Nucleophilic Reactivities of Azulene and Fulvenes

The kinetics of the reactions of azulene (1), 6,6-dimethylfulvene (2), 6-[4-(dimethylamino)phenyl]fulvene (3) and 6(julolidin-9-yl)fulvene (4) with a set of benzhydrylium ions (reference electrophiles) have been investigated in MeCN. The second-order rate constants for these reactions correlate linearly with the electrophilicity parameters (E) of the benzhydrylium ions. According to the linear free-enthalpy relationship log k(2)(20 degrees C) = s(N + E), the nucleophilicity parameters N and s of the pi-nucleophiles 1-4 were determined and compared with those of other types of nucleophiles, Azulene (1, N = 6.66) is about 10 times more nucleophilic than N-methylpyrrole and comparable to 2-methylindole. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)