Microwave-assisted rapid cyclization of lapachol, a main constituent of Heterophragma adenophyllum

Abstract

Cyclization reactions of lapachol (1) isolated from Heterophragma adenophyllum have been studied under microwave irradiation under different conditions using alumina (acidic, basic and neutral)/silica gel/montmorillonite (KSF and K-10) as solid support along with neat reaction using 2–3 drops of DMF giving naturally occurring dehydro-α-lapachone (2), α-lapachone (3), β-lapachone (4) depending upon the nature of support and irradiation time. A novel naphthoquinone derivative adenophyllone (5) can be synthesized from lapachol using DMF under microwaves.

Keywords:

• Heterophragma adenophyllum
• Lapachol
• Dehydro-α-lapachone
• α-Lapachone
• β-Lapachone
• Adenophyllone
• Microwave technique

Acknowledgements

Financial assistance from UGC (New Delhi) is gratefully acknowledged. We are also thankful to RSIC, CDRI, Lucknow for recording the spectra.