Synthetic methods synthesis

The most important pericyclic reaction in synthesis, indeed one of the most important of all synthetic methods, is the Diels-Alder reaction. We have seen this many times before. What are the clues for a Diels-Alder disconnection ... 

The intramolecular version for synthesizing cyclic and polycyclic compounds offers a powerful synthetic method for naturally occurring macrocyclic and polycyclic compounds, and novel total syntheses of many naturally occurring complex molecules have been achieved by synthetic designs based on this methodology. Cyclization by the coupling of an enone and alkenyl iodide has been applied to the synthesis of a model compound of l6-membered car-bomycin B 162 in 55% yield. A stoichiometric amount of the catalyst was used because the reaction was carried out under high dilution conditions[132]. 

Intramolecular allylation offers a useful synthetic method for macrocyclic compounds. An application to the synthesis of humulene (83) by the cycliza-... 

Best Synthetic Methods is now 10 years old, is a family of 16 volumes and has been well received by the majority of chemists as a valuable aid in their synthetic endeavours, be they academic or commercial. The focus of the series so far has been on special methods, reagents or techniques. This volume is the first of a new sub-series with a focus on heterocycles and their synthesis. It is amazing the extent to which each heterocyclic type has its own specialized synthetic methodology. Whether the chemist is endeavouring to make a heterocycle by ring synthesis or wishes to introduce specific substituents, it is the intention that this new development will serve their needs in a practical, authoritative, fully illustrative and compact manner. Richard Sundberg is an authority on indole chemistry and it is a pleasure to have such a noted heterocyclist to initiate this venture. 

In this section, only salient features of the synthesis, physicochemical properties, and reactivity of major derivatives of 2-aminothiazole and 2-imino-4-thiazoline are summarized. Further details on each compound are found in associated references collected in Section VII. The synthetic methods reported in this section exclude heterocydization methods treated in Chapter II but given in specific references found in Section VII. 

The reaction of phosphorus pentasulfide with a-acylamino carbonyl compounds of type Ilia also yields thiazoles. Even more commonly, a mercaptoketone is condensed with a nitrile of type IVa or a-mercaptoacids or their esters with Schiff bases. This ring closure is limited to the thiazolidines. In the Va ring-closure type, /3-mercaptoalkylamines serve as the principal starting materials, and ethylformate is the reactant that supplies the carbon at the 2-position of the ring. These syntheses constitute the most important route for the preparation of many thiazolidines and 2-thiazohnes. In the Vb t3fpe of synthesis, one of the reactant supplies only the carbon at the 5-position of the resultant thiazole. Then in these latter years new modern synthetic methods of thiazole ring have been developed (see Section 7 also Refs. 515, 758, 807, 812, 822). 

The thermal decarboxylation of malonic acid derivatives is the last step m a multistep synthesis of carboxylic acids known as the malonic ester synthesis This synthetic method will be described m Section 21 7... 

With a regioselectivity opposite to that of the Zaitsev rule the Hofmann ehmma tion IS sometimes used in synthesis to prepare alkenes not accessible by dehydrohalo genation of alkyl halides This application decreased in importance once the Wittig reac tion (Section 17 12) became established as a synthetic method Similarly most of the analytical applications of Hofmann elimination have been replaced by spectroscopic methods... 

Acetoacetic ester synthesis (Section 21 6) A synthetic method for the preparation of ketones in which alkylation of the enolate of ethyl acetoacetate... 

Ketose (Section 25 1) A carbohydrate that contains a ketone carbonyl group in its open chain form Kiliam-Fischer synthesis (Section 25 20) A synthetic method for carbohydrate chain extension The new carbon-carbon bond IS formed by converting an aldose to its cyanohydnn Reduction of the cyano group to an aldehyde function com pletes the synthesis... 

Since successful commercialization of Kapton by Du Pont Company in the 1960s (10), numerous compositions of polyimide and various new methods of syntheses have been described in the Hterature (1—5). A successful result for each method depends on the nature of the chemical components involved in the system, including monomers, intermediates, solvents, and the polyimide products, as well as on physical conditions during the synthesis. Properties such as monomer reactivity and solubiHty, and the glass-transition temperature,T, crystallinity, T, and melt viscosity of the polyimide products ultimately determine the effectiveness of each process. Accordingly, proper selection of synthetic method is often critical for preparation of polyimides of a given chemical composition. 

Cycloahphatic amine synthesis routes may be described as distinct synthetic methods, though practice often combines, or hybridi2es, the steps that occur amination of cycloalkanols, reductive amination of cycHc ketones, ring reduction of cycloalkenylarnines, nitrile addition to ahcycHc carbocations, reduction of cyanocycloalkanes to aminomethylcycloalkanes, and reduction of nitrocycloalkanes or cycHc ketoximes. 

