Über Bildung von Indazolkörpern aus orthomethylierten Anilinbasen

Abstract

Pehlten clagegen solctie begunstigenden Subditueiiteu, 30 $5 ar Iwim Verkochen der Uial;oniumsalze keine Indazolbildung zu bemerken'). Doch gelang es clurch andersartige Behandlung. auch in solc h r n Phllen die Diazokorper znm IndazolrinqschluIj zn veranlassen. Barn b e r g e r ' ) zeigte, da13 orthoni~thylierte Diazoniumsalze nnter der Einnirkung von N a t r o n l a u g e je zwei IndazolkBrperclas einhclie Indazol (I) und sein Brv1:izoderivat (11) -liefern. N h l t i n g 3, fand, d:ifi rliazotiertes o-'l'oluidin bei der Zersetzung in n e n t r a l e r LBsung zitin Teil sich in Iudazol univandelt. Bber die -4usbeuten an Indaz d selbst bzm. seinen Homologen sind bei diesen Prozessen so winzig. daM dieser Weg fur pelparati\ e Zwecke kaum in Retracht komnieii knnu.Durch einen Zufall haberi ~i r eine Iieaktionsfolge aufgefunden, die rinen r e c h t g l a t t e n U b e r g a n g d e r o r t h o m e t h y l i e r t e n , v o n n eg a t ive i i S u b s t i t n e LI t e ii f r e i e n A n i l i n b a s e n z u I n d a z o le n eitn6glicht. Sie beruht daranf, dal3 die N -X i t r o s o v e r b i n d u n g e i i d z I a c y 1 i e r t e n , o r t h o ni e t 11 y 1 i e r t e n , a r o m a t i s c h e n

An Efficient, Facile, and General Synthesis of 1H‐Indazoles by 1,3‐Dipolar Cycloaddition of Arynes with Diazomethane Derivatives

“…Because of this usefulness, considerable effort has been devoted to the development of efficient methods for the construction of indazole frameworks (Scheme ) 2. The common synthetic routes are diazotization of the corresponding 2‐alkyl anilines2a and nitrosation of the N ‐acetyl derivatives of 2‐alkyl anilines (Jacobson modification);2c–e another attractive route is the condensation of ortho ‐substituted benzaldehydes with hydrazine 2f,g. However, the reaction conditions of these methods are fairly harsh: Usually strong acids or high temperatures are required.…”

Base‐Catalyzed Synthesis of Substituted Indazoles under Mild, Transition‐Metal‐Free Conditions

“…Although several procedures for the preparation of indazole derivatives are known,6 the discovery of new methods that are milder than the classical routes, such as the diazotization or nitrosation of anilines and the condensation of benzaldehydes with hydrazines, is desirable. Those methods often require an excess of a highly toxic or unstable hydrazine,6d,i,l hydrazone,6b,f nitro,6e or diazo6a,c,j compound, and the reaction conditions tend to be harsh and involve strong acids or high temperatures.…”

Base‐Catalyzed Synthesis of Substituted Indazoles under Mild, Transition‐Metal‐Free Conditions

“…Although several procedures for the preparation of indazole derivatives are known, [6] the discovery of new methods that are milder than the classical routes, such as the diazotization or nitrosation of anilines and the condensation of benzaldehydes with hydrazines, is desirable. Those methods often require an excess of a highly toxic or unstable hydrazine, [6d,i,l] hydrazone, [6b,f] nitro, [6e] or diazo [6a,c,j] compound, and the reaction conditions tend to be harsh and involve strong acids or high temperatures.…”