Systems with Bridgehead Nitrogen

The cryptands are generally characterized by three heteroatom-containing strands which meet at a common point to which we have generally referred as bridgehead . For most of the compounds which have been reported, this bridgehead is a nitrogen atom and conformational flexibility is attributed to inversion at this atom. In this section we consider other bridgehead units, specifically those in which carbon is the bridgehead atom. In fact in these cases, the flexibility associated with nitrogen inversion is absent and it is the flexibility of the entire group which permits whatever conformational mobility there is.  [c.352]

The reactions of 12.29 have not been investigated extensively. Treatment of aryl derivatives with chlorine gas produces S,S -dichlorodithiatriazines, 12.9, whereas the CF3 derivative is unaffected by Cla. Nucleophilic attack by EPh3 (E = P, As) transforms the bicyclic compound 12.29 (R = Ph) into the monocyclic eight-membered ring 12.30 (Eq. 12.8). The trifluoromethyl derivative 12.29 (R = CE3) behaves as an A-monodentate ligand towards Ni or Ag" via the bridgehead nitrogen atom an A,A -bridging mode is also observed in the Ag" complex. Consistently, calculations confirm that the largest negative charge resides on the bridgehead nitrogen atom. Protonation, on the other hand, occurs at a nitrogen atom linked to the carbon centre. Interestingly, the Hg " cation converts 12.29 (R = CP3, NMea, Ph) to the corresponding planar, eight-membered rings 12.27 (Section 12.4.2). "  [c.254]

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  [c.148]

Advances in heterocyclic chemistry Vol.85 (2003) -- [ c.0 ]