Intermolecular Direct Annulation To Functionalized Indoles From Ortho-Haloanilines And Ketones Catalyzed By Well-defined NHC-Pd Complexes (NHC=N-Heterocyclic Carbene)

Since the first stable N-heterocyclic carbene was isolated by Arduengo and co-workers in 1991, invetsigation of N-heterocyclic carbene metal complexes has been received rapidly increasing interest and this field has become a focal point of organic chemistry in recent years.. Because of their special coordination chemistry, N-heterocyclic carbene both stabilizes and activates metal centers, which makes them highly catalytic activity in C-C bond and C-N bond formation. In particular, NHC ligands derived from imidazolium salts have an increasing use in organometallic chemistry and homogeneous catalysis, and have shown additional advantages to the widely used phosphine ligands.In this thesis, several types of well-defined NHC-Pd complexes, including (IPr)Pd(allyl)Cl (A),(IPr)Pd(cinnamyl)Cl (B), (IPr)Pd(Cp)Cl (C), (IPr)Pd(PPh3)Cl2 (D), (IPr)Pd(3-chloropyridine)Cl2(E), (IPr)Pd(acac)Cl (F), Pd(SIPr)(OAc)2(H2O)(G) are prepared according to the described methods. Their catalytic potential in the direct annualtion to indoles from o-haloanilines with simple ketones was investigated and compound (F) found to be superior precatalyst for this transformation.(IPr)Pd(acac)Cl (F) not only in the direct annulation of o-bromo anilines with ketones for indole synthesis, but also in the reaction of deactived o-chloroaniline with ketones has shown excellent catalytic activity.Compared with the corresponding catalytic protocol of phosphine-Pd complex, the strategy for indole synthesis described here only needs a less catalyst loading and lower reaction temperature and stands for a more economical and industrial applicable procedure.