Claisen rearrangement zwitterionic

C4-insertions by means of a sigmatropic rearrangement process have been described using either a thermal Cope reaction, anionic Claisen amide enolate and zwitterionic aza-Claisen rearrangements. 

An alternative pathway using a zwitterionic aza-Claisen rearrangement to generate azoninones has been described by Hegedus [61]. 2-Vinylpyrrolidines... 

An approach in constructing the basic reserpine skeleton via the amino Claisen rearrangement of zwitterionic vinylisoquinuclidenes has been investigated (256, 257). 

Fig. 2 Systems suitable for the intermolecular zwitterionic aza-Claisen rearrangement...

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. 

U. Nubbemeyer et al. achieved the enantioselective total synthesis of the bicyclic tetrahydrofuran natural product (+)-dihydrocanadensolide via a key step utilizing the diastereoseiective zwitterionic aza-Claisen rearrangement of an N-allylpyrrolidine. ... 

Zwitterionic [3,3]-sigmatropic rearrangements. The zwitterionic aza-Claisen rearrangement is useful for ring expansion. It is subject to 1,2-asymmetric induction. ... 

Examples of the aza-Claisen rearrangement of allyl vinyl amines and the thia-Claisen rearrangement of allyl vinyl sulfides have been reported. An efficient Lewis acid-catalysed Claisen rearrangement of zwitterionic A-acyl allylic amines... 

More recently, several variations of the Claisen rearrangement have been reported that also possess some of the features of the Ireland variant, including the amide Claisen, S,S- and N,S-ketene acetal Claisen and the zwitterionic Qaisen rearrangements [2]. This review will focus on the Ireland variant of the Qaisen rearrangement in which a sUyl ketene acetal is an intermediate, although mention will be made of boron ketene acetals where appropriate. 

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