Norbornanes. Part 19. The Inductive Model for Norbornyl Cation Formation

Abstract

Two CH, groups at C(6) of 2-exo-(10a) and 2-endo-norbornyl p-toluenesulfonate l l a lower their solvolysis rates in 80% EtOH by factors of 28 and 16, respectively. A spirocyclopropyl group including C(6), as in 21s and 22a. reduces the rate ofexo-and endo-ionization by factors of 250 and 8, respectively. The geminally dimethyl-substituted tosylates 10a and l l a yield the 2-em-alcohol lob, whereas the spirocyclopropyl-substituted tosylates 21a and 22a furnish rearranged 3-brendanol 23. These findings are readily rationalized by the inductive model, according to which norbornyl cation formation is controlled by the inductive effect of dorsal substituents.Substituents at C(4), C(5), C(6), and C(7) of 2-exo-and 2-endo-norbornyl p-toluenesulfonate (tosylate) 1 and 2, respectively, control solvolysis rates by their inductive (I) effect only [ 11. This follows from the observed linear correlation of the logarithms of the rate constant logk with the inductive constants of the substituents CT: [2] at these positions according to the equation log k/ko = ploy, which, in addition to other data [3], precludes steric effects as a significant rate and product-controlling factor'). 7

Nature of the Electronic Factor Governing Diastereofacial Selectivity in Some Reactions of Rigid Saturated Model Substrates

“…This result is significant in view of the continuing debate concerning the relative electrondonating ability of C-C and C-H bonds in saturated systems. 7,16,82 However, it is in line with other observations (NMR and reactivity parameters) from various model polycycloalkane systems (1,4-disubstituted bicyclo[2.2.2]octanes, 48, 83 1,4-disubstituted bicyclo-[2.2.1]heptanes, 63d 1,4-disubstituted cubanes, 84 2,6disubstituted bicyclo[2.2.1]heptanes, 85 1,3-disubstituted adamantanes, 39b,63f,86 1,3-disubstituted bicyclo-[1.1.1]pentanes, 50a 1,5-disubstituted bicyclo[3.1.1]heptanes, 51 1,5-disubstituted trishomobarrelenes, 87 and 5-substituted 2-adamantyl derivatives 5a,49b,63i, 65,88,89 ). Thus, the experimental evidence from rigid polycycloalkanes, the archetypal model substrates for delineating electronic substituent effects, is overwhelmingly in favor of the C-H bond being a better donor than C-C for long-range interactions (γ-and δ-effects) in the neutral ground-state and electron-deficient species.…”

Rearrangements of Spirocyclobutane-Substituted 2-Norbornyl Cations

“…The mixture was stirred for 16 h at room was kept at room temp. for 3 d when 12% of 34a, 13 C NMR temp. The precipitate was recrystallized from methanol to give 63 (CDCl 3 ): δ ϭ 86.315 (33%), 86.363 (67%), and 17% of 39a, 13 …”

“…The sample [25] . pentane solution was washed with water, dried (MgSO 4 ), and concentrated at reduced pressure (100 Torr) to give 0.12 g (87%) for 32, the labeled ketone was converted into 32a, 13 C NMR in methanol (1 ml) were added 24 (40 mg, 0.26 mmol) and saturated (CDCl 3 ): δ ϭ 92.591 (36±1%), 92.638 (64±1%). The NMR solution methanolic HCl (2 drops).…”

“…The degenerate rearrangements of the 2-norbornyl cation [8] have often been used to probe the influence of substituents [8] [9] [10] . Dramatic changes (see below) were induced by cyclopropane rings which were spiroanellated to the 3- [11] [12] , 6- [13] [14] , and 7-positions [11] [12] of the 2-norbornyl system. We now report on analogous spiroanellations of cyclobutane, in order to compare the effects of three-and four-membered rings.…”