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Reduced 3,4′‐bipyrazoles from a simple pyrazole precursor: synthetic sequence, molecular structures and supramolecular assembly
Author(s) -
Cuartas Viviana,
Insuasty Braulio,
Cobo Justo,
Glidewell Christopher
Publication year - 2017
Publication title -
acta crystallographica section c
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.304
H-Index - 17
ISSN - 2053-2296
DOI - 10.1107/s205322961701302x
Subject(s) - chemistry , pyrazole , formic acid , acetic anhydride , substituent , stereochemistry , medicinal chemistry , organic chemistry , catalysis
The reaction of 5‐chloro‐3‐methyl‐1‐phenyl‐1 H ‐pyrazole‐4‐carbaldehyde and N ‐benzylmethylamine under microwave irradiation gives 5‐[benzyl(methyl)amino]‐3‐methyl‐1‐phenyl‐1 H ‐pyrazole‐4‐carbaldehyde, C 19 H 19 N 3 O, (I). Subsequent reactions under basic conditions, between (I) and a range of acetophenones, yield the corresponding chalcones. These undergo cyclocondensation reactions with hydrazine to produce reduced bipyrazoles which can be N ‐formylated with formic acid or N ‐acetylated with acetic anhydride. The structures of (I) and of representative examples from this reaction sequence are reported, namely the chalcone ( E )‐3‐{5‐[benzyl(methyl)amino]‐3‐methyl‐1‐phenyl‐1 H ‐pyrazol‐4‐yl}‐1‐(4‐bromophenyl)prop‐2‐en‐1‐one, C 27 H 24 BrN 3 O, (II), the N ‐formyl derivative (3 RS )‐5′‐[benzyl(methyl)amino]‐3′‐methyl‐1′,5‐diphenyl‐3,4‐dihydro‐1′ H ,2 H ‐[3,4′‐bipyrazole]‐2‐carbaldehyde, C 28 H 27 N 5 O, (III), and the N ‐acetyl derivative (3 RS )‐2‐acetyl‐5′‐[benzyl(methyl)amino]‐5‐(4‐methoxyphenyl)‐3′‐methyl‐1′‐phenyl‐3,4‐dihydro‐1′ H ,2 H ‐[3,4′‐bipyrazole], which crystallizes as the ethanol 0.945‐solvate, C 30 H 31 N 5 O 2 ·0.945C 2 H 6 O, (IV). There is significant delocalization of charge from the benzyl(methyl)amino substituent onto the carbonyl group in (I), but not in (II). In each of (III) and (IV), the reduced pyrazole ring is modestly puckered into an envelope conformation. The molecules of (I) are linked by a combination of C—H…N and C—H…π(arene) hydrogen bonds to form a simple chain of rings; those of (III) are linked by a combination of C—H…O and C—H…N hydrogen bonds to form sheets of R 2 2 (8) and R 6 6 (42) rings, and those of (IV) are linked by a combination of O—H…N and C—H…O hydrogen bonds to form a ribbon of edge‐fused R 2 4 (16) and R 4 4 (24) rings.