PALLADIUM-CATALYZED CYCLIZATION OF O-ALKYNYLTRIFLUOROACETANILIDES WITH ALLYL ESTERS - A REGIOSELECTIVE SYNTHESIS OF 3-ALLYLINDOLES

The reaction of readily available o-alkynyltrifluoroacetanilides 1 wit h allyl esters provides a valuable new route to 3-allylindoles 3. Thre e basic procedures have been developed: a stepwise method based on the isolation of the N-allyl derivative 4 and its subsequent cyclization to 3 (procedure a), a one-pot reaction omitting the isolation of 4 (pr ocedure b), and a procedure which most probably leads to the formation of 3 through a mechanism not involving the intermediacy of 4 (procedu re c). In the presence of the electron-rich sterically encumbered liga nd tris(2,4,6-trimethoxyphenyl)phosphine (ttmpp) the reaction exhibits remarkable regioselectivity and almost exclusive formation of 3-allyl indoles with the indolyl moiety bound to the less substituted allyl te rminus is usually observed. However, some loss of olefin geometry is o bserved.