Dehalogenation heterocycles

Microsomal oxidations may be subdivided into aromatic hydroxylation aliphatic hydroxylation alicyclic hydroxylation heterocyclic hydroxylation N-, S-, and O-dealkylation N-oxidation N-hydroxylation S-oxidation desulfuration deamination and dehalogenation. 

Table 13. Formation of Fluorinated Unsaturated Heterocyclic Compounds by Dehalogenation...

Iron carbonyls also mediate the cycloaddition reaction of allyl equivalents and dienes. In the presence of nonacarbonyldiiron a,a -dihaloketones and 1,3-dienes provide cycloheptenes (Scheme 1.5) [14,15]. Two initial dehalogenation steps afford a reactive oxoallyliron complex which undergoes a thermally allowed concerted [4 + 31-cycloaddition with 1,3-dienes. The 1,3-diene system can be incorporated in cyclic or heterocyclic systems (furans, cyclopentadienes and, less frequently, pyrroles). Noyori and coworkers applied this strategy to natural product synthesis, e.g. a-thujaplicin and P-thujaplicin [14, 16]. 

Adrian N. R. and Suflita J. M. (1990) Reductive dehalogenation of a nitrogen heterocyclic herbicide in anoxic aquifer slurries. Appl. Environ. Microb. 56(1), 292-294. 

Silver electrodes have been employed in form of an expanded silver sheet on a plastic plate in the dehalogenation of polyhalogenated heterocyclic compounds examples are given in Chapter 18. 

The removal of a halogen from an aromatic heterocycle takes place more readily than the hydrogenolysis of a phenyl halide of the same type (Eqn. 20.61). 45 The relative difference between the ease of dehalogenation of a phenyl and a heterocyclic halide is more pronounced over Raney nickel in basic medium than it is over palladium (Eqn. 20.62). 46... 

Chlorinated N,S-heterocycles, synthesis via dehalogenation by sulfur action 85S586. 

Hydrolysis of esters and ethers, hydrolytic cleavage of C—N single bonds, hydrolytic cleavage of nonaromatic heterocycles, hydration and dehydration at m ultiple bonds, new atomic linkages resulting from dehydration reactions, hydrolytic dehalogenation removal of hydrogen halide molecules, various reactions. 

Some heterocyclic aryl halides are very likely to dehalogenate. In the case of oligothiophenes, the halogenation was highly dependent on small changes of the electronic structure of the aryl halide [87]. The side reaction was suppressed by adjusting the basicity of the reaction mixture. In other cases an alternative StiUe protocol was found [88]. 

Stille coupling on heterocycles prone to dehalogenation (Scheme 18) [88] General NMP is distilled over CaHi under Ar at 20 Torr. Resins bearing... 

Chloroarenes were efficiently hydrodechlorinated with a [RhCl2HL2] (L = PCy3 or Pz Pr3) catalyst in biphasic systems under mild conditions [267], The catalyst tolerates the presence of a variety of functional groups (R, OR, CF3, COAr, COOH, NH2). Some chloro heterocycles (e.g. 5-chloro-l-ethyl-2-methylimidazole) can be readily dehalogenated, but 2-chlorotiophene does not react at all. 

Dichloropyrido[3,2- /]pyrimidine is dehalogenated by Adams catalyst in ethanol at room temperature and 1 atmosphere of hydrogen pressure, but the parent heterocycle appears to be unstable a picrate (mp 191 C) was isolated.77... 

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