Moritani-Fujiwara reaction

Mikami and co-workers reported the first examples of an asymmetric Fujiwara-Moritani reaction," which is generally catalyzed by chiral Pd(II) complexes... 

Arenes, especially electron-rich ones, have been found to react with alkynes in the presence of Pd(ll) or Pt(ll) species in a mixed solvent containing CF3COOH (Eq. 81) [158-160]. The intramolecular reaction is also possible (Eq. 82). The mechanism proposed for the reaction involves aromatic pallada-tion to form arylpalladium species as in Fujiwara-Moritani reaction, insertion of an alkyne, and protonolysis of the resulted vinylpalladium intermediate. 

C-H bond activation and C-C bond formation are the key issues in organic synthesis [150-156]. The so-called Fujiwara-Moritani reaction has been regarded as one of the most versatile methods for activation of aromatic C-H bonds to provide a coupling product with an olefin using a catalytic amount of Pd(II) complex with an equimolar amount of a reoxidant [157-159]. 

By using an LX-type ligand, the catalytic asymmetric Fujiwara-Moritani reaction of benzene with cyclic olefins can afford the chiral phenyl-substituted cyclic olefins through syn p-H elimination from the opposite (y) side to the phenyl group (Scheme 32) [160]. 

Complexes 24, 25, and 26 aU possess two neutral and two anionic ligands, respectively, and they are included in this section although they do not have halide ligands. Each of C2-symmetric bisoxazoline complexes 24 and 25 has two tiifluoroacetate ligands and is a good catalyst for asymmetric Wacker-type cyclization. Complex 26, applied to the asymmetric Fujiwara-Moritani reaction, is a rare example of having anionic chelate... 

In 1999, Mikami and co-workers reported the first example of asymmetric Fujiwara-Moritani reaction catalyzed by Pd" and sulfonylamino-oxazoline ligand (Scheme 5.12a). A 1 1 complex between the chiral ligand and Pd(OAc)2 could be the active catalyst in this asymmetric Fujiwara-Moritani reaction. This method provides a convenient process to synthesize aromatic C—H bond activation/olefin coupling products but with moderate enantioselectivity. 

Scheme 5.12 Pd-catalyzed asymmetric Fujiwara-Moritani reaction reported by Mikami and Oestreich.

Scheme 5.39 The first asymmetric intramolecular Fujiwara-Moritani reaction reported by Mural.

Oxidative Heck-Type Reactions (Fujiwara-Moritani Reactions)... 

Intermolecular Fujiwara-Moritani Reactions via Electrophilic Palladation... 

Figure 9.2 The proposed mechanism of the Fujiwara-Moritani reaction.

Compared with the numerous developments of catalytic asynunetric reactions with chiral palladium(O) catalysts [ lc,e], catalytic asynunetric reactions by chiral palladium(ll) species have so far received only little attention, hi fact, the enantioselective Fujiwara-Moritani reaction still remains a significant challenge for organic chemists. Little success has been achieved thus far, presumably because of the inherent nature of the reaction, where styrene-type products absent of chiral centres arc typically formed from the -hydride elimination process. 

Unlike the previously discussed Fujiwara-Moritani reactions, which involve the electrophilic palladation of arenes, another category of Fujiwara-Moritani reactions exists that takes advantage of the directing ability of a neighbouring functional group. De Vries and coworkers [32] have reported a selective palladium(ll)-catalysed oxidative coupling of anilides with alkenes through C-H bond activation at room temperature. It was found that acetanilide (54) reacts with -butyl acrylate (4d) in the presence of 2 mol% Pd(OAc)2,... 

In addition to the several reports of intermolecular Fujiwara-Moritani reactions, there have been a nnmber of examples of intramolecular reactions, both stoichiometric and catalytic in palladinm. In considering an intramolecular oxidative Heck reaction, one can again draw a direct analogy to the classical Heck reaction (Figure 9.3). In the standard Heck reaction, a halogenated arene nndergoes an oxidative addition by palladium(0), followed by alkene insertion and jS-hydride elimination. In an oxidative version, a C—H bond of... 

Intramolecular Fujiwara-Moritani Reactions Stoichiometric in Palladium... 

In order to elucidate the mechanism of this reaction, a substrate probe was designed. Diastereomerically pure indole 140 was synthesized and subjected to the aerobic oxidative cyclization (Scheme 9.20). Annulated indole 141 was produced as a single diastereomer. The outcome of this reaction strongly suggested a mechanism involving initial palladation of the indole, followed by alkene insertion and )3-hydride elimination (an intramolecular Fujiwara-Moritani reaction). If the reaction proceeded by alkene activation followed by nucleophilic attack of the indole, then the opposite diastereomer would have been observed. This experiment confirmed that an oxidative Heck reaction pathway was operative in this aerobic indole annulation. 

Oxidative Heck-Type Reactions (Fujiwara-Moritani Reactions) 373 Table 9.2 The palladium-catalysed oxidative cyclization of aryl allyl ethers oxidant studies. 

For reviews on the Fujiwara-Moritani reaction, see (a) Fujiwara, Y. (2002) Palladium-promoted alkene-arene coupling via C—H activation, in Handbook of Organopalladium Chemistry in Organic Synthesis, Vol. 2 (eds E.-i. Negishi and A. de Meijere), John Wiley Sons, Inc., New York, pp. 2863-71 (b) Jia, C., Kitamura, T. and Fujiwara, Y. (2001) Catalytic functionalization of arenes and alkanes via C—H bond activation. Acc. Chem. Res., 34, 633-9 (c) Fujiwara, Y. and Jia, C. (2001) New developments in transition metal-catalyzed synthetic reactions viaC—H bond activation. PureAppl. Chem., 73,319-24 (d) Moritani, I. and Fujiwara, Y. (1973) Aromatic substitution of olefins by palladium salts. Synthesis, 524-33. 

Mikami, K., Hatano, M. and Terada, M. (1999) Catalytic C—H bond activation-asymmetric olefin coupling reaction the first example of asymmetric Fujiwara-Moritani reaction catalyzed by chiral paUadium(II) complexes. Chem. Lett., 28, 55-6. 

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