Palladium-Catalyzed, Modular Synthesis of Highly Functionalized Indoles and Tryptophans by Direct Annulation of Substituted o-Haloanilines and Aldehydes

One-pot synthesis of indoles by a palladium-catalyzed annulation of o-haloanilines and aldehydes has been developed. Coupling of o-iodoaniline with aldehyde is realized under mild ligandless conditions [Pd(OAc)2, DABCO, DMF, 85 DegC], whereas X-Phos is found to be the ligand of choice for coupling reactions involving o-chloroanilines/o-bromoanilines and aldehydes. A variety of o-haloanilines with different electronic properties are suitable substrates, and aldehydes including chiral ones participated in this reaction without racemization. Coupling of (S)-2-N,N-di-tert-butoxycarbonyl-5-oxopentanoate, derived from L-glutamic acid, with o-haloanilines provides a rapid access to the ring-A-substituted tryptophans in good to excellent yields. [on SciFinder (R)]