Hybrid Synthetic and Computational Study of an Optimized, Solvent-Free Approach to Curcuminoids

A green and optimized
protocol has been developed for the preparation
of symmetric 1,7-bis­(aryl)-1,6-heptadiene-3,5-diones and asymmetric
2-aryl-6-arylidenecyclohexanones with modified substrate scope and
good functional group tolerance. Syntheses proceed smoothly under
solvent-free conditions, providing moderate to excellent product yields
with a minimal workup procedure. Control experiments, spectroscopic,
and computational studies support a mechanism involving the boron-assisted
in situ generation of imine intermediates. Crystal structures of three
curcuminoids and isolated mechanistic intermediates are reported.
The data provide insight for the further development of solvent-free
protocols toward diverse curcumin derivatives in the fields of pharmaceutical
and synthetic chemistries.