3-Substituted 2-Isothiocyanatoacrylic Esters

✍ Scribed by Dr. Dieter Hoppe

• Publisher: John Wiley and Sons
• Year: 1973
• Tongue: English
• Weight: 233 KB
• Volume: 12
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/anie.197309231

✦ Synopsis

spectra. If these products ( 3 ) are heated in glacial acetic acid, they afford 5,6-cycloalkeno-1 H-pyrazolo [3,4-b]pyridines ( 4 ) whose structures follow especially from their I3C chemical shifts and the I3C-lH coupling constants of the carbon atoms of the pyridine ring: the unsubstituted carbon atom C-4 of the 5,6-cycloalkeno-l H-pyrazolo[3,4blpyridines obtained appears as a doublet at 6= -128 ppm with a coupling constant J,,~155-160 Hz. These values accord with the 6 and J,, data found for C-4 of pyridines''], in contrast to 6%-145 to -150 ppm and J,,-150 to 175 Hz found for C-2 of pyridines. which fragment to ( 4 ) and diphenyl phosphate (variant A) (Table 1).

1 H-Pyrazolo[ 3,4-b]pyr id ines ( 4 )

Compounds ( I ) (0.02mol) and (2) (0.02mol) are heated together under reflux in glacial acetic acid for 24h. If the product ( 4 ) does not crystallize on cooling, isolation is achieved by variant A, B or C below. Varianr A : The reaction mixture is treated cautiously with water. The precipitate is collected and recrystallized from ethanol/water. Variant B : The reaction mixture is treated with sodium hydroxide solution until alkaline. The oil that separates is extracted with ether. After removal of the ether in a rotary evaporator the residue is recrystallized from ethanol/water. Variant C: The acetic acid is distilled off and the oil is distilled at ca. 0.1-0.9 torr.