Access to Some Angular Aminochromeno[2,3-c]pyrazole Precursors by a Domino Knoevenagel-hetero-Diels-Alder Reaction

• Published in: European journal of organic chemistry 2012-10, Vol.2012 (30), p.5953-5964
• Main Authors: Parmar, Narsidas J., Pansuriya, Bhavesh R., Labana, Balvantsingh M., Sutariya, Tushar R., Kant, Rajni, Gupta, Vivek K.
• Format: Article
• Language: English
• Subjects: Chemistry; Cycli­zation; Diffraction; Domino reactions; Exact sciences and technology; Heterocyclic compounds; Heterocyclic compounds with n hetero atom and also o and/or s, se, te hetero atoms; Heterocyclic compounds with o, s, se, te hetero atom and condensed derivatives; Heterocyclic compounds with several n hetero atoms in the same ring, in separated rings or in fused rings; Nitrogen heterocycles; Noncondensed benzenic compounds; One-pot reactions; Organic chemistry; Oxygen heterocycles; Preparations and properties; X-rays
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201200751

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. A solvent‐free, tetrabutylammonium‐hydrogensulfate‐catalysed method to synthesise angular aminobenzopyrano[2,3‐c]pyrazole precursors by a domino Knoevenagel–hetero‐Diels–Alder (DKHDA) reaction has been developed. When nitro‐containing DKHDA products were treated further with Fe/HCl in tandem, they smoothly underwent a subsequent reduction, facilitating access to aminobenzopyran annulated products by this cascade route.