Synthesis of Indazole‐N‐oxides via the 1,7‐Electrocyclization of Azomethine Ylides.

Abstract

Pyrazole derivatives R 0180Synthesis of Indazole-N-oxides via the 1,7-Electrocyclization of Azomethine Ylides. -Several indazole-N-oxides are obtained via intermediate 1,2,6-benzoxadiazepines, formed by 1,7-electrocyclization of azomethine ylides onto a nitro group. -(NYERGES*, M.; VIRANYI, A.; ZHANG, W.; GROUNDWATER, P. W.; BLASKO, G.; TOEKE, L.; Tetrahedron 60 (2004) 44, 9937-9944; Dep. Org. Chem. Technol., Tech. Univ. Budapest, H-1521 Budapest, Hung.; Eng.) -Klein 06-123

1,3-Dipolar Cycloaddition Reactions of Azomethine Ylides with Carbonyl Dipolarophiles Yielding Oxazolidine Derivatives

“…Subsequent ring-contraction afforded mixtures of indazole-N-oxides 100 and 3-methyl-5-aryloxazolidines 82b-e. It was postulated that the oxazolidine products were derived from the paraformaldehyde (2m) eliminated during this process, that reacted with excess sarcosine (47) to generate azomethine ylide 81, which underwent cycloaddition to another molecule of a 2-nitrobenzaldehyde derivative 2 (Scheme 23, Table 14) [94,95]. Azomethine ylides generated from sarcosine (47) and Ni(II) β-formyl-meso-tetraphenyl-porphyrins 101 underwent regioselective cycloaddition reactions with isatin (3b) to furnish the corresponding spiroporphyrin derivatives 102 in modest yields (Scheme 24) [96].…”

Silica Supported Polyphosphoric Acid Catalyzed Synthesis of Substituted Indazoles

“…15 Melting points were determined in open capillaries and reported uncorrected. 1 H NMR and 13 C NMR spectra were recorded on at 400 MHz instruments in CDCl3 using TMS as an internal standard.…”

“…10 Indazole N-oxide are also reported through 1,7-electrocyclization of azomethine ylides. 11 Condensation of o-fluorobenzaldehydes and their oximes with hydrazine 12 also yield indazoles, literature survey reveals that cyclization of o-substituted aryl hydrazones with halogens, nitro and methoxy 13 group as a substituent, 3substituted indazole and benzoisoxazoles synthesis via palladium catalyzed cyclization reactions. 14 Hangirgekar reported the synthesis of indazoles from 2alkoxy-acetophenone, hydrazine hydrate and a catalytic amount of Montmorillonite K-10 in different solvents ethanol, methanol, toluene, acetonitrile, DMF, THF and DMSO.…”