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Access to Some Angular Aminochromeno[2,3‐ c ]pyrazole Precursors by a Domino Knoevenagel–hetero‐Diels–Alder Reaction
Author(s) -
Parmar Narsidas J.,
Pansuriya Bhavesh R.,
Labana Balvantsingh M.,
Sutariya Tushar R.,
Kant Rajni,
Gupta Vivek K.
Publication year - 2012
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201200751
Subject(s) - chemistry , knoevenagel condensation , cascade reaction , ring (chemistry) , pyrazole , pyrazolones , domino , stereoselectivity , stereochemistry , organic chemistry , medicinal chemistry , catalysis
A new, solvent‐free tetrabutylammonium‐hydrogensulfate‐catalysed one‐pot procedure to synthesise angular benzopyran‐annulated pyrazoles, all of which incorporate a tertiary ring‐junction carbon, has been demonstrated. A typical intermediate Knoevenagel heterodiene, formed by the reaction of 2‐(alkenyloxy)‐ or 2‐(alkynyloxy)acetophenones with pyrazolones smoothly underwent a subsequent hetero‐Diels–Alder reaction to give chromeno‐fused pyrazoles in a highly stereoselective reaction. When nitro‐containing DKHDA products were treated further with Fe/HCl in tandem, they formed the corresponding amino frameworks in a reduction step, which highlights a new possibility for this cascade route to give aminopolyheterocycles. The stereochemistry of all new tertiary ring‐junction carbon‐containing polyheterocycles was confirmed by 2D NMR spectroscopy experiments, DQF‐COSY and NOESY, and single crystal X‐ray diffraction data. None of the products has had their biological profiled evaluated before, and they are expected to have heterosteroidal biological functions.