Convenient Synthesis of 3-Methylcoumarins and Coumarin-3-carbaldehydes

Abstract

Rapid, microwave-assisted Baylis–Hillman reactions of substituted salicylaldehydes, followed by one-pot hydrogen iodide–mediated cyclization and reduction of the corresponding adducts, has afforded 3-methylcoumarins in up to 94% yield in the final step. Subsequent microwave-assisted selenium dioxide oxidation of selected 3-methylcoumarins has provided convenient access to the corresponding coumarin-3-carbaldehydes and permitted a significant improvement over the yield obtained using conventional heating.

GRAPHICAL ABSTRACT

Keywords:

• Baylis–Hillman reactions
• coumarin-3-carbaldehydes
• 3-methylcoumarins
• microwave-assisted reactions

ACKNOWLEDGMENTS

The authors thank Rhodes University for a bursary (to T. O. O.), the South African Medical Research Council (MRC) and Rhodes University for generous financial support, and Nathan Rose for analytical data for compound 6c.^{[ 25 ]}