Telescoping synthesis

Synthesis gas is obtained either from methane reforming or from coal gasification (see Coal conversion processes). Telescoping the methanol carbonylation into an esterification scheme furnishes methyl acetate directly. Thermal decomposition of methyl acetate yields carbon and acetic anhydride,... 

Large-Scale Synthesis of Thienobenzazepine Derivatives Using Two Efficient Metal Catalyzed Processes Telescoped Nitro Reduction and Intramolecular Aminocarbonylation... 

In this chapter we describe a novel, safe and efficient large-scale synthetic approach to tricycle thienobenzazepines. The key steps in the synthesis include a chemoselective hydrogenation of an aryl-nitro functionality in the presence of a 3-bromo thiophene and a subsequent palladium-catalyzed intramolecular aminocarbonylation telescoped sequentially after simple catalyst and solvent exchange. 

In summary, we have described a novel and efficient synthesis of thienobenzazepine derivatives in which the key transformation includes a telescoped process involving a selective intro reduction followed by palladium-mediated intramolecular amidation. The process developed is quite amenable for preparative scale (multi-gram) and presents significant advantage to those reported previously with respect to overall yield (e.g., 50% vs. 17% overall yield), total number of synthetic transformations (4 vs. 9), and reagents and/or conditions that are suitable for large-scale synthesis. 

Elemental abundances were determined by spectral synthesis of individual lines, compared to observed spectra obtained with the FEROS spectrograph at the ESO-1.5m telescope. 

At the end of the synthesis reactions, the product can be pumped to another vessel or container via transfer lines. If the chemical reactions proceed to completion with negligible trace quantities of impurities, the next stage of production may commence in the same reaction vessel with addition of fresh raw materials. This process is called telescoping. 

Direct reduction of an aldehyde or ketone to the corresponding ether could potentially telescope two reactions, reduction and protection, into one step. S. Chandrasekhar of the Indian Institute of Chemical Technology, Hyderabad, reports (Tetrahedron Lett. 2004,45,5497) that in the present of polymethylhydrosiloxane (PMHS) and catalytic B(C6F,), TMS ethers of alcohols will convert aldehydes to the corresponding dialkyl ethers. The reaction works well for both saturated and benzylic alcohols. This may prove to be a useful alternative to Williamson synthesis for the preparation of complex ethers. 

Carbon-carbon bond formation is fundamental to all of organic chemistry. The emphasis this week is on recently-developed useful transformations that are easily scalable. Notably, these transformations telescope two or more synthesis steps into one-pot procedures. 

Shell produces 1,3 PD from ethylene oxide via hydroformylation with synthesis gas (Fig. 8.8 b). The transformation required two separate steps in the past [55], but has been improved [56], which made the large-volume use of 1,3PD in poly(trimethylene terephthalate) economically viable, and the two steps have been telescoped into one [57, 58]. Shell has a capacity to 70 kt a-1 [59]. 

Alternatively CO, obtained directly by the irradiation of (in the presence of 2% O ) with 15 MeV protons, was mixed with an equal volume of Clj and the mixture exposed over fifteen minutes to u.v. light. The radiochemical yield was about 75% [275]. Since the total time required to obtain COClj for further synthetic use is about thirty minutes, attempts were made to telescope the synthesis by combining the production of the labelled CO and the radiation-induced reaction with Cl, in one step. 

The choice of the carboxylic acid blocking group (R in Scheme 11.2) is very important, as it not only has to survive multiple reactions, it also has to be readily and cleanly removed at the end of the synthesis during the formation of the penultimate intermediate. In addition, there is an important third factor. The physical properties of the isolated intermediates need to be considered. The ideal blocking group will confer sufficient crystallinity on the key intermediates that they can easily be isolated as fairly pure defined compounds from the telescoped reaction sequences needed for commercial efficiency. 

Alpher s preference is clearly conditioned by cosmology rather than science, but in the event it led to the total elimination of the equilibrium model from subsequent enquiry. A complicating factor in the argument is the continuously changing evidence provided by astronomical observation, in both theories, the success is measured in terms of predicted nuclear abundances and invariably these predictions depend on the nature and characteristics of known types of star, assumed as the seat of nucleogenesis. As more powerful telescopes identify new types of heavenly body, new possibilities of nuclear synthesis open up and the model has to be reworked. This process continues for the a — /d — 7 model only. The equilibrium model was abandoned before the discovery of quasars and black holes, that obviously provide more attractive environments for nuclear synthesis. The only mechanism for the dispersal of freshly synthesized material is still assumed to be supernovae and this assumption could also stand reassessment. 

An interferometer can be basically described as an instrument that measures the interference of an electromagnetic field. The advantage of interferometers over other instruments when measuring astronomical sources is the angular resolution achievable, providing means to address certain scientific questions not available to single aperture telescopes. In this Section the basic principles and characteristics of an ideal stellar interferometer are presented, as well as the interferometric observables and its synthesis (Born and Wolf 1999 Monnier 2003 Quirrenbach 2001). 

Taber, G. P. Pfisterer, D. M. Colberg, J. C. A New and Simplified Process for Preparing N-[4-(3,4-Dichlorophenyl)-3,4-dihydro-l(2H)-naphthalenyl-idene]methanamine and a Telescoped Process for the Synthesis of (IS-cis)-4-(3,4-Dichlorophenol)-1,2,3,4-tetrahydro-N-methyL 1 -naphthalenamine Mandelate Key Intermediates in the Synthesis of Sertraline Hydrochloride. Org. Proa Res. Dev. 2004, [Pg.431]

Ryle, Sir Martin (1918-84) British radio astronomer, who became professor of radio astronomy at Cambridge University in 1959. He organized three surveys of celestial radio sources and developed the technique of aperture synthesis (seeradio telescope). In 1974 he shared the Nobel Prize tor physics with Antony Hewish (1924- ), who led the team that discovered pulsars. 

Write out set of complete balanced chanical equations for each reaction in the plan showing stmetnres, stoichiometric coefficients, and MWs of all reagents, target product, and byproducts. Note which intermediates are isolated and assign individual reaction yield performances accordingly. Note reaction steps that are telescoped, that is, those that involve sequential ch ical transformations without isolation of intermediate products. Note the number of branches involved in the synthesis plan. 

Telescoping A synthesis tactic often used in process chemistry that involves concatenation of reaction steps so that reaction intermediates are not isolated this is an effective optimization strategy that reduces solvent demand. 

Continuous microreactor systems have gained a lot of interest in the field of organic synthesis as these possess enhanced mass and heat transfer properties. Microreactor technology also offers a contemporary way of conducting chemical reactions In a more sustainable fashion due to the miniaturization and increased safety, and also In a technically improved manner due to intensified process efficiency. Recent developments in this area related to the synthesis of heterocyclic compounds are recorded in this chapter. Also, telescoping, in which several subsequent reaction steps (with or without purification) can be achieved by connecting different reactors to each other, is covered. 

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