Synthesis of 3-exo-aroylhexahydroindoles via sequential gold(I)-catalyzed claisen-type rearrangement-epimerization reactions of cis -4-[ N -Tosyl- N -(3-arylprop-2-ynyl)amino]cyclohex-2-en-1-ols

A two-step process for the synthesis of 3-exo-aroylhexahydroindoles is described. cis-4-[N-Tosyl-N-(3-arylprop-2-ynyl)amino]cyclohex-2-en-1-ols were cycloisomerized with a catalytic amount of chloro(triphenylphosphine)gold(I)/ silver(I) hexafluoroantimonate (AuPPh₃Cl/AgSbF₆); subsequent base treatment of the crude mixture provided 3-exo- aroylhexahydroindoles in good yields and complete stereoselectivity. A key step involving a 9-endo-dig attack of the hydroxyl group onto the gold-activated alkyne is proposed. The resulting allyl vinyl ether intermediate underwent a gold-assisted [3,3]-sigmatropic rearrangement to form 3-exo-3- aroylhexahydroindole derivatives.