63801-86-5Relevant academic research and scientific papers
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.
Aryloxenium Ions. Generation from N-(Aryloxy)pyridinium Tetrafluoroborates and Reaction with Anisole and Benzonitrile
Abramovitch, Rudolph A.,Alvernhe, Gerard,Bartnik, Romuald,Dassanayake, Nissanke L.,Inbasekaran, Mutiah N.,Kato, Shiego
, p. 4558 - 4565 (2007/10/02)
N-(Aryloxy)pyridinium tetrafluoroborates (4) decompose thermally at 180-200 deg C in anisole and benzonitrile to form products of intermolecular C-O-C and C-C bond formation.With anisole, diphenyl ethers (5) and hydroxybiphenyls (6) are formed; with benzonitrile, the main product is benzoxazole (14).A homolytic process was ruled out by showing that none of these products were formed when perbenzoyl p-nitrophenyl carbonate (18) was decomposed in these solvents.The main products in this case were those of homolytic phenylation (and benzoyloxylation with anisole).A concerted SN2-type heterolytic process was ruled out by showing that the nature of the substituent in the pyridine ring had no effect on the isomer ratios of 5 and 6 in the thermolysis of 4 (X = p-NO2) in anisole.The results are explained in terms of a unimolecular heterolysis of 4 to give the pyridine and aryloxenium ion 2 which now attacks solvent molecules.When an electron-withdrawing substituent is present in 2, more C-O-C than C-C products are formed in anisole.When it is absent only products of C-C bond formation are found.PhO+ is apparently electrophilic enough to attack anisole and give the four possible hydroxymethoxybiphenyls (10-13).
