Synthesis of norbornene endo-epoxide (3-oxatricyclo [3.2.1.02,4]octane).

Azabrendanes V. Synthesis and reactions of stereoisomeric exo- and endo-5-aminomethylbicyclo[2.2.1]hept-2-ene-based ureas

“…Moreover, in the 13 C NMR spectra of the epoxy derivatives , signals corresponding to nuclei of the epoxy cycle (50-52 ppm) replaced those of the C 2 and C 3 carbon nuclei in the norbornene fragment (136-137 ppm). Accompnaying this is a significant (20-25 ppm) upfield shift in the signal from carbon bridge (C 7 ) [29,30]. Collectively, this data provides strong evidence for formation of epoxides with exo-orientation of the epoxy cycle from ureas with an exo-substituent in the norbornene fragment.…”

“…However, the signals of the H 2 and H 3 protons of the epoxide cycle, in the 2.9-3.1 ppm region of the 1 H NMR spectra, are characteristic of epoxy compounds [23,24,29,30]. Additional, important proof for the epoxide structure was the shift to high field (0.84-0.66 ppm) of the signal of one of the protons (H 7a ) at the bridge carbon atom, a phenomenon caused by the influence of the magnetic field of the threemembered ring.…”

Epoxidation of substituted norbornenes. Stereochemical aspects and accompanying intramolecular transformations

“…In fact, the vast majority of known epoxynorbornanes have exo-configuration in which the protons of the C(7)H 2 bridge are appreciably non-equivalent, one of them being arranged directly The non-equivalence of the bridging protons in the 1 H NMR spectrum as well as the unusual shielding of the C(7) atom in the 13 C NMR spectrum are the two criteria, which can be used to determine the stereochemistry of an epoxynorbornane fragment. 125,128 The exo-configuration has been confirmed by X-ray diffraction analysis. 129,130 exo-Stereoselective epoxidation has also been observed for the 7-oxa analogue of norbornene 131 and for polycyclic compounds, related to norbornene but much more complicated, such as syn-1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanonaphthalene 11 and its derivatives 12 and 13.…”

Electronic control of stereoselectivity. 6. Directionality of singlet oxygen addition to 1,4-dimethoxynaphthalenes laterally fused to bridged bicyclic systems

“…Thermodynamic Considerations. Leaving aside for the moment the electronic considerations just presented, we next turn our attention to MINDO/3 calculations of the heats of formation of [20][21][22][23][24][25] as models for the presumed primary reaction products. According to the results summarized in Table IV, the endo peroxides 21, 22, and 24 should be thermodynamically preferred.…”

“…Certainly, consideration of the thermodynamic stabilities of the assumed primary endo peroxide products does not lead to a satisfactory answer. Perhaps the model systems [21][22][23][24][25][26] are too simple; on the other hand, the singlet oxygen discrimination exhibited by 4 and 5 compares closely to that found for the somewhat less structurally intricate hydrocarbons 1 and 2.1 Furthermore, although endo peroxides of general formula 13 are known to be subject to retrocycloaddition,15 this possibility does not seem to contravene the operation of electronic influences.…”