HECK-FUJIWARA Coupling

FUJI WAR A Lanthanide (Yb) reaction 136 FUJIWARA Aiylation, caiboxylation 137 FUJIWARA - HECK Coupling 138... 

After the finding of the coupling reaction via C—H activation, the couphng of olefins and aromatic halides by palladium catalysts was found as described in Part IV thus, these reactions are known as the Fujiwara arylationt or the Fujiwara-Heck reaction. fi i... 

Tsuji s group coupled 2-methylfuran with ethyl acrylate to afford adduct 15 via a Pd-catalyzed Fujiwara-Moritani/oxidative Heck reaction using tert-butyl peroxybenzoate to reoxidize Pd(0) to Pd(II) [30]. The palladation of 2-methylfuran takes place at the electron-rich C(5) in a fashion akin to electrophilic aromatic substitution. The perbenzoate acts as a hydrogen acceptor. 

The initial discovery of the oxidative Heck reaction was reported by Fujiwara and Moritani in 1967 when they disclosed the coupling of styrene with benzene in the presence of acetic acid and PdCl2 to give traws-stilbene and a-methylbenzyl acetate (Eq. (8.20)) [92]. Attempts to achieve catalytic turnover were made by adding Cu or Ag salts, but oidy 1-2 TONs were obtained [93]. 

In order to find alternative routes to functimial olefins via the very useful Heck reaction [52] oxidative dehydrogenative cross-coupling of sp C-H bonds with (alkene) C-H bond was first discovered using Pd(II) catalyst and an oxidant, by Moritani and Fujiwara [25,53], This oxidative alkenylation of aromatic C-H bonds profitably performed using cheap and stable mthenium(ll) catalysts was shown for the first time in 2011 successively by the groups of Satoh and Miura [54], Ackermann [55], Bruneau and Dixneuf [56], and Jegaiunohan [57] [(Eq. 2)]. This Ru(n)-catalysed alkenylation reaction offers a potential to reach a large variety of functional alkenes at low cost and has been extended to annulation reactions with alkynes for a fast access to heterocycles. 

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... 

The groundbreaking work of Shue, de Vries and van Leeuwen others on oxidative olefinations and the contributions of Lu, Fagnou, DeBoef and others on direct arylations laid the foundation for the development of an impressive number of transition-metal-catalyzed selective cross-dehydrogenative sp C-H couplings. Notably, the Fujiwara-Moritani reaction is also commonly termed the oxidative Mizoroki-Heck reaction . Progress in this area has been extensively reviewed and will thus only be briefly mentioned here, notwithstanding their great importance. 

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. 

The Fujiwara-Moritani reaction enables the coupling of alkenes with arenes under oxidative conditions—also named oxidative Heck reaction (for the mechanism, see Ref [ 29]) Garcia-Rubia et al. used this Pd"-catalyzed oxidative direct C-H alkenylation to produce /rans-stilbene derivatives.As exemplified by their synthesis of pterostilene (Scheme 5-45), a partially methylated resveratrol derivative, a 2-pyridyl sulfinyl group efficiently promotes the Pd"-catalyzed ortho C-H olefination of arenes and can be readily removed or transformed into a thiol group. 

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