Nucleophilic substitution reactions of trans-4-(para-substituted phenoxy)-3-buten-2-ones

Reactions of trans-4-(para-substituted phenoxy)-3-buten-2 ones (1-6) with primary amines to give 4-alkylamino-3-buten-2-ones in water are characterized by (1) rates which are first order in amine and 1-6, (2) a Hammett type rho* = 0.11 for reactions of 1-6 with aminoethanol, (3) ..beta../sub nuc/ = 0.37 for reactions of 4-(p-anisoxy)-3-buten-2-one (1) with ethyl glycinate, trifluoroethylamine, 2-ethoxyethylamine, 2-aminoethanol, and n-butylamine, (4) a deuterium solvent kinetic isotope effect k/sub 2/(H/sub 2/O)/k/sub 2/(D/sub 2/O) = 0.98 for reaction of 1 with 2-aminoethanol, and (5) a Ritchie N/sup +/ coefficient of 1 +- 0.2 for reactions of 1 with imidazole, ethyl glycinate, n-butylamine, and hydroxide ion. Reactions of thiols with the title compounds give 4-alkyl-thio-3-buten-2-ones at low concentrations of thiol and 4,4-dialkylthiobutan-2-ones at high concentrations of thiols. The former reactions are characterized by (1) rates which are first order in thiolate anion and 1-6 and (2) rho* = 0.14 for reactions of 1,4-(p-chlorophenoxy)-3-buten-2-one (4), and 4-(p-nitrophenoxy)-3-buten-2-one (6) with N-acetylcysteine. These data support an addition-elimination reaction with nucleophilic attack rate determining. The kinetics of the reactions of 1 and 4 with morpholine and N-methylaminoethanol appear to provide evidence for the partitioning of the putative 1- and 4-amine addend between 1 and 4 and products. 2 figures, 3 tables.