New ferrocene-containing structures: Poly(silyl ester)s

Two new polymeric structures containing ferrocene units along the chains, namely poly(silyl ester)s, have been synthesized and characterized: a geminal poly(silyl ester) (g-PSE) and one having a disiloxane spacer between the silyl ester groups (s-PSE). The condensation polymerization of AA/BB monomer systems in solution was used in both cases as preparation method involving a silicon-containing diol, (diphenylsilane diol or 1,3-bis(hydroxy)-tetramethyldisiloxane), and 1,1′-di(chlorocarbonyl)ferrocene. The polymers were investigated by differential pulse voltammetry in order to evaluate the redox behavior. Due to the presence of the silyl ester groups in the chain, these polymers are hydrolytically degradable.     

一种新型的芳基重排反应（Ⅱ）──苯并环己酮中β－芳基的重排

报道了３－芳基四氢合萘－１－酮的烯醇硅醚在氧化碘苯－三氟化硼的协同作用下３－位芳基迁移到２－位，生成２－芳基－３－氟四氢合萘－１－酮的反应。当芳基是Ｐｈ－ｐ－Ｃｌ－Ｐｈ、ｐ－Ｍｅ－Ｐｈ和ｐ－ＭｅＯ－Ｐｈ时，收率分别为８０％、６１％、１０％和５％，并讨论了这一反应的机理。     

Structure and Reactivity of Lithium Enolates. From Pinacolone to Selective C-Alkylations of Peptides. Difficulties and Opportunities Afforded by Complex Structures

The chemistry of lithium enolates is used to demonstrate that complex structures held together by noncovalent bonds (“supramolecules”) may dramatically influence the result of seemingly simple standard reactions of organic synthesis. Detailed structural data have been obtained by crystallographic investigations of numerous Li enolates and analogous derivatives. The most remarkable features of these structures are aggregation to give dimers, tetramers, and higher oligomers, complexation of the metal centers by solvent molecules and chelating ligands, and hydrogen-bond formation of weak acids such as secondary amines with the anionoid part of the enolates. The presence in nonpolar solvents of the same supramolecules has been established by NMR-spectroscopic, by osmometric, and by calorimetric measurements. The structures and the order of magnitude of the interactions have also been reproduced by ab-initio calculations. Most importantly, supramolecules may be product-forming species in synthetic reactions of Li enolates. A knowledge of the complex structures of Li enolates also improves our understanding of their reactivity. Thus, simple procedures have been developed to avoid complications caused by secondary amines, formed concomitantly with Li enolates by the common methods. Mixtures of achiral Li enolates and chiral Li amides can give rise to enantioselective reactions. Solubilization by LiX is observed, especially of multiply lithiated compounds. This effect is exploited for alkylations of N-methylglycine (sarcosine) CH₂ groups in open-chain oligopeptides. Thus, the cyclic undecapeptide cyclosporine, a potent immunosuppressant, is converted into a THF-soluble hexalithio derivative (without epimerization of stereogenic centers) and alkylated by a variety of electrophiles in the presence of either excess lithiumdiisopropyl amide or of up to 30 equivalents of lithium chloride. Depending on the nature of the LiX additive, a new stereogenic center of (R) or (S) configuration is created in the peptide chain by this process. A structure-activity correlation in the series of cyclosporine derivatives thus available is discussed.     

Synthesis and structural characterization of carbon-centered tris(pentafluorophenyl)silyl derivatives

A general method for the synthesis of carbon-centered tris(pentafluorophenyl)silyl derivatives (RSi(C₆F₅)₃) by reaction of trichlorosilanes (RSiCl₃) with pentafluorophenylmagnesium bromide was described. The crystal structures of obtained compounds were studied by X-ray diffraction analysis (7 structures). The peculiarities of crystal packing were analyzed by means of DFT calculations.     

A novel arylation of arylacetic acid esters using tertiary arylamines and TiCl4

The reactions of arylacetic acid esters with tertiary arylamines in the presence of TiCl₄ give α-arylated products in 65-90% yields, as well as 10-20% yields of the corresponding benzidines.     

Stereoselective titanium-mediated aldol reactions of (S)-2-tert-butyldimethylsilyloxy-3-pentanone

Titanium-mediated aldol reactions based on (S)-2-tert-butyldimethylsilyloxy-3-pentanone, a lactate-derived chiral ketone, provide the corresponding 2,4-syn-4,5-syn adducts in high yields and diastereomeric ratios with a wide array of achiral and chiral aldehydes. Furthermore, spectroscopic studies of intermediates involved in the process have permitted to propose a mechanism that accounts for the experimental results.     

An unusual twist conformation of 2-O-methyl-1,3,4,5-tetrakis-O-tert-butyldiphenylsilyl-myo-inositol

The ring conformation of 2-O-methyl-1,3,4,5-tetrakis-O-tert-butyldiphenylsilyl-myo-inositol was in a twist form both in solid state and in solution. This is the first observation of a stable twist conformer induced by the introduction of bulky silyl protecting groups.     

Multifunctional coupling agents for living cationic polymerization. IV. Synthesis of end-functionalized multiarmed poly(vinyl ethers) with multifunctional silyl enol ethers

Telechelic ( 8 ) and end-functionalized four-arm star polymers ( 9 ) were synthesized through the coupling reactions of end-functionalized living poly(isobutyl vinyl ether) ( 5; DP _n ～ 10) with the bi-and tetrafunctional silyl enol ethers, H_4-nC? [CH₂OC₆H₄C(OSiMe₃) = CH₂]_n ( 3: n = 2; 4: n = 4). The precursor polymers 5 were prepared by living cationic polymerization with functionalized initiators, CH₃CH(Cl)OCH₂CH₂X(6), in conjunction with zinc chloride in methylene chloride at ?15°C. The initiators 6 were obtained by the addition of hydrogen chloride gas to vinyl ethers bearing pendant functional groups X , including acetoxy [? OC(O)CH₃], styryl (? OCH₂C₆H₄-p-CH = CH₂), and methacryloyl [? OC(O)C(CH₃) = CH₂]. The coupling reactions with 3 and 4 in methylene chloride at ?15°C for 24 h afforded the end-functionalized multiarmed polymers ( 8 and 9 ) in high yield (>91%), where those with styryl or methacryloyl groups are new multifunctional macromonomers. © 1994 John Wiley & Sons, Inc.