Paal-Knorr fiiran synthesis


Paal-Knorr Furan Synthesis  [c.159]

Paal-Knorr Furan Synthesis  [c.168]

Treatment of 1,4-dicarbonyls (1) with catalytic acid yields substituted furans (2) and is called the Paal-Knorr furan synthesis. This method is used extensively to produce a variety of mono-, di-, tri-, and tetrasubstituted furans.  [c.168]

Separately, Paal and Knorr described the initial examples of condensation reactions between 1,4-diketones and primary amines, which became known as the Paal-Knorr pyrrole synthesis. Paal also developed a furan synthesis in related studies. The central theme of these reactions involves cyclizations of 1,4-diketones, either in the presence of a primary amine (Paal-Knorr pyrrole synthesis), in the presence of a sulfur(II) source (Paal thiophene synthesis), or by dehydration of the diketone itself (Paal furan synthesis).  [c.207]

Although nearly all Paal-Knorr condensations produce di-, tri-, or tetrasubstituted furans, it is possible to use this reaction to generate monosubstituted furans. Molander demonstrated the utility of this method with his synthesis of 2-(methyldiphenylsilyl)furan (11) from dicarbonyl 10.  [c.169]

The mechanism of the Paal-Knorr furan synthesis was investigated by Amamath in 1995. ° After detailed kinetic studies involving the d,l and meso diastereomers of 2,3-disubstituted 1,4-diketones (5) the following mechanistic pathway emerged. One of the carbonyls is reversibly protonated by the catalytic acid to yield 6. Next, in the rate-determining step, water removes the proton adjacent to the unprotonated ketone which triggers simultaneous alkene formation and attack of the protonated ketone to form dihydrofuran 7. Protonation of the alcohol in 7 to furnish cation 8 followed by elimination of water produces the furan product 9 and regenerates the acid catalyst. This is slightly different than the standard mechanistic proposal that involved a two-  [c.168]

Ibers used the Paal-Knorr furan synthesis to prepare a key intermediate for the synthesis of novel porphyrin-like aromatic macrocycles. Bis yrolyljfuran 27 was available in good yield via the acid catalyzed condensation of diketone 26.  [c.171]

The Paal-Knorr furan synthesis can also be used to prepare 2,5-arylalkylfurans, as illustrated in the following example. Salimbeni produced furan 29 from dione 28 and subsequently used the furan as an intermediate for the production of angiotensin II receptor antagonists.  [c.171]

PAAL - KNORR Pyrrole Synthesis Pyrrole synthesis from 1,4-butanedlone and amines.  [c.284]

Paal-Knorr synthesis, 4, 118, 329 Pariser-Parr-Pople approach, 4, 157 PE spectroscopy, 4, 24, 188-189 photoaddition reactions with aliphatic aldehydes and ketones, 4, 232 photochemical reactions, 4, 67, 201-205 with aliphatic carbonyl compounds, 4, 268 with dimethyl acetylenedicarboxylate, 4, 268 Piloty synthesis, 4, 345 Piloty-Robinson synthesis, 4, 110-111 polymers, 273-274, 295, 301, 302 applications, 4, 376 polymethylation, 4, 224 N-protected, 4, 238 palladation, 4, 83 protonation, 4, 46, 47, 206 pyridazine synthesis from, 3, 52 pyridine complexes NMR, 4, 165  [c.819]


See pages that mention the term Paal-Knorr fiiran synthesis : [c.161]    [c.118]    [c.178]    [c.112]   
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Name reactions in heterocyclic chemistry  -> Paal-Knorr fiiran synthesis