84499-24-1Relevant articles and documents
Base-Catalyzed Rearrangement of N-(Aryloxy)pyridinium Salts. Effect of a 3-Substituent in the Pyridine Ring upon Orientation. Synthesis of Novel Tricyclic Rings
Abramovitch, Rudolph A.,Inbasekaran, Muthiah N.,Kato, Shozo,Radzikowska, Teresa A.,Tomasik, Piotr
, p. 690 - 695 (2007/10/02)
The orientation in the base-catalyzed rearrangement of 3-substituted N-(aryloxy)pyridinium tetrafluoroborates (5) to 2- or 6-(2-hydroxyaryl)pyridines has been studied.A 3-methyl group directs exclusively to the 6-position while inductively electron-withdrawing substituents (Cl, Br, I, OMe, CO2Me, COMe) direct mainly, if not exclusively, to C-2.The phenols derived from 3-CO2Me derivates cyclize spontaneously to the substituted pyridocoumarins (8) in useful yields, and that from the 3-COMe compound gives 10-hydroxy-10-methyl-6-nitropyridobenzopyran (9).The 3-halo-2-(2-hydroxyaryl)pyridines cyclize to benzofuropyridines(10,15) on heating with potassium hydroxide and copper powder.Authentic benzofuropyridine (12) is obtained by the Pschorr ring closure of the diazonium salt of 3-(o-aminophenoxy)pyridine (14).The substituent effects are explained mainly on the basis of the inductive effect of the substituent: steric effects play a slight role.A minor side reaction is thought to involve the intermediacy of free radicals.
