ChemInform Abstract: AMINOPYRAZOLES. II. SYNTHESIS OF PYRAZOLO(3,4,‐B)PYRIDINES VIA VILSMEIER‐HAACK REACTION OF 5‐ACETAMINOPYRAZOLES

Abstract

Vilsmeier‐Haack‐Reaktion der Acetylamino‐ pyrazole (I) bei 90‐95°C liefert die Pyrazolopyridine (II) und (III), deren Strukturen durch unabhängige Synthesen von (IIb) und (IIIb) bestätigt werden.

Synthesis of benzo[3,4‐h][1,6]naphthyridines via Friedländer condensation with active methylenes

“…From literature, it was noted that o‐aminobenzaldehyde, the first and best known member of this class of compounds has been utilized for synthesis of various heterocycles [1–17]. Annulation reaction of heterocyclic aminoaldehydes provide a synthetic entry into heterocyclic systems fused to pyridine [18–21], pyrazole [22–25], and quinoline nucleus [26, 27]. The functionalized quinolines and their benzo/hetero‐fused analogous present in numerous natural products along with the wide spectrum of physiological activities [28].…”

Synthesis of 6-aryl-1,6-dihydro-dipyrazolo[3,4-b:4,3-c]pyridines

“…6-Chloro-3-methyl-1-phenyl-1H-pyrazolo[3,4-b]pyridine-5-carbaldehyde (1), synthesized from 5-acetylamino-3-methyl-1-phenylpyrazole by the Vilsmeier-Haack method [12] was proposed as the starting material for the synthesis of the desired materials. Compound 1, like 5-chloropyrazole-4-carbaldehyde [13][14][15], was converted in 85% yield to 6-azidopyrazolo[3,4-b]pyridine-5-carbaldehyde 2 by reaction with NaN 3 in DMSO in the presence of the phase transfer catalyst Bu 4 N + I -.…”

“…Only 1,7-disubstituted dipyrazolo [3,4-b:4,3-e]-pyridines can be synthesized by the reported cyclization of 2,6-dichloro-3,5-diformylpyridine with hydrazines [6], 5-aminopyrazoles with carbonyl compounds [7][8][9][10], and pyrazolin-5-ones with aldehydes and arylimines [11]. The intramolecular cyclocondensation of the hydrazone of 6-chloropyrazolo [3,4-b]pyridine-5-carbaldehyde was used to prepare 3-methyl-1-phenyl-1,7-dihydrodipyrazolo[3,4-b:4,3-e]pyridine [12]. There are no reports of 1,6-dihydro analogs of these heterocyclic systems in the literature.…”

Synthesis of 6-aryl-1,6-dihydrodipyrazolo[3,4-b:4,3-c]pyridines

“…The intramolecular cyclocondensation of the hydrazone of 6-chloropyrazolo[3,4-b]pyridine-5-carbaldehyde was used to prepare 3-methyl-1-phenyl-1,7-dihydrodipyrazolo[3,4-b:4,3-e]pyridine [12]. It is for this reason that we examine preparatively suitable routes to their synthesis in this paper.6-Chloro-3-methyl-1-phenyl-1H-pyrazolo[3,4-b]pyridine-5-carbaldehyde (1), synthesized from 5-acetylamino-3-methyl-1-phenylpyrazole by the Vilsmeier-Haack method [12] was proposed as the starting material for the synthesis of the desired materials. It is for this reason that we examine preparatively suitable routes to their synthesis in this paper.…”

“…Only 1,7-disubstituted dipyrazolo [3,4-b:4,3-e]pyridines can be synthesized by the reported cyclization of 2,6-dichloro-3,5-diformylpyridine with hydrazines [6], 5-aminopyrazoles with carbonyl compounds [7][8][9][10], and pyrazolin-5-ones with aldehydes and arylimines [11]. The intramolecular cyclocondensation of the hydrazone of 6-chloropyrazolo [3,4-b]pyridine-5-carbaldehyde was used to prepare 3-methyl-1-phenyl-1,7-dihydrodipyrazolo[3,4-b:4,3-e]pyridine [12]. There are no reports of 1,6-dihydro analogs of these heterocyclic systems in the literature.…”