Facile N-arylation of amines and sulfonamides.

Reaction of arynes, N-heteroaromatics and nitriles

A general method for Pd-catalyzed sulfonamidation of aryl nonafluorobutanesulfonates (aryl nonaflates) is described. A biaryl phosphine ligand, t-BuXPhos, formed the most active catalyst, and K3PO4 in tert-amyl alcohol was found to be the optimal base–solvent combination for the reaction. The reaction conditions were tolerant of various functional groups such as cyano, nitro, ester, aldehyde, ketone, chloride, carbamate, and phenol. Heterocyclic aryl nonaflates were found to be suitable coupling partners. High yields of the coupled products were obtained from the reactions between inherently disfavored substrates such as electron-rich nonaflates and electron-poor sulfonamides. Kinetic data suggest reductive elimination to be the rate-limiting step for the reaction. The only limitation of this methodology that we have identified is the inability of 2,6-disubstituted aryl nonaflates to efficiently participate in the reaction.

A general method for palladium-catalyzed reactions of primary sulfonamides with aryl nonaflates.

Facile synthesis of N-alkyl-N'-arylimidazolium salts via addition of imidazoles to arynes.

The reaction of benzynes with N-heteroaromatics including quinolines, isoquinolines, and pyridines and various terminal alkynes or ketones with an alpha-hydrogen in the presence of KF and 18-crown-6 in THF at room temperature for 8 h gave various N-arylated 1,2-dihydroheteroaromatics in good to moderate yields. Some of these product structures are found in various naturally occurring and biologically active heterocyclic compounds. The reaction involves an unusual multiple construction of new C--C, C--N, and C--H bonds and the cleavage of a C--H bond in one pot. It is likely that the three-component coupling proceeds through the nucleophilic addition of quinoline to benzyne, which generates a zwitterionic species. The latter then attracts a proton from terminal alkyne (or ketone) to generate an N-arylated quinolinium cation and an acetylide anion. Further reaction of these two ions provides the final substituted 1,2-dihydroquinolines. In the reaction, the terminal alkyne acts first as a proton donor and then as a nucleophile. The application of a three-component coupling reaction product, 1,2-dihydro-2-pyridinyl alkyne in a stereospecific [4+2] Diels-Alder cycloaddition reaction with N-phenyl maleimide to give an isoquinuclidine derivative, an important core present in various natural products, is demonstrated.

Synthesis of N-arylated 1,2-dihydroheteroaromatics through the three-component reaction of arynes with N-heteroaromatics and terminal alkynes or ketones.

Durch direkte Lichtanregung werden die drei 7-Aza-benzonorbornadiene 12a, b, c in die 3-Benzazepine 22a, b, c isomerisiert. Oberhalb −40° lassen sich die als Zwischenprodukte postulierten Azaquadricyclane 19a, b, c nicht nachweisen. Bei der sensibilisierten Anregung von 12a werden die 6-Amino-2.3-benzo-fulvene 23a, 24a bevorzugt gebildet.



Photochemical Transformations, 33



Upon direct photoexcitation the three 7-azabenzonorbornadienes 12a, b, c are isomerized to the 3-benzazepines 22a, b, c. At temperatures above −40° the azaquadricyclanes 19a, b, c, postulated as intermediates, cannot be found. The sensitized reaction of 12a yields the 6-aminobenzofulvenes 23a and 24a preferentially.

Horst Prinzbach

Papers

Photochemische Umwandlungen, 33. Photochemische Isomerisierung anellierter Aza‐norbornadiene