The Preparation of Lignans via Intermolecular Cycloadditions with Quinodimethanes ... John Mann* and Susan E. Piper Department of Chemistry, Reading University, Whiteknights, Reading RG6 2AD, U. K. ... Certain lignans can be prepared using, as the key step, a thermal reaction between 1 -(aryl)-l,3-dihydro-5,6- dialkoxy-benzo[c]thiophen 2,2-dioxides and dienophiles. ... Many naturally occurring lignans have interesting biological activities, for example (-)- ...