The Intramolecular <i>Ramberg</i>‐<i>Bäcklund</i> Reaction: A Convenient Method for the Synthesis of Strained Bridgehead Olefins

Abstract

Abstract The stereochemical aspects of the intramolecular Ramberg ‐ Bäcklund reaction, i.e. the 1,3‐elimination of hydrogen halide followed by sulfur dioxide extrusion, have been studied on the α‐bromosulfones of the 1‐thiadecalin Throughout this paper ‘1‐thiadecalin’ will be used in place of ‘decahydro‐1‐thianaphthalene’. series. Whereas the cis , exo ‐bromosulfone 23a containing the ideal W‐type arrangement of the reacting atoms undergoes a clean Ramberg ‐ Bäcklund reaction, the trans , exo ‐ and trans , endo ‐bromosulfones, 24a and 24b , respectively, lead to an α,β‐unsaturated sulfone by simple 1,2‐elimination of HBr. Application of the Ramberg ‐ Bäcklund reaction to 9‐bromo‐8‐thiabicyclo[5.2.1]decane‐8,8‐dioxide ( 17 ) permits a short synthesis of the Bredt olefin bicyclo[5.1.1]non‐1(8)‐ene ( 5 ), which can be isolated but shows the typical high reactivity of other methylene‐bridged ( E )‐cyclooctenes.