Cycloaddition Behavior of Electron‐Poor 1,2‐Thiaphospholes

The acceptor‐substituted 1,2‐thiaphospholes 1 react regioselectively with the electron‐rich acetylenes 2 at −78 °C by [2+2] cycloaddition to afford the novel heterobicyclic compounds 4 . As demonstrated by the examples of their reactions with nonacarbonyldiiron( 0 ) and the pentacarbonyltungsten fragment, compounds 4 are able to function as ligands in complex compounds. In addition, the electron‐rich double bond in the bicyclic compound 4a is amenable to further reactions. Hence, treatment with mesitylenecarbonitrile oxide ( 7 ) proceeds through a chemo‐, regio‐, and stereoselective [3+2] cycloaddition to afford the novel heterocyclic system 8 . On the other hand, the heterocyclic compounds 1a , 1d , 1e , and 1i react with 2 equiv. of cyclooctyne ( 9 ) only at 100 °C, to afford the sulfur‐containing phosphabarrelenes 10 , together with the tricyclic compounds 11 . (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)