The competitive scissions of cycloalkane oxiranes by charged and neutral nucleophiles in acidic aqueous methanol

Abstract

. Can. J. Chem. 55,4144 (1977).Six related oxiranes (the cis and trans isomers derived from 3-methoxycyclopentene and from 3-methoxvcvclohexene. as well as the oxiranes from the corresuonding unsubstituted olefins) were each treated under the same conditions with an acidic soiution containing charged and uncharged nucleophiles (chloride ion, water, and methanol). The corresponding perchloric acid catalyzed scissions were also carried out. Accurate and reproducible methods of product analysis for the reaction mixtures were developed. In this way, nucleophilic attacks upon different oxiranes were compared directly. Attacks by different nucleophiles upon the same oxirane, or by a single nucleophile upon different positions of the same oxirane, were compared in the very same solution. The results are considered to provide the most extensive demonstration of the effects of charge orientation yet available. The synthesis of some new isomeric 1,2,3-trisubstituted diols and dimethoxyalcohols are reported. Chem. 55,4144 (1977).Six oxirannes de m&me type (les isomeres cis et trans du mCthoxy-3 cyclopentene et du methoxy-3 cyclohextne, aussi bien que les oxirannes provenant des olefines non-substitukes) sont traitks individuellement dans les mCmes conditions par une solution acide contenant des nucltophiles charges et non-charges (ion chlorure, eau et methanol). On rkalise aussi les scissions correspondantes catalysees par I'acide perchlorique. On met au point des mtthodes d'analyse prkcises et reproductibles des produits provenant du mklange rtactionnel. De cette f a~o n , les attaques nuclkophiles sur les differents oxirannes sont comparees directement. Les attaques de differents nuclkophiles sur le m&me oxiranne, ou par un seul nuclkophile ti diffkrentes positions du mdme oxiranne, sont comparees dans la m&me solution. Les resultats semblent apporter la demonstration la plus marquee connue jusqu'ti maintenant sur les effets d'orientation de charge. On rapporte la synthtse de quelques nouveaux diols trisubstituks-1,2,3 isomtres et de dimethoxyalcools.[Traduit par le journal]The mechanism of oxirane2 opening and the stereo-and regioselectivity of the nucleophilic addition have been topics of great interest (1-8).In these laboratories, we have expended a good deal of effort in this area due to our interest in conformational factors and the interaction of substituents in the cyclopentane and cyclohexane ring systems (see refs. 7-10 and references cited therein). In fact, it was the availability of compounds synthesized during these studies (for 'Present address: Defence Research Establishment Ottawa, Ottawa, Ont., Canada KIA 024.'For the remainder of this paper oxiranes will be designated as epoxides or cycloalkene oxides. These designations have been in use for many decades.example most of 1-19) (see Figs. la and 1b)which allowed us to proceed with the experiments described in this paper.Although several papers deal with the scission of 3-substituted cyclohexene or cyclopentene oxides (see, for example, refs. 7, 8, and 1...