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Reaction of Isocyanates and Isothiocyanates with Butyraldazine; Formation of 1‐Substituted 2‐Pyrazolines
Author(s) -
Zirngibl Ludwig,
Tam S. W.
Publication year - 1970
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19700530744
Subject(s) - chemistry , formic acid , pyrazoline , yield (engineering) , isothiocyanate , medicinal chemistry , catalysis , derivative (finance) , organic chemistry , phenyl isothiocyanate , materials science , economics , financial economics , metallurgy
Phenyl isothiocyanate reacts with butyraldazine in presence of acidic catalysts to form a 2‐pyrazoline (IV) whereas phenyl or benzyl isocyanates under similar conditions yield a mixture of the two isomeric 2‐pyrazolines XIa and XII. On reaction with Ac 2 O, IV gave the 1‐acetyl derivative V. Reduction with LiAlH 4 led to the corresponding pyrazolidines. Reexamination of Kost 's three step preparation of a 1‐phenylthiocarbamoyl 2‐pyrazoline [19] such as X via formic acid cyclization [18] of butyraldazine revealed that his first step product was apparently a mixture of two stereoisomeric 1‐formyl‐2‐pyrazolines VIIIa and VIIIb. A mechanism for the formation of these pyrazolines is proposed.