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. (c) 2005 Elsevier Ltd. All rights reserved.