Benzylic compounds definition

For the cydative cleavage step, it turned out that aprotic conditions were definitely superior to the use of protic media. Thus, employing N,N-dimethylformamide as solvent at somewhat elevated temperatures furnished the desired compounds in high yields and excellent purities. Having established the optimized conditions, various phthalic acids and amines were employed to prepare a set of phthalimides (Scheme 7.51). However, the nature of the amine was seen to have an effect on the outcome of the reaction. Benzyl derivatives furnished somewhat lower yields, probably due to the reduced activities of these amines. Aromatic amines could not be included in the study as auto-induced ring-closure occurred during the conversion of the polymer-bound phthalic acid. 

A further aid in the location of the solvents and their exact specification is the Chemical Abstracts (CAS) Registry Number, shown in the second column. The Chemical Abstracts name may be the same as the commonly used one or may differ from it considerably, so that it is not always easy to find the solvents in these Chemical Substance Indexes of the Chemical Abstracts. Eor instance, benzene, methyl is a fairly transparent name for toluene, and methanol, phenyl a slightly less one for benzyl alcohol, but one has to become familiar with the systematics of Chemical Abstracts nomenclature in order to search for diethyl ether or any other more complicated compound. It is expected that with all this information available in table Al the solvents listed are definitely specified and readily found in the Abstracts and other compilation of information and data. 

The intermediate 1,5-dicarbonyl compounds of type 24 (Scheme 1) can be constructed not only on the basis of meta-alkoxy-substituted benzyl ketones (C4 + Ci synthesis, Section II,C), but also under definite conditions starting from aryl ketones (C2 + C3 synthesis). Thus, in a molecule of acylveratrole derivatives of type 79, the excess of 7r-electron density due to the presence of two ortho-methoxy groups allows such compounds to be involved in electrophilic substitutions with benzoin (73URP2 74KGS1575). 

As mentioned above, the photooxidation was discovered by exposure of compound 22 to sunlight. The reaction proved to be of great value for angucycline synthesis because the -hydroxy group present in most natural products which is easily eliminated under basic or acidic conditions (see Scheme 2) and the carbonyl group at C-1 can thus be introduced under mild neutral conditions. We assume that the reaction is initiated by Norrish type II y-hydrogen abstraction of the excited carbonyl in 25 to yield a diradical 26 as shown in Scheme 8 with 1-deoxyrabelomycin (25) as the example [39]. The H-abstraction requires a very definite steric environment in which the benzylic protons have to be in proximity of the excited carbonyl group. Subsequent addition of the diradical 26 with... 

Cases in which more than one tautomerizable substituent are present in the imidazole ring are common, but tautomerism studies of such compounds are less so. Work on the hydantoins (imidazolidine-2,4-diones) is not at all definitive UV and IR studies suggest the dioxo form (78), but evidence for the existence of other tautomeric structures (79,80) is not convincing (Scheme 26). ImidazoIidine-4,5-diones also exist as the dioxo forms. NMR studies show that the 2-benzyl derivatives must exist in solution as the NH form (81 R = H, Me), and the methoxy derivatives, similarly, are NH (82) rather than OH (83) derivatives (Scheme 26). 

Cyclization of amidines 1 to the corresponding quinoxalin-3-amine 1-oxides 2 can be readily achieved by reaction with bases. This ring closure occurs via deprotonation of the benzyl group and intramolecular nucleophilic addition to the nitro group giving structurally definite compounds, in contrast to the mono-A -oxidation reaction of the parent hcterocycles (sec Section6.3.2.1.4.1.). ... 

By our usual definition, benzylic and allylic sulfoxides are not aromatic. Certainly, they are not conjugated to the aryl group. However, their behavior is more related to the aromatic sulfoxides than the other aliphatic compounds. Perhaps this is because the observed a-cleavage chemistry is as related to the benzyl chromophore as it is to the sulfoxide. Nonetheless, these reactions were among the first to be studied historically, and they set precedent for the thinking of authors working in conjugated systems. 

The detection and quantification of polychlorinated dibenzo-p-dioxins, and in particular the 2,3,7,8-tetrachlorinated dibenzo-p-dioxin (2,3,7,8-TCDD), is a major application for double-focusing magnetic-sector mass spectrometers. Despite extensive clean-up procedures, samples still contain compounds such as polychlorinated biphenyls and benzyl phenyl ethers, which have the same nominal masses as the compounds of interest. The sample is spiked with a known amount of the isotope labelled form of 2,3,7,8-TCDD, introduced via gas chromatography and recorded by high-resolution mass spectrometry. The measurement is quantified by comparison of the native dioxin response to that from the C-labelled form, and verified by confirmation of the ratio of the major isotopes of both the native and the C-labelled dioxins. At 10 000 resolving power (10% valley definition) the detection level for 2,3,7,8-TCDD is about 1 femtogram, or 3 attomole (Figure 6). 

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