Effect Of Connecting Groups And Substituents On The Aromatic1,5-hydrogen Transfer In Pschorr Cyclization

Pschorr cyclization has been widely used in preparation of polycyclic compounds, especially in drugs and functional dyes, and it has been a key step in a number of carbocyclic and heterocyclic ring forming transformations. The yield usually is low and byproducts are many, because there are several competitive reactions of the aryl radicals generated in the reaction process. In recent years, aromatic radical-induced intramolecular aromatic1,5-hydrogen transfer was discovered via Pschorr cyclization but the study of the compound system is not many. Therefore, further study at the types of substrates, substituents and cyclization conditions and other factors which can effect Pschorr reaction and intramolecular1,5-hydrogen is very significant.Naphthalic anhydride and naphthalimide derivatives3a-3i underwent Pschorr cyclization which have been synthesized from1,8-naphthalic anhydride though Ullmann condensation, imidization and nitron reduction reaction. Pschorr products of3c-3i are detected which confirms that there are aromatic1,5-hydrogen transfer. Proportions of isomers range from13.2%to40.0%. Products were separated and purified. The target compounds may be obtained and were tested the spectroscopic properties.Different reaction conditions were studied on the influence on the reaction of compounds3e,3f,3h, including diazo reagent (concentrated sulfuric acid, fluoroborate), inducing reagent (copper sulfate, cuprous oxide, ferrous sulfate) and different reaction solution (acetic acid solution,1M sulfuric acid solution, water, saturated sodium bicarbonate solution). In the condition of concentrated sulfuric acid and acetic acid solution with copper sulfate reaction system, the LC-MS result shows the improvement of by-products and increase of aromatic1,5-hydrogen transfer products. The reaction system can be seen as the optimum condition.Under the optimal reaction conditions, phenyl naphthyl amine, ether and thioether substrates3c-3q were underwent Pschorr cyclization to analysize the effect of substituents and connecting groups on cyclization yield and the rate of aromatic1,5-hydrogen transfer. The results showed that, the yield of the amino-diazonium salt is very low, more by-products, and the rearrangement product ratio is strongly influenced by the substituent; the yield of oxa-diazonium salt cyclization is moderate, rearrangement product ratio is influenced by the substituent; the thio-diazonium salt cyclization product yield is very high, rearrangement product is very low, which less affected by the substituents. When the electrondonating ability of the groups connected to the naphthalene ring enhances, the ratio of the rearrangement product rises.