General and Synthetic Methods: Volume 5 (Specialist Periodical Reports, Band 5) - Hardcover

Hardcover

ISBN 10: 0851868649 ISBN 13: 9780851868646

Verlag: Royal Society of Chemistry, 1982

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Specialist Periodical Reports provide systematic and detailed review coverage of progress in the major areas of chemical research. Written by experts in their specialist fields the series creates a unique service for the active research chemist, supplying regular critical in-depth accounts of progress in particular areas of chemistry. For over 80 years the Royal Society of Chemistry and its predecessor, the Chemical Society, have been publishing reports charting developments in chemistry, which originally took the form of Annual Reports. However, by 1967 the whole spectrum of chemistry could no longer be contained within one volume and the series Specialist Periodical Reports was born. The Annual Reports themselves still existed but were divided into two, and subsequently three, volumes covering Inorganic, Organic and Physical Chemistry. For more general coverage of the highlights in chemistry they remain a 'must'. Since that time the SPR series has altered according to the fluctuating degree of activity in various fields of chemistry. Some titles have remained unchanged, while others have altered their emphasis along with their titles; some have been combined under a new name whereas others have had to be discontinued. The current list of Specialist Periodical Reports can be seen on the inside flap of this volume.

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General and Synthetic Methods Volume 5

A Review of the Literature Published During 1980

By G. Pattenden

The Royal Society of Chemistry

Copyright © 1982 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-0-85186-864-6

Contents

Chapter 1 Saturated and Unsaturated Hydrocarbons By J. M. Clough, 1, 
Chapter 2 Aldehydes and Ketones By S. C. Eyley, 59, 
Chapter 3 Carboxylic Acids and Derivatives By D. W. Knight, 100, 
Chapter 4 Alcohols, Halogeno-compounds, and Ethers By R. C. F. Jones, 148, 
Chapter 5 Amines, Nitriles, and Other Nitrogen-containing Functional Groups By G. Kneen, 183, 
Chapter 6 Organometallics in Synthesis Part I The Transition Elements By S. v. Ley and R. A. Porter, 208, 
Chapter 7 Saturated Carbocyclic Ring Synthesis By A. J. Barker, K. Cooper, and G. Pattenden, 257, 
Chapter 8 Saturated Heterocyclic Ring Synthesis By R. C. Brown and A. H. Ingall, 288, 
Chapter 9 Strategy and Design in Synthesis By A. P. Johnson, 387, 
Author Index, 419, 

CHAPTER 1

Saturated and Unsaturated Hydrocarbons

BY J. M. CLOUGH

1 Saturated Hydrocarbons

Many new methods for the preparation of alkanes by reductive removal of functional groups have been reported during the year. Barton and his co-workers have presented a new radical decarboxylation for the conversion of carboxylic acids into hydrocarbons. Following esterification with trans-9-hydroxy-10-phenylthio-(or -10-chloro-)9, 10-dihydrophenanthrene, a primary, secondary, or tertiary carboxylic acid is smoothly reduced under neutral conditions by tri-n-butylstannane and a radical initiator (e.g. Scheme 1). Formation of phenanthrene as by-product provides the driving force for the fragmentation. Another new method for the degradation of carboxylic acids to the corresponding nor-alkanes using the same stannane and radical initiator, but in this case via their phenylselenoesters, has been outlined briefly.

Aldehydes are decarbonylated catalytically using solutions of bis(triphenylphosphine)(tetraphenylphorphyrinato)ruthenium(II) at, or slightly above, room temperature. Decarbonylation of aromatic aldehydes takes place in high yield, but some aliphatic aldehydes give significant amounts of rearranged products.

The nitrile group of 4-cyanopyridine is replaced quantitatively by hydrogen when treated with titanium trichloride in aqueous acetic acid. Under the same conditions, 2-cyanopyridine undergoes reductive decyanation only in poor yield, and 3-cyanopyridine is inert. Highly dispersed potassium on neutral alumina, easily prepared by melting potassium over alumina in an inert atmosphere, effects reductive cleavage of the cyano-group of alkyl nitriles in hexane at room temperature (e.g. Scheme 2). Alternatively, activated tertiary or secondary nitriles can be efficiently decyanated by heating with molten potassium hydroxide. By contrast, aromatic and tertiary cyano-groups of relatively volatile species are transformed into methyl groups by hydrogenolysis in the gas phase over 30% nickel on alumina (52 — 99%). However, nitriles with a -hydrogen atoms undergo predominant decyanation under the reaction conditions, and other functional groups, if present, tend to be removed.

