Heterocyclen durch Michael‐Reaktionen, 5. Mitt. Nucleophile Additionen an 4‐Aryliden‐pyrazolone

Abstract

Arylidenpyrazolone 1 reagieren mit aktiven Methylenverbindungen wie Malonsauredinitril, Malonestern, Cyanessigestern oder Cyanacetamid zu den Addukten 2,4,8 und 10. Die basenkatalysierte Cyclisierung gelingt nur bei 2, in allen anderen Fallen lafit sie sich nicht erreichen. Hingegen fuhrt Cyclisierung von 8 und 10 in Gegenwart von Saure zu den bisher unbekannten tricyclischen Systemen 16 und 18. Heterocycles via Michael Reaction, V1): Nucleophilic Additions t o QArylidenepyrazolonesThe adducts 2,4,8 and 10 were obtained from the arylidenepyrazolones 1 and reactive methylene compounds, such as malononitrile, alkyl malonates, alkyl cyanoacetates or cyanoacetamide.Cyclisation with basic catalysis was successful with compound 2 only. On the other hand, cyclisation of 8 and 10 in the presence of acids yielded the hitherto unknown tricyclic systems 16 and 18.

Complete Catalytic Deoxygenation of CO2 into Formamidine Derivatives

“…Some heterocyclic compounds containing condensed pyrazoles such as pyrano[2,3‐ c ]pyrazoles possess a wide spectrum of pharmacological action, including analgesic, anti‐inflammatory, vasodilating and antihypertensive activities [19–21]. Hence, the preparation and biological properties of new substituted pyrano[2,3‐ c ]pyrazoles are of interest [22–36]. For these reasons, we focused our attention on the development of a new method for the preparation of pyrano[2,3‐ c ]pyrazoles starting from spirocyclopropanepyrazoles and now report the results of our investigation, a ring‐opening/cyanomethylation and intramolecular cyclization of them in the presence of a base such as sodium hydride.…”

Organocatalyzed enantioselective synthesis of 6-amino-5-cyanodihydropyrano[2,3-c]pyrazoles

“…1g Due to their biological significance,1 there has been considerable interest in developing synthetic methods for 6-amino-5-cyanodihydro-pyrano[ 2,3- c ]pyrazoles 2–6. These compounds may be readily obtained from the reaction of 4-arylmethylene-5-pyrazolone and malononitrile, 2,3 or 2-pyrazolin-5-ones and benzylidenemalononitriles 3. The overall reaction is a tandem Michael addition and a Thorpe-Ziegler type reaction (an enol addition to a cyano group) followed by tautomerization 3.…”

“…It should be pointed out that these compounds may exist in the 1,4-dihydro or 2,4-dihydro tautomeric forms when the N1 position is unsubstituted. Although most studies assigned the 1,4-dihydro structure to these derivatives,2–4 recent X-ray crystallographic data prefer the 2,4-dihydro tautomer 5,6…”

A Review on the Recent Multicomponent Synthesis of Pyranopyrazoles

“…In a further report, Otto and Schmelz showed that weak bases can also be utilized for a Michael-type cyclization. 36 This work was extended by Klokol et al who performed the direct conversion of 3methyl-3-pyrazolin-5-one with malononitrile in the presence of a weak base. 37 The multicomponent synthesis of pyranopyrazoles Using catalyst-free conditions Shaabani et al 38 described a three-component reaction for the synthesis of pyranopyrazoles using acetylenedicarboxylate, isocyanides, and 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one (Scheme 1).…”