Benzylic carbon atom

A white solid, m.p. 178 C. Primarily of interest as a brominaling agent which will replace activated hydrogen atoms in benzylic or allylic positions, and also those on a carbon atom a to a carbonyl group. Activating influences can produce nuclear substitution in a benzene ring and certain heterocyclic compounds also used in the oxidation of secondary alcohols to ketones. 

Unfortunately this route gives only a 40% yield IJ. Amer. Cham. Soc 1951, 73, 3237) in the Grignard reaction, largely because benzyl Grignard reagents easily give radicals which polymerise. In any case, it s poor tactics to chop off carbon atoms one at a time, and a better disconnection would be ... 

The large sulfur atom is a preferred reaction site in synthetic intermediates to introduce chirality into a carbon compound. Thermal equilibrations of chiral sulfoxides are slow, and parbanions with lithium or sodium as counterions on a chiral carbon atom adjacent to a sulfoxide group maintain their chirality. The benzylic proton of chiral sulfoxides is removed stereoselectively by strong bases. The largest groups prefer the anti conformation, e.g. phenyl and oxygen in the first example, phenyl and rert-butyl in the second. Deprotonation occurs at the methylene group on the least hindered site adjacent to the unshared electron pair of the sulfur atom (R.R. Fraser, 1972 F. Montanari, 1975). 

Alkyl groups attached to aromatic rings are oxidized more readily than the ring in alkaline media. Complete oxidation to benzoic acids usually occurs with nonspecific oxidants such as KMnO, but activated tertiary carbon atoms can be oxidized to the corresponding alcohols (R. Stewart, 1965 D. Arndt, 1975). With mercury(ll) acetate, allyiic and benzylic oxidations are aJso possible. It is most widely used in the mild dehydrogenation of tertiary amines to give, enamines or heteroarenes (M. Shamma, 1970 H. Arzoumanian. 1971 A. Friedrich, 1975). 

According to Section 4.02.3.1.8 substituents removed from the pyrazole ring by two or more saturated carbon atoms and substituents on the benzene ring of indazoles are similar in reactivity to the corresponding aromatic derivatives. For instance, chloromethyl-pyrazoles are comparable to benzyl chlorides and 5-hydroxyindazoles to /3-naphthols in their reactivity. 

The modification of the Madelung indole synthesis achieved by introduction of an electron withdrawing group (EWG) at the benzylic carbon atom of the N-acylated-o-alkylanilines has been quite successful. Orlemans et al. reported that indoles were isolated in decent yields when the amides were treated with t-BuOK in THF for a period of 10 minutes at room temperature. ... 

Since l-heterobut-l-en-3-ynes are readily alkylated and functionalized at the terminal acetylenic carbon atom, their reaction with hydrazines makes it possible to introduce diverse (including functional) substituents into the pyrazole ring. For instance, from benzylated methoxybutenyne 112, isomeric 2-phenylethylpyrazoles 113 were obtained in 74% yield (81H146). 

The conclusion that the initial attack of benzyl radicals on acridine occurs at the meso-carbon atom receives further support from the... 

Substitution of more complex acids for formic acid in the last step of the purine synthesis will afford intermediates substituted on the imidazole carbon atom. Thus, condensation of diaminouracyl, 12, with phenylacetic acid gives the benzylated... 

Although the ion pairs of a-substituted benzyl anions and the corresponding cations are chiral species, which, in addition, often bear a pyramidal and hence stereogenic carbon atom, in most cases rapid racemization of the alkali and alkaline earth metal derivatives occurs in solution... 

Quinoxalines with a cychc substituent other than an unsubstituted cycloalkyl, morpholino, phenyl, or piperidino group Quinoxalines bearing a substituent with more than six carbon atoms, except for an unsubstituted benzyl or benzoyl group Quinoxalines with two or more independent functional groups on a single substituent... 

A large number of trialkylacetic acid esters have been prepared by mixed Kolbe electrolysis of ethyl malonates [164]. Crossed-coupling is also used for chain extension. Extension by two carbon atoms is achieved with benzyl succinates [153, 180-182], whereby the purification of the chain extended fatty acid is simphfied by using the benzyl half ester [181a]. 

Dimerization of a number of arylalkenes catalyzed by vitamin Bj2 and Ti(III) as reductant has been examined (Shey et al. 2002). Mechanisms were examined including the requirement of a reductant, and a reaction was proposed that involved the formation of radicals at the benzylic carbon atoms. 

The aerobic degradation of nicotine produces an A-methylpyrrolidine as the first metabolite by dehydrogenation. This is then hydroxylated at the benzylic carbon atom by an FAD-containing oxidase (Dai et al. 1968), and the y-A-methylaminobutyrate that is produced by fission of the A-methylpyrolidine ring is demethylated by an oxidase to 4-aminobutyrate (Chiribau et al. 2004). 

One interesting observation deduced from the data of Table 13 is that, despite the same diastereomeric ratio, the absolute configuration around the carbon atom of the major diastereomer changed with the electrophile used. In other words, the reactions of a-lithiobenzyl sulfoxides with 020 - and its carbonylation and carbonation proceeded with retention of configuration, while methylation with CHjl resulted in inversion . The stereochemical study of these reactions was conducted with optically active benzyl sulfoxides 42 and 39 as shown in Scheme i - - nd an interesting... 

Experimental observations,23 supported by high-level ab initio calculations, 24 indicate that two extreme resonance forms contribute to the general energy of the benzyl cation the aromatic form A, in which the positive charge is concentrated at the methylene group, and the nonaromatic, methylene arenium form B with a sp2 ipso-carbon atom and ring-localized charge (Scheme 3.13). Unlike benzyl cations of the form A, which were isolated and studied, especially by Olah and coworkers,23 compounds represented by the form B remained elusive. Thus, metal complexation... 

Benzyl and Allyl Carbon Atoms Hydrogenolysis of a carbon-heteroatom bond is extremely fast if the heteroatom is connected to allylic or benzylic carbon atoms. The benzylic compounds are used very frequently in organic chemistry as protecting groups. Because of its great importance the benzylic compounds are discussed separately in the next section. 

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