Favorskii rearrangement Lewis acids

All of the examples described thus far have involved the use of bases to initiate the Favorskii rearrangements. However various Lewis acids have also been used for this purpose. An early example of this methodology is shown in Scheme A2P The Lewis acid promoted ring contractions depicted in Scheme 43 and Scheme 44 are also Favorskii-type rearrangements. 

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