Cyclohexane compounds. VII. Nucleophilic scission of the stereoisomeric 3-methoxycyclohexene oxides

Abstract

The mode of scission of cis- and trans-3-methoxycyclohexene oxides by hydrogen chloride, hydrogen bromide, ammonia, acetic acid, and methanol (under both acidic and alkaline conditions) has been examined using vapor-phase chromatography to detect and isolate minor isomers. Approximately 10% of the product from opening of the trans oxide is formed by attack at position-2 with each of these nucleophiles, whereas opening of the cis oxide proceeds exclusively by attack at position-1. The results are interpreted as reflecting very similar transition states for all of these reactions, with differences in product distributions for the two oxides being governed by the inductive effect of the methoxyl group and by steric factors in the corresponding transition states.

Epoxide ring-opening approach to the synthesis of diverse trisubstituted cyclopentanes

“…27,28 In the case of epoxide 1, bearing methyl group at the nitrogen atom, the inductive effect of the amino moiety at C3 is the controlling factor, and the ring opening mainly goes through transition state 11 to form C1-adducts, regardless of steric hindrance. All the same, the electronic effect of N,Ndibenzyl amino moiety in epoxide 2 does not promote the high level of regioselectivity.…”

Epoxides and trans-chlorohydrins of 3-methoxycyclopentene and their use in conformational studies in the cyclopentane system

“…Less evidence is as yet available in the cyclopentane system, but aside from analogy, the fact that the kinetics of oxide closure show the same anomaly as the product ratio in oxide scission or chloronium ion scission seems to leave no doubt that rate control still applies in the new system. 'This seems a reasonable hypothesis for base-catalyzed scissions, strengthened in the cyclohexane work (8) by the observation that variations in the nucleophile caused little difference in the product ratios. It is of course not obvious that acid-catalyzed scissions have transition states similar geometrically to those for base-catalyzed scission, but the previously recorded observations (8) seem to make it clear that in the cyclohexane series, they do.…”

“…'This seems a reasonable hypothesis for base-catalyzed scissions, strengthened in the cyclohexane work (8) by the observation that variations in the nucleophile caused little difference in the product ratios. It is of course not obvious that acid-catalyzed scissions have transition states similar geometrically to those for base-catalyzed scission, but the previously recorded observations (8) seem to make it clear that in the cyclohexane series, they do. The point has not yet been thoroughly verified in the cyclopentane series, but the regularities mentioned in footnote 6 seem to allow no other interpretation.…”

“…Thus ordinary conformational analysis may be brought to bear to explain both the rates of oxide formation and the product ratios from oxide scission. This has now been done in several series of cyclohexane compounds (8).…”

“…For the past several years we have been interested in forming a reasonably accurate picture of the transition states involved in the formation and scission of the oxirane ring in the stereoisomeric oxides of 3-methoxycyclohexene (1 and 1 2) (1)(2)(3)(4)(5)(6)(7)(8). Our approach has been that the model chosen for the transition state must explain both the relative rates of formation of the oxides from various halohydrins and the product ratios obtained in the scission of the oxides.…”