Kinetics of reduction of 1,5-diarylpenta-1,4-dien-3-ones with sodium borohydride in propan-2-ol

Symmetrically disubstituted 1,5-diarylpenta-1,4-dien-3-ones undergo quantitative 1,2-addition with sodium borohydride in propan-2-ol. The rate coefficients for reduction of the para- and meta-substituted compounds correlate with the Hammett equation, yielding a ρ value of 0·913 at 40 °C. The influence of ortho-, meta-, and para-substituents on the rate of reduction are linearly related to the hydrolytic reactivities of the corresponding ethyl trans-cinnamates.