Accessing Multiple Classes of 2H-Indazoles: Mechanistic Implications for the Cadogan and Davis–Beirut Reactions

Abstract

The Cadogan cyclization is a robust but harsh method for the synthesis of 2H-indazoles, a valuable class of nitrogen heterocycles. Although nitrene generation by exhaustive deoxygenation is widely accepted as the operating mechanism in the reductive cyclization of nitroaromatics, non-nitrene pathways have only been theorized previously. Here, 2H-indazole N-oxides were synthesized through an interrupted Cadogan/Davis-Beirut reaction and are presented as direct evidence of competent oxygenated intermediates; mechanistic implications for both reactions are discussed. Isolation and characterization of these N-oxides enabled a formal Cadogan cyclization at room temperature for 2H-indazole synthesis.

Addition reactions of a phosphorus triamide to nitrosoarenes and acylpyridines

“…C-H hydrogen atoms excluded for clarity. Selected bond lengths (Å) and angles (°) of P-O(1) 1.47(0), P(1)-N(1) 1.67 2, P(1)-N(2) 1.68 3 On the basis of prior literature which supports the formation of nitrene or nitrenoid reactive intermediates by deoxygenation of nitro-and nitrosoarenes, [26,[38][39][40] deoxygenation is extensively supported in the literature. [2,23,24,[42][43][44]…”

Towards Knowledge Maintenance in Scientific Digital Libraries with the Keystone Framework

“…Three of the articles [1,50,51] cited the WH protocol in order to support a linear regression fitting between the theoretical and experimental NMR shifts. They are pass-through keystone citations, because the support is provided not directly by the WH protocol but rather by its bibliography (WH protocol's Ref 19).…”

Intermediate formation enabled regioselective access to amide in the Pd-catalyzed reductive aminocarbonylation of olefin with nitroarene

“…Nitroarenes are generally cheaper, more readily available, and more functionally compatible than anilines as nitrogen sources [1][2][3][4]. Therefore, using nitroarenes as starting molecules is advantageous for preparing nitrogen-containing functional molecules in proper cascade reactions [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19].…”