Nucleophilic substitution by piperidine in some 3-halogenocyclohex-2-enones

Abstract

Reactions of 3-chlorocyclohex-2-enone, 3-chloro- and 3-bromo-5,5-dimethylcyclohex-2-enone, and 3-chloro-2-methylcyclohex-2-enone with piperidine in ethanol and dimethylformamide were studied kinetically at 30–90 °C. Substitutions are free from side reactions. Solvent effects are rather small. Measured rate coefficients for 3-chloro-cyclohexenone are larger than those of 3-chloro-5,5-dimethylcyclohexenone showing a different degree of coplanarity in the vinyl-carbonyl skeleton. The chloro- and bromo-5,5-dimethylcyclohexenones react at similar rates. Owing to the α-methyl group, rate-coefficient ratios between 3-chloro- and 3-chloro-2-methyl-cyclo-hexenone have values of 2–2·6 × 10².