Facile Syntheses of Novel Benzo- 1,3-dioxolo-, Benzothiazolo-, Pyrido-, and Quinolino-fused 5H-Benzo[d]-pyrazolo[5,1-b][1,3]-oxazines and 1H-Pyrazoles

Abstract

A number of novel benzo-1,3-dioxolo-, benzothiazolo-, pyrido-, and quinolino-fused 5H-benzo[d]pyrazolo[5,1-b][1,3]-oxazines and 1H-pyrazoles were synthesized utilizing an easy and effective N,N-bond forming heterocyclization reaction. In so doing, the substrate scope of this heterocyclization reaction, which starts with o-nitroheterocyclic aldehydes, was expanded to provide several unique heterocyclic compounds for biological screening. This work further demonstrates the versatility of this simple, base-mediated, one-pot heterocyclization method in the construction of novel heterocycles.

Acid and base catalyzed Davis–Beirut reaction: experimental and theoretical mechanistic studies and synthesis of novel 3-amino-2H-indazoles

“…4b,c As depicted in Scheme 2, we propose that o -nitrobenzylamine 7 delivers hemiaminal nitroso intermediate 8 under basic conditions and subsequent loss of water renders o -nitrosobenzylidine imine 9 . This o -nitrosobenzylidine imine is an important intermediate that engages two possible pathways to the 2 H -indazole product.…”

“…3 In recent years, we have reported the syntheses of a number of pyrazolo-based heterocycles ( 1 ), 2 H -indazoles ( 2 ) and, subsequently, 1 H -indazolones ( 3a/b ) that were obtained via the Davis-Beirut reaction (Figure 1). 4 We previously suggested that o -nitrosobenzylidine was an important intermediate in this chemistry. As part of our ongoing interest in the development of the Davis-Beirut reaction, we report here both acid and base-catalyzed examples that provide mechanistic insight into the reactions shown in Scheme 1.…”

Chemoselective and diastereoselective synthesis of halogenated [1,3] oxazino [2,3‐a] isoquinoline derivatives

“…The chemistry of [1,3] oxazines has long kept a special place among N , O ‐heterocycles . Subunits of those, fused [1,3] oxazines with a bridgehead nitrogen atom and susceptible to biological and medicinal properties, are of interest to chemists .…”

Propargyl Hydrazides as Useful Intermediates Leading to Pyrazoles via Reaction with Certain Electrophiles

“…Recently, we reported the regioselective synthesis of pyrazoles from propargyl alcohols with tosylhydrazine via the corresponding hydrazides, which were isolated by our original procedure . Hydrazones have been reported to be a good tool for the synthesis of pyrazoles via intra and intermolecular cyclization reactions with alkynes,, cyclobutanones, and other substituted pyrazoles . However, the corresponding hydrazides are much more rare than the corresponding hydrazones , .…”