strategy involves a one-pot aldol addition/Brook rearrangement/cyclization sequence beginning from arene chromium tricarbonyl complexes and can formally be described as a [3 + 2] annulation.     

Heterogeneous and homogeneous hydrogenation of styrene and stilbene chromium tricarbonyl complexes

Heterogeneous hydrogenation of the styrene and stilbene chromium tricarbonyl complexes by molecular hydrogen on skeletal nickel and palladium on carbon as catalysts was studied. As compared to styrene and stilbene, their arene chromium tricarbonyl analogs are hydrogenated considerably more slowly, which is related, most likely, to strong adsorption of the π-complexes on the catalyst surface. For the homogeneous hydrogenation of these complexes using a H₂PtCl₆-SnCl₂-LiBr system, styrene and η⁶-styrene chromium tricarbonyl are reduced with a high rate, whereas stilbene and its chromium tricarbonyl complex are hydrogenated very slowly. A possibility of reduction of the unsaturated arene chromium tricarbonyl complexes by sodium borohydride in the presence of cobalt(II) chloride as a catalyst was shown. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 44–47, January, 2007.     

Solvent and structural effects on ultrafast chelation dynamics of arene chromium tricarbonyl sulfide derivatives

The chelation dynamics of three new [Cr{eta6-C6H5C(O)R}(CO)3] complexes, 1 [R = CH2(SCH3)], 2 [R = CH(SCH3)2], and 3 [R = C(SCH3)3], has been investigated on the picosecond to millisecond time scales by UV pump/IR probe transient absorption spectroscopy following photodissociation of CO in room temperature n-heptane, tetrahydrofuran (THF), and acetonitrile. In n-heptane, UV irradiation of 1, 2, or 3 dissociates CO to initially yield a Cr-S chelate (in which the pendant sulfide moiety is coordinated to the metal center) and a transient Cr-heptane solvate in approximately 1:2, 1:2, and 2:1 ratios, respectively. The Cr-heptane solvate is unstable and converts to the Cr-S chelate within 30 ns in each case. Irradiation of 2 or 3 in THF yields both the Cr-S chelate and Cr-THF solvate in approximately 1:3 and 1:1 ratios, respectively. The Cr-THF solvate converts to the Cr-S chelate on the second or longer time scale. All three complexes appear to yield the Cr-NCCH3 solvate exclusively within 50 ps following irradiation in acetonitrile. The solvent effect on chelation is in striking contrast to that previously reported for the analogous RCpMn(CO)3 derivatives, 4-6. In acetonitrile, only chelation is observed for the Mn series and only solvent coordination is observed for the Cr series, but in heptane both chelation and solvent coordination are observed in both series.     

Vicinal stereocontrol during nucleophilic addition to arene chromium tricarbonyl complexes: formal synthesis of (+/-)-erythro Juvabione

[reaction: see text] Vicinal stereocontrol during nucleophilic addition of tert-butyl lithiopropionate to eta(6)-anisole chromium tricarbonyl complexes with differing para substituents has been studied. Excellent vicinal double stereoinduction (>99:1) was observed when the para substituent was Si(CH(3))(3), and this has been applied to a stereoselective formal synthesis of (+/-)-erythro Juvabione. Asymmetric synthesis by chiral auxiliary directed nucleophilic addition is also discussed.     

Gold(I)-catalyzed asymmetric synthesis of planar chiral arene chromium complexes

Gold(I)-catalyzed asymmetric cyclization of 1,3-dihydroxymethyl-2-alkynylbenzene chromium complexes gave planar chiral isochromene chromium complexes with high enantioselectivity. Enantiomeric excess of the cyclization products was largely affected by a combination of axially chiral diphosphine(AuCl)(2) precatalysts and silver salts. A system of segphos(AuCl)(2) with AgBF(4) resulted in the formation of the corresponding antipode.     

Synthesis and characterization of organometallic conjugated polymers containing tricarbonyl(arene)chromium unit and platinum

Novel organometallic conjugated polymer containing (η⁶-arene)Cr(CO)₃ and platinum in the main chain was synthesized by dehydrohalogenation coupling reaction of (η⁶-1,4-diethynylbenzene)tricarbonylchromium with trans-(PBu₃)₂PtCl₂. The polymer was soluble in common organic solvents and has the number-average molecular weight of 31,000 by GPC analysis. The polymer exhibited an absorption peak derived from π-π^∗ interaction at 358 nm in the UV-Vis spectrum, which showed a red shift of approximately 90 nm compared to that of the model compound. The photochemical ligand exchange reaction of the polymer was also investigated.     

Insect pheromones and their analogs. LX. Stereocontrolled synthesis of sex pheromones ofDrosophila mulleri andMayetiola destructor

Syntheses are developed for 2S-tridecyl- and 2S-tridec-10E-enylacetates, sex pheromones of the fruit flyDrosophila mulleri and the Hessian flyMayetiola destructor, respectively, that are based on ethyl-3S-hydroxybutanoate, a product from enzymatic reduction of ethyl acetoacetate by the soil yeast strain 80-1.Work performed under the auspices of the Federal program Integratsiya of the RF (Contract No. A 0005).Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 167–169, March–April, 2000.     

