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Utilization of hypervalent iodine in organic synthesis: A novel and facile two‐step protocol for the synthesis of new derivatives of 1 H ‐Imidazo[1,2‐b]pyrazole by the cyclocondensation involving α‐Tosyloxyacetophenones
Author(s) -
Li Ming,
Yang Huazheng,
Zhao Guilong,
Wen Lirong,
Cao Wei,
Zhang Shusheng
Publication year - 2005
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.5570420205
Subject(s) - chemistry , hypervalent molecule , pyrazole , potassium carbonate , iodine , regioselectivity , combinatorial chemistry , medicinal chemistry , iodide , sodium iodide , organic chemistry , catalysis
Abstract A series of new 2‐aryl‐7‐cyano/ethoxycarbonyl‐6‐methylthio‐1 H ‐imidazo[1,2‐ b ]pyrazoles ( 5 ) have been synthesized in moderate to good yields, via a two‐step cyclocondensation procedure of 5‐amino‐4‐cyano/ethoxycarbonyl‐3‐methylthio‐1 H ‐pyrazole ( 1 ) and α‐bromoacetophenones ( 3 ) or α‐tosyloxyacetophenones ( 2 ), which were prepared by the reactions of acetophenones with [hydroxy(tosyloxy)iodo]benzene (HTIB). The intermediates, 5‐amino‐1‐(aroylmethyl)‐4‐ cyano/ethoxycarbonyl‐3‐methylthio‐1 H ‐pyrazoles ( 4 ), have been isolated, serving as evidence for the regioselectivity. When utilizing α‐tosyloxy‐acetophenones, the reactions were more eco‐friendly, the reaction time was significantly reduced and the synthetic procedure was more convenient and easier to manipulate. Surprisingly, using potassium carbonate to displace sodium carbonate in the synthesis of 4 , in the case of 1 (R CN), two novel cyclocondensation products have been isolated and fully characterized, followed by the proposal of a plausible mechanism.