1.3- Diaza-Claisen rearrangments

Bridged bicyclic tertiary allylic amines aza-norbornene and isoquinuclidene have been reported to add to isocyanates, isothiocyanates, and in s/tM-generated carbodiimides to form zwitterionic intermediates that undergo 1,3-diaza-Claisen rearrangements to ureas, thioureas, and guanidines, respectively (Scheme 26) ... 

Thus, ketenes (2) can react as dienophiles with (E)-l,3-diazabuta-l,3-dienes (E)-(25) to yield either [4 + 2] cycloaducts (26) or (27) depending on the participation of the C = C or C = O moieties of the ketenes (Scheme 7). Claisen rearrangement of 3,6-dihydro-2-methylene-2//-l,3,5-oxadiazines (27) yields the p-lactams (28). Alternatively, reaction between ketenes (2) and (Z)-l,3-diaza-buta-1,3-dienes (Z)-(25) leads to the usual zwitterionic intermediates (29), whose conrotatory electrocyclation leads to p-lactams (28). No computational data including solvent effects have been reported for these reactions. 

The N-analogs1 8 of the Cope and Claisen rearrangement have been widely used for syntheses of amines and /V-heterocyclcs, for example, the l,l -diaza-Cope rearrangement is the key step in the Fischer indole synthesis. 

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