Acid-catalysed hydration of 3-substituted nortricyclanes

Abstract

Disappearance rates of several 3-X-substituted nortricyclanes [X = H, CH₂OH, CH₂Cl, Ac, OH, (CH₃)OH, OAc, CN, NO₂, and oxo] were measured in aqueous perchloric acid by g.l.c. According to activation parameters, solvent deuterium isotope effects, and log k₁versus H_o and log k₁, versusσ_l^q correlations, the hydration mechanism is in most cases A–S_E2 (or Ad_E2), i.e., protonation of the cyclopropane ring is the rate-determining stage of the reaction. The mechanism is different in the case of 3-methyl-3-hydroxynortricyclane (A-1) and 3-acetoxy- and 3-oxo-nortricyclane (A-2). The slope of the linear log k₁versusσ_l^q correlation (–1.30 in 1 mol dm^–3 HClO₄ at 348.2 K) is between those measured for separate protonations of two olefinic carbons of 5-X-substituted norbornenes. The contradiction between the normal inductive effects of the 3-X-substituents and the weak effects of the methyl groups at the cyclopropane carbons can be rationalized by formation of an edge-protonated nortricyclane in the rate-determining stage of the reaction.