Aldonitrones as Aldehyde Equivalents: An Efficient, Green, and Novel Protocol for the Synthesis of 1,8-Dioxo-octahydroxanthenes

Abstract

A novel, self-catalyzed, solvent-free, microwave-enhanced, green, and efficient protocol for the synthesis of 1,8-dioxo-octahydroxanthenes and bis-5,5-dimethyl-1,3-cyclohexanediones by condensing aldo-nitrones (imine oxide) and dimedone (5,5-dimethyl-1,3-cyclohexanedione) under microwave irradiation is disclosed. Product formation (viz. xanthenes and bis-5,5-dimethyl-1,3-cyclohexanediones) is dependent on reaction conditions. The entire process is green and sustainable in terms of solvents, chemicals, reaction procedure, and yields. A plausible reaction mechanism of this reaction is also proposed.

Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for full experimental and spectral details.

GRAPHICAL ABSTRACT

Keywords:

• Bis-5,5-dimethyl-1,3-cyclohexanediones
• dimedone (5,5-dimethyl-1,3-cyclohexanedione)
• 1,8-dioxo-octahydroxanthenes
• microwave irradiation (MWI)
• nitrones
• solvent-free

ACKNOWLEDGMENTS

The authors are thankful to the Council of Scientific and Industrial Research, New Delhi, India, for financial assistance and to the Indian National Science Academy for additional financial support for this research project. The authors are also thankful to the Sophisticated Analytical Instrument Facility Central Instrument Laboratory (SAIF-CIL), Panjab University, Chandigarh, for spectral analysis.

Notes

^a Reaction conditions: 1 (10 mmol), 2 (20 mmol), and solvent (10 mL) stirred at rt. PEG stands for polyethylene glycol.

^a The products were characterized by comparison of their melting points and spectral (IR, ¹H NMR) data with those of authentic samples. A and B stand for reaction conditions H₂O, rt and EtOH, rt, respectively.

^a Reaction conditions: A mixture of 1 (10 mmol), 2 (20 mmol), and solvent (5 mL) was irradiated under MWI.

^a The products were characterized by comparison of their melting points and spectral (IR, ¹H NMR) data with those of authentic samples. A and B stand for reaction conditions solvent-free, MWI and PEG, MWI, respectively.