Silver promoted cascade reaction

Scheme 7.42. Synthesis of a-hydroxy acids from a-ketoesters through a silver-promoted cascade reaction.

This chemistry has been revamped more recently by its combination with cyclization reactions, most of them also promoted by silver salts.69 More recent years have thus witnessed the development of silver-catalyzed cascade reactions leading to heterocycles under mild conditions.68... 

In more sophisticated approaches, [3,3]-sigmatropic rearrangements have been incorporated in cascade reactions in which each step could be catalyzed by silver salts. Usually, the silver promoted [3,3]-sigmatropic shift is combined with a silver-catalyzed cyclization,68 as outlined in the general scheme below for alkynyl compounds (Scheme 3.44). 

The cascade sequences presented herein demonstrate unprecedented modes of reactivity in Nazarov chemistry that are initiated by the silver(I)-promoted ring opening of halocyclopropanes. The ease with which the gem-dichlorocyclopropanes can be prepared, the relatively mild reaction conditions, and the efficiency of these processes make these substrates attractive intermediates for an application in natural product synthesis. 

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