Oxygen silver-catalyzed synthesis

Silver-Catalyzed Synthesis of Oxygen- or Phosphorus-Containing Heterocycles... 

As a part of a program directed toward the synthesis of the potent topisomerase I inhibitors, the lamellarins (e.g., 153 and 154), Porco has reported the silver triflate-catalyzed tandem cycloisomerization-azomethine ylide cycloaddition of 155 (Scheme 2.42).75 The postulated mechanism of this intriguing and highly efficient process is shown in Scheme 2.43. Silver-catalyzed addition of the imine nitrogen to the alkyne results, on subsequent deprotonation, in the formation of an azomethine ylide 160. This ylide participates in [3+2] cycloaddition with the alkyne component leading to formation of a dehydropyrrole 161. Finally, oxidation by adventitious oxygen leads to formation of the product 162. 

In woric related to natural product synthesis the efficacy of silver carbonate on Celite was compared with a platinum-catalyzed oxidation using an oxygen atmosphere for the oxidation of (23 equation 26). In some cases the Pt/Oz system was superior, but in others the situation was reversed, with no obvious rationale. The Pt/02 reagent has been used in the total synthesis of the hydroazulene natural products damsin (24 Scheme 7), aromatin (25) and aromaticin (26 Scheme 8). ... 

In work related to natural product synthesis the efficacy of silver carbonate on Celite was compared with a platinum-catalyzed oxidation using an oxygen atmosphere for the oxidation of (23 26). ... 

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