Neighbouring-group participation

There is some evidence for the formation of unstable benzazetidines from [2 + 2] cycloaddition of benzyne to imines (75BCJ1063). A novel formation of a benzazetidine is reported in the solvolysis of the exo iV-chloro compound (297). Neighbouring group participation by the benzene ring leads to the cation (298), which is intercepted by methanol to give the benzazetidine (299) (81CC1028). 

Sulphoxides with -carboxylic acid or amide groups are converted, in nearly quantitative yields, to the sulphone whilst other acids and amides did not show oxidation. In the cases where oxidation did occur, the acid group was converted to the acid chloride (equation 31) whilst the amide was converted to the nitrile (equation 32). These results indicate that neighbouring-group participation in the case of carboxylic acids and amides occurs only when a five-membered intermediate is formed. In the case of hydroxyl groups, four-, five-or six-membered intermediates are favourable. 

B. Solvolysis of Phosphoric Acid Derivatives.—Interest continues in neighbouring-group participation in the solvolysis of phosphate esters. As a potential model compound for investigating the mechanism of ribo-nuclease action, the phenyl hydrogen phosphate ester of c/j-3,4-tetrahydro-furandiol (24) has been the subject of a detailed study. Above (and probably also below) pH 4 hydrolysis gives solely the cyclic phosphate (25)... 

Hesse691 has shown that the unimolecular chemistry of cation radicals of di- or polyfunctionalized alkanes is strongly dependent upon the interaction of the functional groups, mainly via neighbouring group participation in the transition states and the... 

This neighbouring group participation by bromine (cf. p. 93) does not of course prove that addition to alkenes proceeds via cyclic bromonium ions, but it does mean that such species are no longer merely ad hoc assumptions, and to that extent are correspondingly more plausible as intermediates. 

Ester hydrolysis, neighbouring group participation by carbonyl groups in, 28, 171... 

Neighbouring group participation by carbonyl groups in ester hydrolysis, 28, 171 Nitration, nitrosation, and halogenation, diffusion control and pre-association in, 16, 1 Nitrosation, mechanisms, 19, 381... 

Neighbouring Group Participation by Carbonyl Groups in Ester Hydrolysis... 

Capon, B. and McManus, S. P. (1976). Neighbouring Group Participation, Vol. 1. Plenum Press, New York... 

A similar ATI-bridged ONO-trident 151 was formed from the reaction of 7-oxabenzo norbomadiene 36 with the O-bridged A -methoxymethyl aziridine 146. However, in light of the bridged products discussed below, the mechanism for formation of the NH-compound may implicate neighbouring group participation of the O-bridge and a cyclic intermediate such as 150. 

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