1‐Substituted 1,3‐Dihydroisothianaphthen‐2,2‐dioxides: Preparation and Use as ortho‐Quinodimethane Precursors in Intramolecular Cycloadditions. Preliminary communication

Abstract 1,3‐Dihydroisothianaphthen‐2,2‐dioxide (1) was readily converted to the 1‐substituted sulfones 3 by deprotonation and subsequent electrophilic attack ( Scheme 3 and Table ). The appropriate 1‐alkenyl‐ and 1‐alkenoyl‐sulfones 3 on heating at 213° to 240° underwent SO 2 ‐extrusion to give, via the non‐isolated ( E )‐quinodimethanes II ( Scheme 1 ), polycyclic products such as 4, 6 and 7 in good yields ( Schemes 4 and 5 ). On the other hand, thermolysis of the 1‐alkenoyl‐1‐thioether sulfones 9 furnished mainly the isochromenes 10 ( Scheme 6 ).