The Pechmann dehydration reaction of cyclohexanone derivatives with phenols yields coumarin‐fused cyclohexadiene intermediates.

In the presence of trifluoroacetic acid and methanesulfonic acid (MSA), a series of monohydric and polyhydric phenols readily undergo a domino Pechmann-dehydration reaction with various 4-hydroxy-6-oxocyclohexane-1,3-dicarboxylates to give 7,8-dihydro-6H-dibenzo[b,d]pyran-6-ones. Subsequent dehydrogenation of the 7,8-dihydro-6H-dibenzo[b,d]pyran-6-ones was performed expediently with DBU/BrCCl 3 to give various 6H-dibenzo [b,d]pyran-6-one derivatives. This strategy has the advantages of inexpensive and easily available raw materials, metal-free procedure, mild reaction conditions, good compatibility with various functional groups, and satisfactory yields.