Claisen rearrangements Bellus

Gonda, J. The Bellus-Claisen rearrangement. Angew. Chem., Int. Ed. Engl. 2004, 43, 3516-3524. 

Conceptually, this rearrangement is related to the Bellus-Claisen Rearrangement, in terms of ring expansion. This reaction is also related to the regular Claisen Rearrangement and Cope Rearrangement. 

Although this reaction is still at an early stage of development, a few modifications have been exploited. These modifications include the extension of the Bellus-Claisen rearrangement to ring strain molecules (such as 2-vinyloxetane, 2-vinyloxirane, and 2-vinylaziridines ) and to tertiary allyl amines, the application of chiral Lewis acid derived from Mgl2 and bis(oxazolinyl)aryl ligands, and the implementation of electron-rich ketene equivalents (e.g., alkoxyketenes, aminoketenes) by the photolysis of chromium carbene complexes. 

Other references related to the BelluS-Claisen rearrangement are cited in the literature. ... 

MacMillan has developed a Lewis acid-catalyzed Bellus-Claisen rearrangement in which a range of allylamines can add to ketenes via Lewis acids activation (253). This activation-addition pathway generates the zwitterionic allyl alkenyl ammonium complex as shovra for 250 which effectively rearranges to amide 251 with excellent syn selectivity. 

Application of this process in a tandem sequence was also reported by the MacMillan group. The -amine of diamine 254 preferentially reacted with the ketene to generate 258 which rearranged to allyl amine 259 with high syn selectivity. An additional equivalent of ketene triggered the second Bellus-Claisen rearrangement. This reaction proceeded via chair-like... 

Although examples of auxiliary-controlled stereoselective BelluS-Claisen rearrangements have appeared in the literature, the Lewis acid-mediated enantioselective version is a more attractive alternative for practitioners. MacMillan and Yoon have reported that the nonracemic Lewis acid complex 262 efficiently promotes an enantioselective Bellu -Claisen rearrangement with formation of amide 263 in good yield and with excellent selectivity. ... 

The ketene-Claisen rearrangement of a 1,3-dipolar allyl vinyl ether 124 is known as the Bellus-Claisen rearrangement [86]. 

A computational study of ring size effect on the Bellus-Claisen rearrangement shows the reaction to have a high asynchronous character (Scheme 13)7 ... 

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