Aryl aldehydes and mono- or di-aryl ketones are conveniently reduced to arylmethanes under neutral conditions by refluxing with a five-fold excess of W-7 Raney nickel in 50% aqueous ethanol. Methoxy-, hydroxy-, carboxy-, methoxycarbonyl, or dimethylamino-groups remain unaffected, though nitro-, cyano-, and halogeno-groups are reduced under the reaction conditions. Saturated ketones, derivatized as toluene-p-sulphonylhydrazones, are reduced to alkanes in high yield within two hours by bis(triphenylphosphine)copper(I) tetrahydroborate in refluxing chloroform. The method gives lower yields with aldehydes, and is not effective for the decarbonylation of aromatic or α,β-unsaturated carbonyl compounds. In a still milder procedure, the same reducing agent reacts with 2,4,6-tri-isopropylhydrazones (trisylhydrazones) to give alkanes in moderate yield at room temperature. Ethylene thioacetals are com- pletely desulphurized to hydrocarbons by four molar equivalents of tri-n-butyltin hydride and catalytic amounts of 2,2'-azobis(isobutyronitrile).

Selenium is smoothly extruded from dibenzyl selenides at 600°C to give high yields of bibenzyl and elemental selenium. Unsymmetrically substituted dibenzyl selenides give mixtures of the three possible bibenzyls, suggesting that the reaction proceeds via free benzyl radicals.

A direct deoxygenation of alcohols that are capable of forming relatively stable carbanions has been reported. The alcohol reacts with potassium to form its alkoxide, which is treated with pentacarbonyliron; acidic work-up furnishes the alkane (43 — 90%) together with dimerized and dehydrated products in some cases.

A much improved method for the replacement of phenolic hydroxy-groups by hydrogen has been reported. 2-Phenyltetrazolyl ethers [e.g. (1)], easily pre- pared from phenols, are now shown to be cleaved reductively by catalytic transfer hydrogenation within two hours at room temperature in a two-phase solvent system (e.g. Scheme 3).

Alper and his co-workers have reported two new methods for the desulphurization of aliphatic, aromatic, and benzylic thiols. In one method thiols are treated with hexacarbonylmolybdenum, either in acetic acid or following pre-adsorption on silica. An alternative and milder procedure uses anhydrous ferrous chloride and sodium triethylhydroborate in THF at –78°C. The 2-benzothiazolylthio-group, useful for stabilizing carbanions, is conveniently removed by electroreduction at a carbon electrode in a cathode cell (e.g. Scheme 4).

Brown and his co-workers have compared representative simple and complex metal hydrides in order to assess their capabilities for the hydrogenolysis of alkyl halides. Of the reducing agents studied, lithium triethylborohydride is the most powerful, and is the reagent of choice for the hydrogenolysis of alkyl iodides, bromides, and chlorides. Weaker reagents offer the possibility of selective hydrogenolysis. β-Hydroxy-bromides and -iodides, protected as their tetrahydropyranyl ethers, are dehalogenated in practically quantitative yields by chromium(II)-catalysed electrochemical reduction. The method can be used to prepare deoxy- from halogenodeoxy-nucleosides. The use of chlorotrimethyl-silane and sodium iodide in acetonitrile constitutes a new mild and simple method for the dehalogenation of a-halogeno-ketones in high yields. 2',3',5'-Tri-O-acetyl-6-bromotoyocamycin (2) is reductively debrominated in 60% yield by a mixture of N,O-bis(trimethylsilyl)acetamide (BSA), potassium fluoride, and dicyclohexyl-18-crown-6 in refluxing acetonitrile. Other brominated purine and purine-like nucleosides are debrominated in the same way.

It has been shown that the nature of the solvent can dramatically change the chemoselectivity of reduction by a complex metal hydride. Thus lithium aluminium hydride in diethyl ether rapidly and selectively reduces alkyl tosylates to the corresponding alkanes in the presence of alkyl iodides and bromides without concurrent attack on the halogen; in diglyme the selectivity is reversed.

Di-isobutylaluminium hydride is an effective reagent for removing tosyl groups from tetrahydrobenzo[b]thiophens and other thiophen-containing species which are sensitive to methods described...

Details zur Ausgabe

• Verlag: Royal Society of Chemistry
• Erscheinungsdatum: 1982
• Sprache: Englisch
• ISBN 10: 0851868649
• ISBN 13: 9780851868646
• Einband: Gebundene Ausgabe
• Anzahl der Seiten: 456
• Herausgeber: Pattenden G.
• Kontakt zum Hersteller: Nicht verfügbar
• Verantwortliche Person: GPSR Kontakt; gpsr@libri.de; ; Friedensallee 273; Hamburg; 22763; Deutschland