Bridge flipping and rearrangement of norbornadienyl and 7-methylnorbornadienyl cations

Carbocation

“…The observation of a considerable barrier, possibly greater than 19.6 kcal/mole (Brookhart 1967) in the parent molecule, has led to the consideration that sub stantial laticyclic (Goldstein and Hoffmann, 1971) stabilization may be opera tive, e.g., 228. The barrier to bridge flipping in 233 (R = CH 3 ), the dicyclopropyl analog of 226, has recently been shown to be 13.0 kcal/mole (Coates and Fretz, 1975) and is very similar to that reported for the methyl derivative of the 7-norbornadienyl cation (226) (R = CH 3 ), 12.6 kcal/mole (Brookhart et al, 1967). Apparently, the electronic requirements of the cationic center are satisfied by the pericyclic interaction alone to such an extent that additional derealization of charge by involvement of other more remote π linkages does not lead to appreciable extra stabilization.…”

Perturbational molecular orbital (PMO) theory of homoaromaticity

“…A 1,2-homoconjugate linkage leads to the smallest energy change for this system (28), and it is evident that even for a substantial value of ß (reduction in the homoconjugate resonance integral), the gain in -ir-electron energy will not be too severe. The system is probably best described as a perturbed [1 ljannulenium cation (rather than a perturbed benzotropenylium cation).49 Thus in this case it would be preferable to use the usual PMO approach6 and starting with the aromatic monocycle consider the effect of a 1,6transannular interaction.…”

Lithiation of N,N-dimethylmethallylamine

“…The acidic aqueous layers were basified with 2 N NaOH and extracted with methylene chloride (2 X 50 mL). The combined methylene chloride layers were dried (Na2S04) and evaporated in vacuo to give 3 as an oil; NMR (CDClg) 2.04 (s, 6 H), 2.76 (s, 2 ), 3.17 (s, 2 ), 4.81 (s, 2 ), 7.09-7.60 (m, 10 H), 7.68 (br, 1 H, ex). A solution of this oil in acetone was treated with 1 equiv of HC1 to give 3.40 g (86%) of 3 as the hydrochloride salt: mp 199-201 °C; IR (Nujol) 3290, 2610,1635,1590,1040,950,925 cm'1; mass spectrum, m/e 282-280 ( ± 1).…”

“…Caled for C15H23N0-HC1: C, 66.77; H, 8.97; N, 5.19. Found: C, 66.62; H, 9.24; N, 5.16. 4-(Dimethylamino)-3-methyl-l-phenyl-2-buten-l-one (7). The allylic anion 2 (25 mmol) prepared as described above was cooled to -70 °C and a solution of 1.86 g (12.5 mmol) of N,Ndimethylbenzamide in 5 mL of dry THF was added in one portion by syringe.…”

“…The filtrate was dried with anhydrous magnesium sulfate and concentrated at reduced pressure to afford 18.5 g of 5 as a yellow oil containing a small amount of suspended salts. This material could not be distilled without vigorous decomposition and was (7) Havbrandt, O.; Osterman-Golkar, S.; Wachtmeister, C. A. Acta Chem. Scand.…”