Synthesis of substituted dihydrobenzothiopyrans and dihydrobenzopyrans by cation-mediated cyclisation reactions

Treatment with acid of thiosalicylaldehyde- and salicylaldehyde-derived phenyl 3-phenyl-2-propenyl thioethers and ethers possessing latent oxonium ion functionality triggers simple or tandem cyclisation to give substituted dihydrobenzothiopyrans and dihydrobenzopyrans. Some derivatisation reactions of the products are described.