Synthesis of 3-Sulfenyl- and 3-Selenylindoles by the Pd/Cu-Catalyzed Coupling of N,N-Dialkyl-2-iodoanilines and Terminal Alkynes, Followed by n-Bu₄NI-Induced Electrophilic Cyclization

3-Sulfenyl- and 3-selenylindoles are readily synthesized by a two-step process involving the palladium/copper-catalyzed crossing coupling of N,N-dialkyl-ortho-iodoanilines and terminal alkynes and subsequent electrophilic cyclization of the resulting N,N-dialkyl-ortho-(1-alkynyl)anilines with arylsulfenyl chlorides or arylselenyl chlorides. The presence of a stoichiometric amount of n-Bu₄NI is crucial to the success of the electrophilic cyclization. A variety of 3-sulfenyl- and 3-selenylindole derivatives bearing alkyl, vinylic, aryl, and heteroaryl substituents have been prepared in good to excellent yields (up to 99%). By employing N,N-dibenzyl-ortho-iodoanilines, a 3-sulfenyl-N-H-indole has been successfully prepared. In addition, 3-sulfonyl- and 3-sulfinylindoles have also been successfully prepared by facile oxidation of the corresponding 3-sulfenylindoles.