ChemInform Abstract: Unprecedented Rearrangement of 2‐(2‐Aminoethyl)‐1‐aryl‐3,4‐dihydropyrazino[1,2‐b]indazole‐2‐ium 6‐Oxides to 2,3‐Dihydro‐1H‐imidazo[1,2‐b]indazoles.

Base-Mediated Intramolecular C- and N-Arylation of N,N-Disubstituted 2-Nitrobenzenesulfonamides: Advanced Intermediates for the Synthesis of Diverse Nitrogenous Heterocycles

“…The key structural element is the acidic proton on the α-carbon. In our previous work, we studied the C-arylation (and subsequent nitrogenous heterocycle formation) of substrates 1 with R 2 = CH 2 -CO-Ar or CH 2 -COOMe and R 3 = H. − Our recent results indicated that N -benzyl derivatives 1 with R 2 = Ar and R 3 = H can also be arylated at the sp 3 carbon when strong electron-withdrawing groups are present on the aromatic ring (2- or 4-NO 2 , 4-CF 3 , 4-COOMe, or 2- or 4-pyridyl derivatives)…”

“…We previously reported the solid-phase synthesis of 2 H -indazole 1-oxides (Scheme ) via tandem carbon–carbon bond formation followed by nitrogen–nitrogen bond formation. , The key transformation involved C-arylation triggered by a DBU-mediated Smiles-type rearrangement of 2-Nos amides. This very efficient (high yield and purity were obtained using commercially available building blocks) synthesis of indazoles prompted us to expand the chemical route and apply C-arylation to the synthesis of indazole-derived heterocycles, including pyrazino[1,2- b ]indazoles and 2-(2-amino/hydroxyethyl)-1-aryl-3,4-dihydropyrazino[1,2- b ]indazole-2-iums, which cyclized to fused tetracyclic heterocycles and rearranged to 2,3-dihydro-1 H -imidazo[1,2- b ]indazoles . Base-catalyzed ring expansion of 2 H -indazole 1-oxides prepared from Gly provided access to quinazolines .…”

Mining the Chemical Space: Application of 2/4-Nitrobenzenesulfonamides in Solid-Phase Synthesis

“…Depending on the reaction conditions, type of base, substitution pattern, and structure of the individual linkers, C-arylated intermediates 128 were converted into various indazole oxides and iminium salts suitable for other chemical transformations (Scheme ). ,,− …”

Solid-Phase Synthesis of Trisubstituted 2,5-Dihydrobenzo[f][1,2,5]thiadiazepine 1,1-Dioxide Derivatives

“…The principal modification is the use of the 2-nitrobenzenesulfonyl (2-Nos) group as a building block rather than as a protecting/activating group. We have already exploited the 2-Nos group in our previous syntheses of nitrogenous heterocycles. − …”