Nucleophilic displacement of halogen from

Intramolecular nucleophilic displacements of halogen from u> -halohexylamines is an obvious route to saturated azepines and was the route by which hexamethyleneimine was first prepared. The method has since been superseded as a route to simple hexamethyl-eneimines but is still used for highly substituted derivatives (67MI51600). However, high dilution techniques are necessary in order to avoid polymerization intermolecular N-alkylations are minimized by using amine protecting groups, e.g. Af-tosyl. 

As in synthesis of 7r-bonded divalent compounds, the principal method of synthesis is nucleophilic displacement of halogen from the divalent metal halide as shown in Eq. (34). 

Nucleophilic Displacement of Halogen from Fluorocarbon Systems... 

The iV-oxide function enhances the rate of nucleophilic displacement of halogen from a- and y-positions. The relative rates 4 > 2 > 3 found for pyridines are echoed for the A-oxides (but signihcantly are 2 > 4 > 3 in pyridinium salts). 

Instances of nucleophilic displacement of halogen from halogeno-l,2,6-thiadiazine systems are... 

The chemistry of 2-chloro- and 2,3-dichloroquinoxalines has been previously reviewed in Simpson s monograph/ The present review further demonstrates the extensive use which these derivatives have found in the preparation of other quinoxalines. This is a result of the ease with which nucleophilic displacement of halogen from the 2- and 3-positions can be carried out. 

A few further examples of nucleophilic displacement of halogen from halogenothiophenes by a radical chain SrN, mechanism have been reported. The photostimulated reaction of 2-halo or 3-halothiophene with excess of tetrabutylammonium benzenethiolate in MeCN takes place by an SrN mechanism <87JOC5382>. The 2- or 3-(phenylthio)thiophene is formed in modest yields. The initiation and propagation steps are shown in Scheme 119. The first step may be the photostimulated electron transfer from thiolate anion to the halothiophene (ThX). The reaction does not take place in the dark. 

The two most general means of synthesis of organosilanes are nucleophilic displacement of halogen from a halosilane by an organometallic reagent and addition of silanes at double or triple bonds (hydrosilation). Organomagnesium and organolithium compounds... 

The mechanism of these reactions probably usually involves direct nucleophilic attack on the carbon system of the coordinated triene, although initial attack on coordinated carbon monoxide or on the metal, followed by rearrangement, may occur in some cases. Nucleophilic displacement of halogen from aryl halides is facilitated by coordination of the ring to the tricarbonyl-chromium group [Eq. (52)], but the reaction mechanism is more complicated than simple nucleophilic attack at the carbon carrying the chlorine atom, followed by elimination of chloride ion. Attack takes place at both ortho and meta positions in the aryl ring (Semmelhack and Hall, 1974) [Eq. (48)]. 

Other a-Functional Sulphones.—Nucleophilic displacement of halogen from a-halogenosulphones has long been known to be a sluggish reaction, but... 

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