Breslow intermediates transformations mediated

A prominent example of this catalytic methodology is the Stetter reaction. Although numerous NHC-organocatalysed versions of this reaction have been developed, it is only very recently that a mechanistic investigation has been detailed in the literature. The intramolecular asymmetric Stetter reaction of substrates (102) catalysed by triazolinylidene-based NHC (103) has been employed as the model reaction and the experimental results obtained have evidenced that the [l,2]-proton shift giving precisely Breslow intermediate (101) is not only slow but above all, the first irreversible step of the transformation. Also noteworthy is that (102) precursors are prone to cyclize not only to the expected six-membered Stetter products (104) but also to benzofurans (105), the latter resulting from a base-mediated mechanism related to the basic feature of the catalyst. 

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