Nitrogen bridges

The exclusion of nitrogen-bridged bicyclic azines is purely arbitrary since the work on such azinoazines with a 10 7r-electron system (and the necessarily accompanying quaternary nitrogen-bridgehead atom) shows the activation expected of other aromatic azinium... 

Cyclazines may be considered as nitrogen-bridged annulenes rather than as hetarenes and, therefore, are only briefly mentioned in this volume. The chemistry of [3.3.3]cyclazines 1 and aza analogs, e. g. 3, is covered comprehensively in Houben-Weyl, Vol. E7b, p 205 IT. For another recent review, see ref 1. Subsequently, the chemistry of individual types of cyclazines has been reviewed, in particular 2.2.x]cyclazines,1 2 [2.2.2]cyclazines,3 [2.3.x]cyclazines4 and [2.2.3]-cyclazines.5 Moreover, the synthesis and the reactions of [2.2.3]cyclazines and the question of the effect of bcnzannulation have been addressed specifically.6... 

The transition states proposed for these exchange systems involve anion bridges For the system CrNCS -Cr, Ball and King suggest that either a nitrogen bridged transition state or a two stage process... 

Reaction of trietylenetetraamine (trien) with H [AuCU] at low pH leads to the water soluble dinuclear complex [Au2(trien-H)Cl3]Cl2, which features a deprotonated amino nitrogen bridging the two gold centers (Figure 2.10) [69]. 

Thus, Diels-Alder condensation of 9 with methyl vinyl ketone affords the bicyclic adduct 24. The new ring is formed by approach of the dienophile from the face containing the nitrogen bridge, since this is in fact the least hindered side of the molecule (9a). Reaction of the side Chain ketone with propylmagnesium bromide then leads to intermediate 25 demethylation of the... 

The significant difference is that in the final cyclization step from the bicyclo to the tricyclo system the oxygen bridge is formed in the former and the nitrogen bridge in the latter procedure. Thus, the first step in the former... 

The methodology is useful for a variety of synthetic purposes. The cycloadditions are not subject to steric hindrance. Thus diyne cycloadditions to 2,5-disubstituted furans or pyrroles, followed by elimination of the oxygen or nitrogen bridges, provides an excellent, short route to peri-substituted arenes, as in the following examples 4 6 8... 

Use has been made of the C-N cleavage in the conversion of the bicyclic tertiary amines, derived from the 4tc + 2tc cycloaddition of pyrroles and isoindoles with benzynes, into aromatic systems, e.g. naphthalen-l,4-imines and anthracen-9,10-imines yield naphthalenes and anthracenes with the extrusion of the nitrogen bridge [24] in yields which are higher than those obtained by standard oxidation procedures. 

Nonconjugated enones and ynones that contain a sulfur or nitrogen bridge could be regio- and diastereoselectively hy-drodimerized to cyclic alcohols [316]. 

Various analogues have been investigated indicating that the nitrogen-bridge between the two aromatic rings is the target, at least for HOCl oxidation. When alter-... 

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