Nucleophilic Reactivities of Azulene and Fulvenes

Abstract

Abstract 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 °C) = s ( N + E ), the nucleophilicity parameters N and s of the π‐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. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)