Subject reaction with carbonate radical

The lack of reactivity of 3-halo substituents under non-radical nucleophilic substitution conditions allows differential functionalization of pyri-dines by 3-umpolung and 2-nucIeophilic substitution processes. Thus, treatment of 2-fluoro-3-iodopyridine (189) with oxygen or amine nucleophiles affords products 191 which, upon subjection of SRN1 reactions with carbon, phosphorus, and sulfur systems, give 2,3-difunctionalized pyri-dines 192 (Scheme 56) (88JOC2740). 

The reaction with carbon tetrahalides [213] probably involves free-radical attack e.g. by CBra) rather than electrophilic attack on the enol, but is still subject to selection of the reaction site leading to the more stable conjugated product (c/. p. 159). The reaction with methyl chloride (and a base) has been described only in a patent [214], and no mechanistic details are available. It is surprising that so unreactive an electrophile should attack the enol ether. There is no clear reason for chloromethylation favouring C(4), beyond the suggestion [21 ] that the reagent may first form a complex with the 3-acetoxy group. 

Evidence strongly supporting this latter mechanism was obtained by Cadogan and Foster, who subjected jSjS-dimethylphenylethyl diethyl phosphite and benzyl diethyl phosphite to peroxide-catalyzed reaction with carbon tetrachloride. These workers showed by careful gas chromatography the absence of any products expected from the rearrangement, dimerization or disproportionation of free /3j(3-dimethyl-phenylethyl (PhCMe2CH2 ) or benzyl radicals. 

In ambient air, the primary removal mechanism for acrolein is predicted to be reaction with photochemically generated hydroxyl radicals (half-life 15-20 hours). Products of this reaction include carbon monoxide, formaldehyde, and glycolaldehyde. In the presence of nitrogen oxides, peroxynitrate and nitric acid are also formed. Small amounts of acrolein may also be removed from the atmosphere in precipitation. Insufficient data are available to predict the fate of acrolein in indoor air. In water, small amounts of acrolein may be removed by volatilization (half-life 23 hours from a model river 1 m deep), aerobic biodegradation, or reversible hydration to 0-hydroxypropionaldehyde, which subsequently biodegrades. Half-lives less than 1-3 days for small amounts of acrolein in surface water have been observed. When highly concentrated amounts of acrolein are released or spilled into water, this compound may polymerize by oxidation or hydration processes. In soil, acrolein is expected to be subject to the same removal processes as in water. 

A radical cascade reaction has been accompHshed by StaHnski and coworkers which converts dipeptide derivatives to nitrogen-containing heterocycles (Scheme 6) [9]. In this work, N-bromobenzyl-hf-propargyl-substituted dipeptides such as 10 were subjected to Stork s catalytic procedure with tributyltin hydride [10]. An aryl radical is formed followed by a 1,5-hydrogen shift, generating the a-centered carbon radical 11. 5-Fxo-dig radical cyclization... 

Three studies on radical cations discuss the characterization of polynuclear aromatic radical cation salts as organic metals (8), the reactions of cation radicals with neutral radicals (9), and the magnetic-electrical properties of perfluoroaromatic radical-cation salts (10). Chapters on polynuclear aromatic compounds in nonvolatile petroleum products (II) and in coal-based materials (12) present reviews of the subject and new findings. The remaining chapters in this book discuss the thermal conversion of polynuclear aromatic compounds to carbon (13), the nitration of pyrene by mixtures of N02 and N204 (14), the spectra, structures, and chromatographic retention times of large polycyclic aromatic hydrocarbons (15), the desulfurization of polynuclear thiophenes correlated with tt electron densities (16) and simple theoretical methods to predict and correlate polynuclear benzenoid aromatic hydrocarbon reactivities (IT). 

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