Nucleophilic Aromatic Substitution

Abstract

There has been a study of the dediazoniation of 4-nitrobenzenediazonium ions in methanol-water mixtures under acidic conditions using kinetic, spectrophotometric, and chromatographic methods. Two decomposition routes were identified: an ionic pathway yielding nitrophenol and nitroanisole, and a radical pathway involving transient diazo ethers which undergo homolytic fragmentation giving nitrobenzene or 4,4 -dinitrobiphenyl. 1 Catalysis by the Cu(I)-Cu(II)-1,10-phenanthroline system has been reported in the reaction of arenediazonium salts with potassium thiocyanate to yield aryl thiocyanates. 2 Bis(trifluoromethanesulfonyl)amide anions (Tf 2 N − ) are usually considered to have very low nucleophilic reactivity. However, in imidazolium ionic liquids this anion has been shown to have higher reactivity than bromide ions in heterolytic dediazoniation reactions. 3 It has been shown that displacement of the iodo substituent in 4-iodo-1,1,2,2,9,9,10, 10-octafluoro[2.2]paracyclophane by arenethiolates or by stabilized enolates occurs by the radical chain S RN 1 mechanism. The reaction occurs in DMF with photochemical stimulation. 4 The S N Ar MechanismThere has been a review of relationships between activation parameters and mechanisms for biomolecular reactions in solution, including both nucleophilic substitutions and additions. 5 Several studies have been reported involving substitutions by amine nucleophiles where both electronic and steric effects may be important. Kinetic studies of the reactions of 2,4-dinitrophenyl 2,4,6-trinitrophenyl ether (1) with ring-substituted 175

Access and Regioselective Transformations of 6-Substituted 4-Aryl-2,8-dichloropyrido[3,2-d]pyrimidine Compounds

“…The synthesis of such a scaffold 1 , with different groups at C-6, provided an interesting challenge. Only two examples were reported. , Then regiocontrolled diversification of the resulting scaffold 1 is described through S N Ar and metal-catalyzed cross-coupling reactions, starting with a C-4 arylation, and leading to a set of novel and diverse C–N- and C–C-substituted pyrido­[3,2- d ]­pyrimidines 9 , 10 , 15 , and 16 (Scheme ).…”