Selectfluor-mediated mild oxidative halogenation and thiocyanation of 1-aryl-allenes with TMSX (X = Cl, Br, I, NCS) and NH4SCN

Presence of TMSX (X = Cl, Br, I) unleashes the oxidative character of Selectfluor and provides a mild dihalogenation method for 1-arylallenes. Preference for 2,3-addition was observed with TMSCl in MeCN irrespective of the nature of the substituent on the aryl moiety, whereas 1,2-addition was preferred in [BMIM][BF4]. With TMSBr and TMSI only products corresponding to 2,3-addition were observed. Reactions carried out with TMSBr in IL solvents gave the corresponding monobromoalkenes as a major product along with the isomeric dibromo-alkenes. Reaction with NH4SCN provided convenient access to dithiocyanate derivatives. The same products were formed via TMS-NCS/Selectfluor. Formation of common products via TMSNCS and NH4SCN points to the formation and interplay of SCN+/NCS+ as incipient electrophiles.

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