Homogeneous Oxidation Of Polysubstituted Cyclopentadienes With Transition-metal Salts

Pyrylium salts are a type of organic aromatic compounds with one or more six-numbered oxoheterocyclic cations, which are practically valuable owing to their peculiar chemical and physical properties. They are of great chemical reactivity and can used as synthetic intermediates for a large number of organic compounds. They are of good optoelectric porperities, investigations on which in recent years have become a hot topic. For example, they can used as photosensitizers to catalyze photodegradation of organic compounds in wastewater, as laser dyes, labbelling molcues foe proteins, and as organic electrolyte.The present synthetic methods for pyrylium salts mainly include 1,5-dione and yneone methods. Both of the two methods include combination of short-chain molecules (usually within three carbons in chain) into chain-like intermediaes including five carbons and one (or two) oxygen atoms in chain, cycloisomerization of the intermediate, and (or) oxidation processes to obtain pyrylium products. One of limitations of the two methods is that the pyrylium-fromation process usually requires tedious procedures and severe reaction conditions. In contrast, there has been no report on the synthesis of pyrylium salts by oxidation and ring-enlargement reactions of substituted cyclopentadienes promoted by some soluble transition metal ions. Using cyclic cyclopentadienes as starting materials, the advantages of this method are: It is an one-pot method, which is easily manipulating, and requires mild conditions; It can synthesize not only α,α'-disubsituted pyrylium salts, but also α-monosubsituted pyrylium salts, which are chemically active and are difficult to synthesize by the present methods. The theme of this dissertation is to study systematically the new reaction on cyclopentadienes. The results are listed below:1. A series of cyclopentadiene derivatives, including 1,2,4-triphenylcyclopentadiene, 1,2,3,4-tetraphenylcyclopentadiene, 1,2,3,4,5-pentaphenylcyclopentadiene, 5-methyl- 1,2,3,4-tetraphenylcyclopentadiene, 5-ethyl-1,2,3,4-tetraphenylcyclopentadiene, 2,3,4,5-tetraphenyl-cyclpentadiene-1-ol, tetracyclone, and 5-bromo-1,2,3,4-tetraphenylcyclopentadiene, are synthesized, and some synthetic steps are improved and simplified.2. The universality of the oxidation and ring-enlargement reaction on cyclopentadiene derivatives, and the relationship between the structure of cyclopentadiene derivatives and the structure of pyrylium cations, are discussed based on the study the reactions of a series of cyclopentadiene derivatives with silver perchlorate in benzene/dichloromethane solvent. It is found that, oxidation and ring-enlargement reactions can be carried out when cyclopentadienes can be existed stablely as monomer at room temperature, and are nonsubstituted, or monoalkyl or mono aryl substituted on C_sp3 in cyclopentadiene rings,. In contrast, benzocyclopentadienes, and cyclopentadienes which are easly dimerized at room...