Synthesis and properties of PPE-type conjugated polymers containing tricarbonyl(arene)chromium unit in the main chain

Novel π-conjugated polymers containing (η6-arene)Cr(CO)₃ in the main chain based on poly(p-phenylene-ethynylene) were prepared by the Sonogashira coupling reaction of η6-(1,4-diethynylbenzene)tricarbonylchromium with 1,4-diiodo-2,5-dialkoxybenzenes. The polymers were soluble in common organic solvents and characterized by NMR and FT-IR spectra. The polymers exhibited an absorption maximum at around 390 nm, which showed a red shift of approximately 30 nm compared to that of the model compound. Cyclic voltammogram showed a single reversible oxidation peak derived from the (η6-arene)Cr(CO)₃ unit.     

A new strategy for the synthesis of aryl- and heteroaryl-substituted exocyclic olefins from allyl alcohols using PBr3

Treatment of aryl and heteroaryl substituted allyl alcohols 7-14 with phosphorus tribromide at 0 °C furnished a new series of substituted exocyclic olefins 15-22 in good yields. The +I inductive effect of substituents on the aryl group is described.     

Stereocontrolled total synthesis of fucoxanthin and its polyene chain-modified derivative

Fucoxanthin exhibits high energy transfer efficiencies to Chlorophyll a (Chl a) in photosynthesis in the sea. In order to reveal how each characteristic functional group, such as the length of the polyene chain, allene, and conjugated carbonyl groups, of this marine natural product are responsible for its remarkably efficient ability, the total synthesis of fucoxanthin by controlling the stereochemistry was achieved. The method established for fucoxanthin synthesis was successfully applied to the synthesis of the C42 longer chain analogue.     

Efficient synthesis of functionalized olefins by Wittig reaction using Amberlite resin as a mild base

A convenient procedure for the synthesis of olefins by the reaction of stabilized, semistabilized, and nonstabilized phosphorous ylides with various aldehydes or ketone using Amberlite resin as a mild base is described. Our developed method offers facile and racemization-free synthesis of α,β-unsaturated amino esters and chiral allylic amine. The developed methodology offers mild reaction conditions, high efficiency, and facile isolation of the final products, a practical alternative to known procedures.     

Intramolecular Vinyl Radical Cyclization Reactions of cyclohexadienes derived from sequential additions to (arene)(tricarbonyl)chromium complexes. Preliminary communication

Cyclohexa-1,3-dienes 7–10 with a 1,5,6-substitution pattern were prepared in a one-pot reaction sequence by sequential addition of MeLi and propargyl bromides to the tricarbonylchromium complex 1a . These products were subjected to radical cyclization procedures. Vinyl radical generation by Bu₃Sn addition to the propargyl group in 7–10 was followed by regio- and diastereoselective intramolecular ring closure. Two different 5-exo-trig cyclizations are possible via different vinyl radical intermediates and cyclization to one or the other of the termini of the cyclohexadiene moiety. Internal alkynes reacted to yield exclusively the cis-fused hexahydroindene products 12–14 , whereas the terminal alkyne yielded bicyclo[3.2.1]octenes 11 as sole products.     

Asymmetric hydrogenation of imines and olefins using phosphine-oxazoline iridium complexes as catalysts

Herein we describe the synthesis of a new class of chiral phosphine-oxazolines and their application as ligands in iridium-catalyzed hydrogenations. Mechanistic aspects of olefin hydrogenation with this class of iridium catalysts are discussed and a selectivity model to help rationalize the results obtained is also presented.     

水热法Fe-Mn催化剂制备及其合成气制低碳烯烃催化活性

以水热合成法制备了K原位改性的Fe-Mn催化剂,考察了其CO加氢合成低碳烯烃催化活性。采用SEM、TEM、XRD、H₂-TPR和FT-IR等手段对催化剂进行了表征。结果表明,制备的催化剂前驱体呈50~70 nm的球形颗粒,表面富含羰基和羟基,物相组成以Fe₃O₄为主,用于反应后有Fe₅C₂和MnCO₃相生成。与共沉淀法制备催化剂相比,在设定的反应条件下,不同K含量改性的催化剂均具有较高的活性,以原料配比Fe:Mn:C₆:K=3:1:5:0.10的催化剂性能最佳,CO转化率达95.02%,总低碳烯烃收率为62.86 g/m³(H₂+CO),CH₄和CO₂选择性分别为13.88%和13.98%。     

Studies on spiroborate complexes—I. A new synthesis of bis-catechol spiroborate and its analogs using 2-amino-4-methylpyridine borane

A new synthesis of bis-catechol spiroborate and its analogs are described. Not only five-but also six- and seven-membered spiroborates are obtained. The reaction mechanisms are also discussed.