Abstract
This comprehensive study describes the influence of substituents at the aryl moiety on SmI~2~‐mediated intramolecular ketyl–aryl coupling reactions. Differently substituted γ‐aryl ketones were employed as precursors, which were directly prepared by Heck reactions of 4‐penten‐2‐ol with the corresponding bromo‐ or iodobenzenes. After treatment with two equivalents of samarium diiodide γ‐aryl ketones bearing electron‐withdrawing substituents such as cyano, trifluoromethyl or carbonyl groups gave the expected hexahydronaphthalene derivatives as single diastereoisomers in most cases. The position of the substituents was also of crucial influence on the outcome; in several cases ipso‐substitution leading to the formation of spiro compounds was observed. Electron‐donating substituents at the aromatic moiety are less favourable for the ketyl–aryl couplings. They apparently impede the second electron transfer that is involved in this multi‐step process. On the basis of these observations the mechanism of the SmI~2~‐promoted ketyl–aryl couplings is discussed in detail. For precursors with electron‐withdrawing substituents in m‐position fairly stabilized carbanionic intermediates of the SmI~2~‐promoted cyclization could be trapped with acetone or allyl bromide as electrophiles to regioselectively provide the corresponding addition products. Our results should be valuable for synthetic applications of the stereoselectively generated hexahydronaphthalene derivatives.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)