|Scheme 1: Synthesis of 4H-benzo[b]pyran derivatives under MW irradiation.|
Microwave-Assisted Three-Component “Catalyst and Solvent-Free” Green Protocol: A Highly Efficient and Clean One-Pot Synthesis of Tetrahydrobenzo[b]pyrans,
Sougata Santra, Matiur Rahman, Anupam Roy, Adinath Majee, and Alakananda Hajra
Volume 2014 (2014), Article ID 851924, 8 pages
A green and highly efficient method has been developed for the one-pot synthesis of tetrahydrobenzo[b]pyrans via a three-component condensation of aldehydes, 1,3-cyclic diketones, and malononitrile under MW irradiation without using any catalyst and solvent. This transformation presumably occurs by a sequential Knoevenagel condensation, Michael addition, and intramolecular cyclization. Operational simplicity, solvent and catalyst-free conditions, the compatibility with various functional groups, nonchromatographic purification technique, and high yields are the notable advantages of this procedure.
|Scheme 2: Plausible reaction mechanism.|