Bredereck-Synthese

Die Bredereck-Synthese (s.a. Bd. VII/2c, S. 2239 Bd. XI/1, S. 659) ist eine einfache und breit anwendbare Methode zur Herstellung von in 2-Stellung unsubstituierten Imidazolen aus -Hydroxy- oder a-Halogen-ketonen durch Umsetzung mit Formamid44. 

Similar enamine cyclization processes occur in several other successful heterocycle syntheses, e.g. in the Fischer indole synthesis. In this case, however, a labile N—N bond of a l-aryl-2-vinylhydrazine is cleaved in a [3,3]-sigmatropic rearrangement, followed by cyclization and elimination of ammonia to yield the indole (B. Robinson, 1963, 1969 R. J. Sundberg, 1970). Regioselectivity is only observed if R2 contains no enolizable hydrogen, otherwise two structurally isomeric indoles are obtained. Other related cyclization reactions are found in the Pechmann synthesis of triazoles (T.L. Gilchrist, 1974) and in G. Bredereck s (1939) imidazole synthesis (M.R. Grimmett, 1970). 

Jachimowicz claimed to have synthesized 5-phosphoadenosine (in poor yield) by direct phosphorylation of adenosine with phosphorus oxychloride in pyridine, but Bredereck showed that a mixture of phosphoric esters of adenosine actually results, as might have been anticipated. Levene and Tipson succeeded in synthesizing 5-phospho-adenosine (in poor yield) by phosphorylation of 2,3-diacetyl-adenosine to give AT-phos-pho 5-phospho-2,3-diacetyl-adenosine, followed by deacetylation by alkali, and removal by acid-hydrolysis of the labile phospho group attached to nitrogen. (This synthesis was confirmed by Bredereck, et al. ) In a similar manner they phosphorylated 2,3-isopropylidene-adenosine to iV,5-di-phospho-2,3-isopropylidene-adenosine from which the acid-labile iV-phospho and isopropylidene groups were hydrolyzed, giving 5-phospho-adenosine. 

Method (iv).—Another possible way of synthesizing cord factor is to react the 2,3,4,2, 3, 4 -hexa-0-acetyl-6,6 -dideoxy-6,6 -diiodotrehalose (13), already described by Bredereck, with the silver salt of a mycolic acid deacetylation of the hexa-0-acetyl-6,6 -di-0-mycoloyltrehalose thus obtained gives cord factor. ... 

Bredereck, H, Wagner, A, Faber, G, Ott, H, Rauther, J, Eine vereinfachte Oligosaccharid-Synthese, Chem. Ber., 92, 1135-1139, 1959. 

The chemistry of 1,3,5-triazines, cyanuric acid, and cyanuric halides has been reviewed by Bann and Miller <58CRV131>, by Matsui <59YGK528>, and extensively by Smolin and Rapoport . Syntheses of 1,3,5-triazine and substituted 1,3,5-triazines have been reviewed by Bredereck... 

Probably the most valuable advance in the field of oxazole syntheses has come from the methods developed by Bredereck and his co-workers.92-94 The so-called formamide synthesis of Bredereck et al. involves, especially in this case, the interaction of a-halo ketones with formamide and usually results in high yields of oxazoles (50-70%). 

This method is not suited to the preparation of 2-unsubstituted oxazoles the main difficulty is the preparation of the acyloin formates themselves. Bredereck and Gompper94 introduced a new method of synthesizing the acyloin formates (54) by the treatment of acyloins in formic acid solution in the cold with either phosphorus trichloride or thionyl chloride. The yields in the three reported cases are 61-91%. These a-formyloxy ketones on boiling with formamide in formic acid afford the corresponding oxazoles. unsubstituted in the 2-position, in 61-75% yields.94... 

Bredereck et al. (2011) synthesized aquasols containing silica nanoparticles with diameters of 75-95 nm obtained directly by hydrolysis of 2 wt% TEOS in water in the presence of a nonionic surfactant and used Si MAS NMR spectroscopy of the freeze-dried particles to obtain information about the degree of condensation and the ratio of free hydroxyl groups. This is a typical example of the use of NMR spectroscopy as a tool in analytical chemistry of solids. 

Three syntheses of the pseudoguaianolide ( )-confertin have appeared. Schultz uses the oxidation of an a-trimethylsilylated furan intermediate followed by reduction to give a butyrolactone during his synthesis. In another, the lactone (216), prepared by iodolactonization of the appropriate dimethyl amide, is converted into (217), using Bredereck s reagent (Scheme 114). In the third... 

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