Aza-Claisen and Related Rearrangements

The aza-[2,3]-Wittig rearrangement [47] and the related aza-[3,3]-Claisen rearrangement [48] of vinylaziridines are elegant examples of expansion of the aziridine ring in a stereocontrolled fashion (Scheme 38). 

In 1997 the first asymmetric aza-Claisen rearrangement was reported by Overman et al. [55], which made use of diamines as bidentate ligands for Pd(II), allowing for moderate enantioselectivities. In the same year, Hollis and Overman described the application of the planar chiral ferrocenyl palladacycle 38 as a catalyst for the enantioselective aza-Claisen rearrangement of benzimidates 39 (Fig. 19) [56]. A related ferrocenyl imine palladacycle provided slightly inferior results, while a benzylamine palladacycle lacking the element of planar chirality was not able to provide any enantioselectivity [57]. 

This reaction is closely related to the Aza-Claisen Rearrangement, Claisen Rearrangement, and Abnormal Claisen Rearrangement. 

The nitrogen analog of the simple Claisen rearrangement with N-allylaniUne and related derivatives is called the amino-Claisen rearrangement (or aza-Claisen rearrangement) [55]. Under thermal conditions, more drastic conditions (310-340 °C) compared with that for the oxygen substrates is required to obtain the ortho allyl aniline 59 [56]. N-Allyl aniline derivatives are, however, not stable at such... 

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