Group abstract

Sometimes it is useful to be able to remove a protecting group by photolysis. 2-Nitrobenzyl carbamates meet this requirement. The photoexcited nitro group abstracts a hydrogen from the benzylic position, which is then converted to a a-hydroxybenzyl carbamate that readily hydrolyzes232... 

The proposed mechanism starts with a methyl group abstraction on platinum complex 416 with the borane reagent in the presence of diyne 414 (Scheme 105). The square-planar cationic diyne-platinum(n) complex 417 is converted to the octahedral platinum(rv) hydride intermediate 418 through oxidative addition of the hydrosilane. This complex decomposes rapidly with methane release to form another tetracoordinated platinum(n) species 419, followed by platinasilylation of the triple bond. The resulting vinylplatinum 420 undergoes an intramolecular carboplatination to... 

Fig. 19 Another proposed mechanism of peptide synthesis catalyzed by the ribosome. The P-site 2 -OH group abstracts a hydrogen from the amino group [161]...

Takada M, Fukuoka M, Furuse K, et al. A Phase III study of concurrent versus sequential thoracic radiotherapy in combination with cisplatin and etoposide for limited-stage small-cell lung cancer preliminary results of the Japan Clinical Oncology Group (abstract 1103). ProcAm Soc Clin Oncol 1996 15 372. 

D. E. Williams and J. P. Cannady, Analysis of polymer surface functional groups. Abstracts, 182nd ACS National Meeting, p. 1NDE-23 (1981). 

A second basic interaction pathway between transition metal complexes and organic substrates is SET (Path B). The overall processes can involve one individual or several sequential SET steps. For the latter, timing and direction of SET steps determine the reaction outcome significantly. The catalyzed reaction can proceed either as redox-neutral processes, in which oxidative and reductive SET steps are involved in the catalytic cycle, or as overall oxidative or reductive catalytic reactions, where two oxidative or reductive SET steps occur consecutively in the catalytic cycle. The third pathway (Path C) consists of a direct atom or group abstraction by the metal complex, which is possible for a weak R-X bond. 

The formation of an alkyl radical resulting from the initial atom (or group) abstraction by (TMS)3Si radical or by addition of (TMS)3Si to unsaturated bonds is often designed so that this intermediate can undergo a number of consecutive reactions. 

Hofmann elimination of exhaustively methylated butan-2-amine. The most stable conformation of the C2—C3 bond has no proton on C3 in an anti relationship to the leaving group. Along the Cl —C2 bond, however, any staggered conformation has an anti relationship between a proton and the leaving group. Abstraction of a proton from Cl gives the Hofmann product. 

It is unusual to think of a carbonyl compound as an acid, but the protons a to a carbonyl group can be removed by a strong base. Protons a to two carbonyl groups are even more acidic in some cases, acidity approaches that of phenols. This acidity is the basis for a-substitution reactions of compounds having carbonyl groups. Abstraction by base of an a proton produces a resonance-stabilized enolate anion that can be used in alkylations involving alkyl halides and tosylates. 

The likely pathway of photochemical cleavage is a Norrish type II cleavage reaction (Scheme 17.1). During the photoisomerization, the activated oxygen of the nitro group abstracts a y-hydrogen from the benzylic position to produce a quinone methide-like intermediate, which subsequently rearranges to afford an o-nitrosobenzaldehyde and thereby releases the carboxylic acid product. 

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