Enantioselective 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. 

3 Intermolecular Fujiwara-Moritani Reactions via Directing Groups 

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, 

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Oxidative Heck-Type Reactions (Fujiwara Moritani Reactions) 357 9.2.3 Enantioselective Fujiwara—Moritani Reactions... 

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. 

In 1999, Mikami s group reported the first example of an intermolecular asymmetric Fujiwara-Moritani reaction of benzene with cyclic alkenes using a Pd catalyst co-ordinating to a chiral sulfonylamide-oxazoline ligand (Scheme 7.24). With PhCOs Bu as the oxidant, the coupling reaction occurred with moderate enantioselectivity (up to 49% ee), although the chemical yield was low. The reaction is considered to involve the formation of a phenyl-Pd species via electrophilic C-H substitution by Pd(ii), and Heck-type cyclization followed by re-oxidation of the resultant Pd(0) species. 

Oestreich and co-workers reported an enantioselective intramolecular Fujiwara-Moritani reaction of indole and pyrrole derivatives. Using a suitable oxidant e.g., PhCOg Bu, benzoquinone, O2), they evaluated a chiral bidentate pyridyl-oxazoline ligand (PyOx) developed by Stolz and a series of nicotine-oxazoline ligands (NicOx) with Pd(OAc)2 as a catalyst precursor (Scheme 7.25). Indoles and pyrroles underwent a 5-exo-trig cyclization, but the chemical yield and enantioselectivity were generally unsatisfactoiy. 

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