Acid-catalyzed hydrolysis of bridged bi- and tricyclic compounds. XXXVII. Kinetics and mechanisms of 1- and 3-acetoxynortricyclanes

Abstract

The disappearance of 3-and 1-acetoxynortricyclanes (1 and 2) in aqueous perchloric acid was followed by capillary gas chromatography at different temperatures and acid concentrations. According to the activation parameters, solvent deuterium isotope effects and parameters of excess acidity equations, the A AC 2 ester hydrolysis with two water molecules in the transition state is dominant at the lower acid concentrations studied (1-5.5 M HClO 4 ) and the Ad E 2 hydration of the cyclopropane ring is dominant at higher acid concentrations (6-8 M HClO 4 ) at 298 K. 3-Nortricyclanol (3) is formed via hydrolysis from 1, whose hydration products were not analyzed. 2-Norbornanone (4) is formed via both hydrolysis and hydration from 2.

Acid‐catalyzed hydrolysis of bridged bi‐ and tricyclic compounds. XXXVIII—Kinetics and mechanisms of 1‐ and 3‐nortricyclanols

“…The disappearance of the substrates in aqueous perchloric acid was followed by GC (with a FFAP capillary column) using cyclohexanone (for 1-OH) or 2-norbornanone (3, for 2-OH) as the internal standard and dichloromethane as the extraction solvent. 1 The pseudo-first-order rate constants were obtained from the slopes of the strictly linear (r = 0.9990-0.999 97) correlation of ln S t vs t(S ? = 0), where S t is the ratio of the GC integrals of the substrate and the internal standard at time t. Each rate constant was measured twice, the values being equal to within at least 4% (average 1.4%) for both 1-OH and 2-OH.…”

“…Recently, a mutual comparison of the kinetics and mechanisms of acid-catalyzed hydrolysis (hydration) of 1-and 3-X-substituted nortricyclanes or tricyclo[2.2,1.0 2,6 ]heptanes (1-X and 2-X) was started at our laboratory. 1 In the first case, when X = OAc, the disappearance rates and reaction mechanisms of the isomers were very similar, although the reaction was changed from A AC 2 ester hydrolysis 2 to the Ad E 2 or A-S E 2 hydration of the cyclopropane ring 3 with increasing acid concentration. Even the concentration [c(HClO 4 ) % 6 mol dm À3 ] where the portions of the two reactions were equal was observed to be similar for both isomers.…”

“…1-OH is much more reactive than 2-OH (990 times in 1.0 M HClO 4 at 298.2 K) and also clearly more reactive than 1-acetoxynortricyclane (1-OAc; 19 times). 1 Hence it is natural that 1-OH could not be detected by GC in the hydrolysis of 1-OAc. The rate constants measured for 2-OH are in fair agreement with those measured earlier under similar conditions.…”

“…Even the concentration [c(HClO 4 ) % 6 mol dm À3 ] where the portions of the two reactions were equal was observed to be similar for both isomers. 1 This similarity is surprising, because 1-OAc is a tertiary and 2-OAc a secondary acetate. Evidently, the location of the acetoxyl group at a cyclopropane carbon in the tertiary isomer makes the normal A AL 1 ester hydrolysis in this case less probable.…”

“…2 1-Nortricyclanol (1-OH) was considered to be a possible unstable intermediate product of the hydrolysis for 1-OAc. 1,4 Therefore, it was chosen as the subject of additional studies on the comparison of 1-and 3-substituted nortricyclanes, when accordingly 3-nortricyclanol (2-OH) is the other isomer. Their disappearance rates were measured in aqueous perchloric acid at different temperatures and acid concentrations and in deuterioperchloric acid, and the products were analyzed in order to elucidate the reaction mechanisms.…”