Premium
Metalated Azolo[1,2,4]triazines. I. Synthesis of 2‐(6‐ tert ‐Butyl‐5‐oxo‐4,5‐dihydro‐1,2,4‐triazin‐3(2 H )‐ylidene)acetonitriles via Ring Opening Degradation of 3‐ tert ‐Butyl‐7‐lithio‐4‐oxo‐4 H ‐pyrazolo[5,1‐ c ][1,2,4]triazin‐1‐ides
Author(s) -
Ivanov Sergey M.,
Shestopalov Anatoliy M.
Publication year - 2019
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.3615
Subject(s) - chemistry , medicinal chemistry , stereochemistry
1,7,8‐Polymetalated 3‐ tert ‐butyl‐8‐R‐4‐oxo‐4 H ‐pyrazolo[5,1‐ c ][1,2,4]triazines (M = Li, Na; R = CO 2 Et, CN, H, D, and Li) have been generated for the first time using acidic NH deprotonation and lithium/bromine exchange method at −112 ÷ −97°C. The rapid pyrazole ring opening degradation of the unstable 7‐lithio‐4‐oxopyrazolo[5,1‐ c ][1,2,4]triazines at −97°C led to formation of 2‐(6‐ tert ‐butyl‐5‐oxo‐4,5‐dihydro‐1,2,4‐triazin‐3(2 H )‐ylidene)acetonitriles. Furthermore, lithium, sodium ((6‐ tert ‐butyl‐5‐oxo‐5 H ‐1,2,4‐triazin‐2,4‐diid‐3‐ylidene)(cyano)methyl)lithium was successfully generated from 7,8‐dibromo‐3‐ tert ‐butylpyrazolo[5,1‐ c ][1,2,4]triazin‐4(6 H )‐one, sodium hydride, and tert ‐butyl lithium, and an electrophile trapping using H 2 O, dimethylformamide, t ‐BuCOCl, and PhCOCl allowed the selective side‐chain functionalization. Structures of the isolated products have been established on the basis of IR, 1 H, 2 H, 13 C NMR, and high‐resolution mass spectra.