关键词: 扩环反应, 键活性, 吡喃盐, 三苯基环戊二烯

Abstract: A novel silver(Ⅰ) promoted carbon-carbon cleavage reaction of unstrained cyclopentadinene-ring, forming pyrylium cation, was reported previously. In order to explore the formation mechanism of pyrylium ring, in our continuous studies we investigated in detail the role of solvent, silver(Ⅰ) ions, water and molar ratio of silver(Ⅰ) salts to substrate in the reaction, and the effect of reaction temperature on the reaction rate. It was viewed that solvents with a high polarity can accelerate this reaction, and if toluene alone was used as solvent, the reaction could not commence. Silver(Ⅰ) ions in this reaction not only acted as the oxidants, but also as the catalyst considering the structures of substrate and pyrylium product. Trace amount of water existed in the solvents or absorbed on the substrate was crucial to this reaction, and the oxygen atom of the pyrylium ring was from water. Under 1∶2 molar ratio of silver(Ⅰ) to substrate, the reaction proceeded perfectly, whereas higher ratio led to a formation of multi-component products. Higher temperatures than ambient temperature would also complicate the products of reaction.

Key words: Ring-enlargement reaction, Bond activity, Pyrylium salts, Triphenylcycylopentadiene