Silver catalysts natural product synthesis

The central six-membered ring unit in the illudalane or pterosin class of sesquiterpenes makes them a suitable target for a proof of the synthetic power of the transition-metal-catalyzed [2 + 2 + 2] alkyne cycloaddition in natural product synthesis. A first example in this field was provided by the intramolecular version of the [2 + 2 + 2] alkyne cyclotrimerization in the synthesis of calomelanolactone (15) [8] and pterosin Z (16), both of which have been isolated Ifom the silver fern Pityrogramma calome-lanos (Scheme 7.4) [9]. Wilkinson s complex served here as the catalyst, and the cyclotrimerization of triyne 13 proceeded at room temperature to give the tricycle 14. The latter was used as a common synthetic intermediate for completion of the synthesis of calomelanolactone (15) and pterosin Z (16) within four and three synthetic steps, respectively. 

Several silver complexes have been investigated in C-H insertion reactions of carbenes. One of the earliest reports by Sulikowski and Burgess describes an intramolecular C-H insertion of a chiral aryl diazoacetate 80 as part of a study on the total synthesis of mitomycin family of natural products (Scheme 8.15).41 Among several catalysts that were screened was AgSbly, in the presence of bis(isoxazoline)-type ligands, which led to the formation of the desired insertion product 81 in moderate yield and modest diastereoselectivity. 

The aldol reaction is one of the most useful and classical reactions in organic synthesis, since the resulting p-hydroxycarbonyl compounds are highly useful building blocks for pharmaceuticals and natural products.14 The asymmetric version of this reaction has been developed to a significant extent. We focus here on the asymmetric classical aldol reaction using a silver catalyst and related reactions.15... 

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