Nucleophilicity, ambident elimination

Rawal s group developed an intramolecular aryl Heck cyclization method to synthesize benzofurans, indoles, and benzopyrans [83], The rate of cyclization was significantly accelerated in the presence of bases, presumably because the phenolate anion formed under the reaction conditions was much more reactive as a soft nucleophile than phenol. In the presence of a catalytic amount of Herrmann s dimeric palladacyclic catalyst (101) [84], and 3 equivalents of CS2CO3 in DMA, vinyl iodide 100 was transformed into ortho and para benzofuran 102 and 103. In the mechanism proposed by Rawal, oxidative addition of phenolate 104 to Pd(0) is followed by nucleophilic attack of the ambident phenolate anion on o-palladium intermediate 105 to afford aryl-vinyl palladium species 106 after rearomatization of the presumed cyclohexadienone intermediate. Reductive elimination of palladium followed by isomerization of the exocyclic double bond furnishes 102. 

Freitas and O Hair133 studied the gas-phase reactivity of aniline and other nucleophiles toward the methoxymethyl cation, CH3 — 0+=CH2, an ambident electrophile, using flowing afterglow mass spectrometry. For aniline, two reaction channels were observed addition followed by elimination of methanol with concomitant [M + CH]+ ion formation and adduct formation, viz. [M + CH3OCH2]+. 

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