Chiral Auxiliary Approach for Gold(I)‐Catalyzed Cyclizations

Two different classes of stereoselective cyclizations have been developed using a chiral auxiliary approach with commercially available [JohnPhosAu(MeCN)SbF6] as catalyst. First, a stereoselective cascade cyclization of 1,5‐enynes was achieved using the Oppolzer camphorsultam as chiral auxiliary. In this case, a one‐pot cyclization‐hydrolysis sequence was developed to directly afford enantioenriched spirocyclic ketones. Then, the stereoselective alkoxycyclization of 1,6‐enynes was mediated by an Evans‐type oxazolidinone. A reduction‐hydrolysis sequence was selected to remove the auxiliary to give enantioenriched β‐tetralones. DFT studies confirmed that the steric clash between the chiral auxiliary and alkene accounts for the experimentally observed diastereoselective cyclization through the Si face. The stereoselective gold(I)‐catalyzed cascade cyclization of 1,5‐enynes and alkoxycyclization of 1,6‐enynes with chiral auxiliaries has been developed, affording, after hydrolysis, synthetically challenging enantioenriched ketones. This chiral auxiliary approach is an alternative to the use of complex chiral catalysts in gold(I)‐catalyzed asymmetric cyclizations.