Phytol [505-06-5] (111) and isophytol [150-86-7] (112) are important intermediates used in commercial synthesis of Vitamins E and K. There is a variety of synthetic methods for their manufacture. Chlorophyll [479-61-8] is a phytyl ester. 

Thiols can be prepared by a variety of methods. The most-utilised of these synthetic methods for tertiary and secondary thiols is acid-catalysed synthesis for normal and secondary thiols, the most-utilised methods are free-radical-initiated, alcohol substitution, or halide substitution for mercaptoalcohols, the most-utilised method is oxhane addition and for mercaptoacids and mercaptonitnles, the most-utilised methods are Michael-type additions. 

Unsymmetrical functional tetraorganotins are generally prepared by tin hydride addition (hydrostaimation) to functional unsaturated organic compounds (88) (see Hydroboration). The realization that organotin hydrides readily add to atiphatic carbon—carbon double and triple bonds forming tin—carbon bonds led to a synthetic method which does not rely on reactive organometatiic reagents for tin—carbon bond formation and, thus, allows the synthesis of... 

Synthesis. One consequence of the discovery of the carbapenem natural products has been the development of new synthetic methods, the impetus for which was provided by the exceptional antibacterial potential of the compounds coupled with the extremely poor fermentation yields. Only chemical synthesis could provide the quantities of MK 0787 (18) necessary for clinical trials and commercial production. 

Synthesis. Several synthetic methods have been reported for oxazine dyes. The following are representative ... 

General synthetic methods were developed after 1920 and extended to many new systems. Oxidative syntheses of dyes are primarily of historical interest (1), whereas nonoxidative syntheses are the most versatile and employ varied combinations of nucleophilic and electrophilic regents. One review Hsts references for the synthesis of dyes prepared before 1959 (12), and another review provides supplemental references to more recent compounds (13). Many nucleophilic and electrophilic reagents used to synthesize cyanine and related dyes are tabulated in Reference 16. 

Information on the synthesis of the polyetherimide—polysiloxane block copolymers has not been disclosed. Many other synthetic methods for preparing block copolymers have been described (19,20,25) but are currendy not beheved to be commercially important. 

Other synthetic methods have been investigated but have not become commercial. These include, for example, the hydration of ethylene in the presence of dilute acids (weak sulfuric acid process) the conversion of acetylene to acetaldehyde, followed by hydrogenation of the aldehyde to ethyl alcohol and the Fischer-Tropsch hydrocarbon synthesis. Synthetic fuels research has resulted in a whole new look at processes to make lower molecular weight alcohols from synthesis gas. 

The first primary synthesis of a pyrimidine from aliphatic fragments was carried out by Frankland and Kolbe in 1848. Since then, a great many quite distinct primary synthetic methods have been devised, although it is true to say that one of these (the Principal Synthesis ) has provided upward of 80% of all known pyrimidines, either directly or indirectly. 

D. Seebach, R. Imwinkelried, and T. Weber, EPC Synthesis With C,C Bond Formation via Acetals and Enimines, in Modern Synthetic Methods 1986, Vol. 4, R. Scheffold, Ed., Springer-Verlag, New York, 1986, p. 125. 

Methyl ketones are important intermediates for the synthesis of methyl alkyl carbinols, annulation reagents, and cyclic compounds. A common synthetic method for the preparation of methyl ketones is the alkylation of acetone derivatives, but the method suffers limitations such as low yields and lack of regioselectivity. Preparation of methyl ketones from olefins and acetylenes using mercury compounds is a better method. For example, hydration of terminal acetylenes using HgSO gives methyl ketones cleanly. Oxymercuration of 1-olefins and subsequent oxidation with chromic oxide is... 

Synthesis of the title compound is representative of a number of syntheses of nonaromatic nitrogen heterocycles via Pd(Ill-catalyzed amination of olefins. These tosylated enamines are not readily available by standard synthetic methods, and show potential for further functionalization of the heterocycle. The saturated amine can be synthesized from the title compound by hydrogenation of the double bond followed by photolytic deprotection. ... 

Part Two, a collection of multistep syntheses accomplished over a period of more than three decades by the Corey group, provides much integrated information on synthetic methods and pathways for the construction of interesting target molecules. These syntheses are the result of synthetic planning which was based on the general principles summarized in Part One. Thus, Part Two serves to supplement Part One with emphasis on the methods and reactions of synthesis and also on specific examples of retrosynthetically planned syntheses. 

Recent Synthetic Methods for Polyfluoro-aromatic Compounds Yakobson, G G, Vlasov, V M Synthesis 652-672 220... 

The synthetic method used to accomplish this is an indirect one known as hydroboration-oxidation. It was developed by Professor Herbert C. Brown and his coworkers at Purdue University in the 1950s as part of a broad progran designed to apply boron-containing reagents to organic chemical synthesis. The number of applications is so large (hydroboration-oxidation is just one of them) and the work so novel that Brown was a corecipient of the 1979 Nobel Prize in chemistry. 

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