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2005
Fused pyridine derivatives
R 0450
A Versatile Synthesis of Pyrazolo[3,4-c]isoquinoline Derivatives by Reaction of
with Aryl/Heteroaryl Aldehydes: The Effect of the
31- 142 4-Aryl-5-aminopyrazoles
Heterocycle on the Reaction Pathways. — The reaction of 4-aryl-5-aminopyrazoles
(I) with aromatic aldehydes like (IIa)—(IIc) in strong acidic media proceeds with initial
azomethine formation, followed by a Pictet—Spengler-like condensation and dehydrogenation to give title pyrazolo[3,4-c]isoquinolines (III) in good yields. The reaction
with heterocyclic aldehydes, however, can follow different pathways depending on the
heterocycle. Thus, analogous cyclization is achieved with 3-pyridyl-, 3-quinolinyl-,
3-thienyl- and 1,2,3-thiadiazolyl-5-carboxaldehydes [cf. (IIId)—(IIIh)]. In contrast, the
reaction stops at azomethine formation for benzimidazolylcarboxaldehyde (IV). In the
case of 2-thienyl- and 3-indolylcarboxaldehyde, the cyclization is accompanied by
elimination of the hetaryl unit [cf. (VII)]. — (BOGZA*, S. L.; KOBRAKOV, K. I.;
MALIENKO, A. A.; PEREPICHKA*, I. F.; SUJKOV, S. Y.; BRYCE, M. R.;
LYUBCHIK, S. B.; BATSANOV, A. S.; BOGDAN, N. M.; Org. Biomol. Chem. 3
(2005) 5, 932-940; Inst. Phys. Org. Coal Chem., Ukr. Acad. Sci., Donetsk 340114,
Ukraine; Eng.) — Mischke
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