Allyl arenes, oxidative transformation

The mechanism (Scheme 5) of the oxidative C-H transformation of allyl arenes to alkenyl aldehydes by 2,3-dichloro-5,6-dicyano-l,4-benzoquinone (37) and catalysed by FeCl2 in C2H4CI2 had the initial reaction in which (37) oxidized allyl benzene (38), or [(Z)-prop-l-enyl]benzene (39), assisted by FeCl2, through a singleelectron transfer to the corresponding allyl radical (40) and Fe(IIl) complex (41). Next, (41) oxidized (40) to the allyl cation (42) and was reduced to Fe(I) complex... 

An interesting application of the Fujiwara-Moritani/oxidative Heck reaction for the synthesis of benzo furans was recently reported by the Stoltz lab [31]. A variety of allyl phenyl ethers (all containing electron-rich aryl components) react with 10 mol% palladium acetate, 20 mol% ethyl nicotinate, 20 mol% sodium acetate, and one equivalent of benzoquinone at 100°C to provide benzofurans in 52-79% yield (e.g. 16—>17). The mechanism of this transformation begins with arene palladation of Pd(II) followed by olefin insertion, p-hydrogen elimination, and olefin isomerization to the thermodynamically favored benzofuran product. The resulting Pd(0) species is then oxidized to Pd(ll) thus regenerating the active catalyst. 

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