Fujiwara-Moritani-type reaction

Since the early reports of the Fujiwara-Moritani reaction [2], catalytic alkenylation procedures for a broad range of aromatic substrates with various alkenes have been developed. A proposed mechanism for these Fujiwara-Moritani-type reactions is illustrated in Scheme 18.4 [4]. The reaction is initiated by electrophilic attack on an arene by a cationic palladium species [PdOAc]+, generated in situ from Pd(OAc)2, to form an arylpalladium intermediate. Subsequent alkene insertion and fi-hydrogen elimination may occur to produce an alkenylarene derivative and HPdOAc. The latter may be reoxidized by an oxidant to regenerate Pd(OAc)2. 

The catalytic asymmetric Fujiwara-Moritani-type allylation reaction of indoles and pyrroles was reported by Oestreich and co-workers. Moderate yields and ee were realized by using novel oxazoline ligands and a stereo-genic quaternary center was formed (Scheme 5.12b). Nevertheless, it still leaves room for improvement, probably by designing new ligands. 

Ruthenium has a rich chemistry of hydroarylation reactions [22], but it has also been used successfully by Milstein and coworkers [23] as a catalyst for oxidative couplings of the Fujiwara-Moritani type (Figure 4.12). Under an atmosphere of carbon monoxide (6 bar), various ruthenium precursors effectively promoted the reaction of acrylates (e.g., 4g) with benzene (2a) to give a 1 1 ratio of the (E)-cinnamate 5i and methyl propionate 12, rather than the expected hydroarylation product methyl 3-phenylpropionate. Added oxygen (2 bar) could partly take over the role of the reoxidant from the alkene, resulting in an increase in the incorporahon of the alkene into the cinnamate product, giving a ratio of up to 3 1 of the arylated to the reduced acrylate. 

C-H alkenylation and decarboxylation (Scheme 4.48) [53], as in the reaction of benzoic acids described above (Schemes 4.28 and 4.29). Since the palladium-catalyzed Fujiwara-Moritani type direct alkenylation of indoles usually takes place at the C3-position, it enables alkenylation at a position complementary to that of the Fujiwara-Moritani reaction, being of unique synthetic utility. On the other hand, the reaction of thiophene-2-carboxylic acid leads to the formation of a mixture of C2- and C3-alkenylated products. Decarboxylation may take place too early to complete directed C-H alkenylation at the C3-position. In contrast, the exclusive C3-alkenylation on a thiophene ring is possible under rhodium catalysis (Scheme 4.49) [34b]. 

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... 

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

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. 

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

In feet, Norman et ol disclosed the first example of an intramolecular Fujiwara-Moritani reaction back in 1970 [124] it was. however, understood as a Friedel-Crafts-type process involving alkene activation by palladium(II). Aside from this seminal report, a few oxidative cydizations of 1.4-quinones using stoichiometric amounts of... 

Ru complexes catalyze the reaction between 2-aryl pyridines and alkenyl esters (Scheme 23.16) [75]. These types of olefins are often only slowly reacting substrates in oxidative Heck (Fujiwara-Moritani) reactions [18] thus, their use in Ru-catalyzed C-H olefinations is a remarkable advance. The shown reaction is overall redox neutral and produces 1 equivalent of alcohol or acid as side product. A variety of heterocyclic directing groups can be employed, and many functional groups are tolerated. However, the olefin scope of the reaction is somewhat limited to alkyl- and aryl-substituted alkenes. 

One remarkable reaction catalyzed by Rn complexes is the Murai conpling, in which alkyl arenes 44 are formed by hydroarylations of olefins. Interestingly, P-hydride elimination is not a problem in these reactions, as would be expected with other transition metal catalysts." " Murai-type protocols are especially nseful as they can employ electron-rich olefins, which are typically low-yielding snbstrates in Pd-catalyzed, oxidative Heck (Fujiwara-Moritani) reactions." " ... 

Prior to the concept of cross-dehydrogenative-coupling (CDC), Moritani and Fujiwara developed the oxidative formation of Heck-type reaction products directly from arenes and alkenes, instead of aryl halides and... 

Dehydrogenative Heck-type Reactions The Fujiwara-Moritani Reaction... 

Seheme 2.2 The Fujiwara-Moritani reaction or dehydrogenative Heck-type crosscoupling reaction. 

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