Polar Effects in the Solvolysis of 4‐Substituted Bicyclo [2.2.2]octyl p‐Nitrobenzenesulfonates. Polar effects. VII

Abstract

SummaryHydrolysisofbicyclo[2.2.2]octylp-nitrobenzenesulfonate (14a,X =p-N02C6H4S03), and nineteen 4-R-substituted derivatives 14b-14 t in 70% aqueous dioxane yield the corresponding bicyclo [2.2.2]octanols 14 (X = OH), exclusively. The 7-center fragmentation to 1,4-dimethylidene-cyclohexane (15) is not observed. The logarithms of most of the rate constants, measured in 80% ethanol, correlate well with the corresponding inductive substituent constants a? of R. Hence, in these cases ionization rate is controlled by the inductive effect of R only. Poor correlations result when the substituents are potentially electrofugal groups, such as COO-, CH,OH, CH,NH,, CONH, and H, the deviations from the inductive regression line corresponding to rate enhancements of 1.6 to 8. These exalted substituent effects are tentatively ascribed to extended hyperconjugation involving two a-bonds. This study corroborates previous evidence that the inductive effect alone does not fully account for the polar effect of some substituents in reactions involving carbocations.In a recent paper in this series [l] a new experimental method for the determination of inductive substituent constants a? was introduced. This method, which is based on the measurement of the pK, of quinuclidinium perchlorate (1, R = H), and of numerous 4-substituted derivatives l), avoids the disadvantages inherent in previous ones [ 11.When applied to studies of substituent effects in nucleophilic substitution reactions a? values correlated well with the logarithms of observed rate constants for bimolecular substitution (SN2) [3] but not for some solvolysis reactions proceeding by way of carbeniumions [4] [5], as in the solvolysis of 1-R-substituted 3-bromoadamantanes (2a) in 80% ethanol. In fact, in the latter case three kinds of substituent effects were discerned: a) When R was hydrogen and alkyl or an electron-withdrawing (-I) substituent, such as BrCH,, COOH, Br or CN, the logarithms of the first order rate constants (logk) correlated very well with the respective 07 values. In these cases, then, ionization to adamantyl cations 3, the precursors of adamantanols 2b and ethyl ethers 2c, is controlled by the inductive effect of R alone; I)In a further paper these a? values are reexamined and revised where necessary [2].

Polar Effects. Part 14. Inductive Charge Dispersal in Bicyclo[2.2.2]oct‐1‐yl Cations

“…The rate constants in 80% EtOH for twenty 4-substituted nisylates 12 were reported previously [9]. Whereas most of them correlated well with the respective a; values, those obtained with nisylates containing a potentially electrofugal substituent4) at C(4), such as CH,OH, CH,NH,, CONH,, COOas well as hydrogen, gave rise to rate enhancements by factors of 2 to 8 based on 0 ; values.…”

“…68 (1985) A few electrofugal substituents (CH,OH, CONH,) were included in the present study in order to determine their effect in the 2-and 3-position of 10 and 11, respectively. The preparation of the nisylates by standard methods and their hydrolyses are [9] [13] or will be published [14] elsewhere.…”

“…When 5. ~O-*M solutions of the nisylates were hydrolyzed in 70 % dioxane, the corresponding bicyclo[2.2.2]octan-1-01s were formed exclusively[9] [13] [14], i.e. no rearrangements or hydride shifts were observed.…”

Basicity of the carbonyl group. Part 13. 4-Substituted camphors as models for transmission of polar effects. A calorimetric, infra-red and 1H NMR study

“…For the remaining compounds the chemical shifts of the C(3) methylene protons are given by eqns. ( 4) and (5) No satisfactory correlation exists for the chemical shifts of the protons C(8)H3 and C(9)H,. Here the effectively constant A6 values of 0.10-0.14 ppm for most of the substituents are significantly less than for those with anisotropic character i.e.…”

A short stereoselective synthesis of the alkaloid vincamine

“…The two compounds as a mixture were deprotonated at -70 °C with LDA-HMPA complex9 (2.2 equiv) and alkylated at the same temperature with ethyl iodide (1 equiv). This led to the anticipated indolo- (6) Langlois, Y.; Pouilhés, A.; Génin, D.; Andriamialisoa, R. Z.; Langlois, N. Tetrahedron 1983, 39, 3755. (7) Andriamialisoa, R. Z.; Langlois, N.; Langlois, Y. J. Org.…”