40488-88-8Relevant academic research and scientific papers
Rearrangements of Pentacyclododecyl Cations
Kirmse, Wolfgang,Ritzer, Joachim
, p. 4965 - 4986 (2007/10/02)
Pentacyclododecyl cations (29-32) have been investigated as models for distorted 2-norbornyl cations.When 30 and 32 were generated by solvolysis (brosylates 8 and 20) or by nitrous acid deamination (amines 10 and 21), Wagner-Meerwein rearrangement occured competitively with solvent capture.Both epimeric precursors, 3x and 3n, reacted with high exo-selectivity.In contrast, endo-precursors 2n (12, 13) produced major quantities of endo-products.Retentive displacement at 2n is attributed to intervention of the bridged ion 29, generated independently by protonation of the hexacyclododecane 28.A rapid, degenerate alkyl shift in 30 was detected by means of a deuterium label (-30 -30).Subsequent rearrangement(-30 --> -32) suggests that the bridged structure 31 is not significantly lower in energy than 30.- Thus, pentacyclododecyl cations show several features uncommon to a norbornyl system: (1) relatively slow Wagner-Meerwein rearrangement, (2) fast endo,endo-3,2-shifts, and (3) abundant formation of 29 (a 7-bridged norbornyl cation), all explicable in terms of the distorted norbornyl geometry. - Less nucleophilic media led to fragmentation of 30 and/or 32.In trifluoroacetic acid the tetracyclododecenyl cation 64 was formed and trapped selectively.The dehydration of 7 on alumina (275 deg C) provided a convenient route to the alkene 17.Minor products (47, 50, 51) arose via competitive fragmentation-elimination paths.
Orbital Interactions. XII. Product Studies and Competition Kinetic Measurements of the Birch Reduction of a Series of Hexahydrodimethanonaphthalenes and their Interpretation in Terms of Orbital Interactions Through Space and Through Bonds
Chau, Diem Dieu,Paddon-Row, Michael N.,Patney, Harish K.
, p. 2423 - 2446 (2007/10/02)
Relative rate constants for the Birch reduction (Li/ liq.NH3/ ButOH) of the three isomeric hexahydrodimethanonaphthalenes (3)-(5) and the octahydro analogues (10)-(13) were obtained and compared with those obtained for the reduction of norbornadiene and norbornene from an earlier study.Diene (5) was reduced almost 2000 times more rapidly than norbornene and 20000 times more rapidly than the monoene (13).Rate-enhancement factors for dienes (3) and (4) were less substantial but meaningful: 19 for (3) and 35 for (4) .These rate enhancements were attributed to the operation of ?* orbital interactions through space in diene (5) and to the presence of ?* orbital interactions through four bonds in dienes (3) and (4).The existence of a linear relationship between the natural logarithm of the rate of reduction of a substrate and its LUMO energy (obtained from either gas-phase electron affinities or ab initio MO calculations) supports this conclusion.The only-fair correlation of the above relationship was attributed to the neglect of other factors, such as the electronic structure and the geometry of the anion radical, which contribute to the overall rate of the Birch reduction.These two factors were explored by using PMO theory and ab initio MO calculations.In particular, full geometry optimizations (UHF, STO-3G basis set) on the anion radicals of norbornadiene (1) (C2v symmetry constraint) and norbornene (22) (Cs symmetry constraint) were carried out, and their geometries reported.Noteworthy is the strong pyramidalization of the olefinic centres of (1) and (22) in the endo direction.These pyramidalizations explain the observed stereoselective exo protonation of the anion radical of (1), and also the much faster rate of reduction of (1) compared with (5), since the pyramidalization im the anion radical of (5) is such to hinder protonation.The geometries of anion radicals appear to have a profound effect on rates, on stereoselectivity of protonation, and on the structures of the final products, and this is discussed in detail.The synthesis of the diene (3) is also described.
Steric Effects on Reaction Rates - III. Application of Force-Field Calculations to Chromic Acid Oxidation of Alcohols
Mueller, Paul,Blanc, Jacky,Lenoir, Dieter
, p. 1212 - 1220 (2007/10/02)
The rates of oxidation with chromic acid of 15 bi- and polycyclic secondary alcohols have been measured and correlated with strain changes calculated by the MM1-program between the alcohols and the corresponding ketones.A correlation of the same quality is obtained upon representation of OH-strain by CH3-strain.The significance of the correlations with respect to the oxidation mechanism as well as the limitations of the applicability of force-field calculations to reactivity problems are discussed.
Steric Effects in endo,exo-Tetracyclo3,6.02,7>dodecanes: Influence of 4-Substituents on the Solvolysis of Epimeric 11-Sulfonates
Lenoir, Dieter,Frank, Robert M.
, p. 3336 - 3348 (2007/10/02)
By stereoselective additions of 11-anti-acetoxy-endo,exo-tetracyclo3,6.02,7>dodec-4-ene (12a) compounds 6, 13 - 18 have been prepared.Olefin 19, obtained by Wittig reaction from 17, was hydrogenated yielding methyl compound 9
