Heterocyclic cleavage

A comparison between the values of the acidity of ethynylpyrazoles and the energies of heterocyclic cleavage of the C—H bond calculated by the CNDO-2 method (75KGS821) has revealed a correlation between these values (Fig. 2). 

Aromatic and heterocyclic cleavage involves a hydrocarbon being separated from an oxygen atom, which functions to link it to another moiety of the molecule this process may lead to a decrease in the initial toxicity. The metabolic effects of microorganisms differ with the molecular configuration of the product, which affect aromatic or heterocyclic ring cleavage differently. 

In the context of mechanistic studies, the electrochemical behavior and reactions with nucleophiles of 4-chloro-2,6-diphenylpyrylium and 4-chloro(bromo)flavylium have been studied <1999CHE653>. The proposed mechanism for nucleophilic substitution in halogen-substituted pyrylium and flavylium salts passes through formation of a charge-transfer complex that is converted into an ion-radical pair by simple electron transfer. Heterocyclic cleavage of the C-halogen bond occurs at the stage of the radical or the adduct from the reaction of the pyrylium salt and the nucleophile. In this study, an amine nucleophile was used however, the data are likely relevant for other types of nucleophiles as well (Scheme 5). 

R. C. Bertelson, Photochromic processes involving heterocyclic cleavage, in Photochromism (G. H. Brown, ed.), Chap. 3, pp. 45-431, Wiley-Interscience, New York (1971). 

The quinodimethane linker 1.39 (97) was easily prepared from hydroxymethyl PS resin and anthranilic acid this linker can be used to perform hetero-Diels-Alder reactions to form condensed six-member heterocycles. Cleavage with Lewis acid-nucleophile cocktails in DCM for 16-24 h at rt produces unsubstituted or alkyl-substituted heterocycles in good yields. 

Three-membered heterocycles, cleavage of (theoretical threatment) 80BSF(2)496. 

Anderson and Webster (10) showed the pyridyl-silicon bond of 2-(trimethylsilyl)pyridine to be susceptible to cleavage by alcohol and water to form unsubstituted pyridine. Thames and coworkers (11) showed that neutral reagents, including aldehydes, acid halides, chloroformates, and anhydrides, have the ability to cleave several silicon-carbon bonds on select heterocycles (Schemes VI-VIII). However, the silicon-carbon bond of nonheterocycles is not susceptible to neutral reagent cleavage, and too, the full extent of heterocyclic cleavage reactions is not known. 

Polymerization of phosphazenes is initiated either thermally (t > 230 °C) or by the use of Lewis acids. In the former system it is belived that the heterocyclic cleavage of the P—Cl bond is followed by a nucleophilic attack of the monomer molecule leading to the phosphonium cation 4) ... 

Homogeneous dehydrogenation Aromatization of N-heterocyclics Cleavage of N-ylids... 

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