Regiocontrolled 1,2-migration in cyclization of 1-(indol-2-yl)-3-alkyn-1-ols: (Ph ₃ P)Au ⁺ vs. PtCl ₄

An AuCl(PPh3)/AgBF4- and PtCl4-catalyzed reaction of 1-(indol-2-yl)-3-alkyn-1-ols occurred smoothly in toluene to form a series of differently polysubstituted carbazole derivatives efficiently. The regioselectivity of the 1,2-migration may be tuned by using different metal catalysts: carbazoles 3 could be obtained exclusively in the presence of AuCl(PPh3)/AgBF4via a Wagner–Meerwein type 1,2-alkyl shift, whereas in some cases the use of PtCl4 afforded differently substituted carbazoles 4 involving a platinum–carbene intermediate.