.pi.-Facial stereoselectivity: rates and stereoselectivities of cycloadditions of hexachlorocyclopentadiene to 7-substituted norbornadienes and photoelectron spectral and molecular orbital computation investigations of norbornadienes

Ring strain energies: substituted rings, norbornanes, norbornenes and norbornadienes

“…Electron-withdrawing groups at the 7-carbon in norbornadiene and norbornene decrease the electron density in the anti-p bond. 25 The electron deficient p bond leads to a slower rate of reaction. Electron-donating groups in the 7-position are associated with a faster relative rate of reaction.…”

19F and13C NMR Study of Some Norborn-7-yl Fluoride Derivatives

“…Notwithstanding this apparent anomaly, model system studies have shown that the shift response to such electronic perturbations appears to be ~ystematic.~*'~*'* Second, it has long been known that the introduction of one and two double bonds into the norbornyl skeletal framework leads to significant deshielding (downfield carbon shifts) at the C-7 position (10.15 and 36.78 ppm, respectively; see footnote d to Table 4). '59'9-21 Although this has been ascribed to electron delocalization e f f e~t s , "~~'~ it is now more likely to be recognized as a response to significant structural changes at C-7 (decrease of the LC-1-C-7-C- 4 bond angle and increase in the C-1 (or C-4FC-7 bond length; see Table 2) which lead to a major redistribution of the s and p character in the binding hybrid orbitals." It is pertinent to note that the observed shifts for norbornadiene are successfully mirrored by the IGLO (individual gauge for localized orbitals)-calculated carbon shifts.23 Thus, the fact that electron correlationz4 does not appear to play a major role in describing the chemical shifts of this system tends to confirm the unimportance of electron delocalization phenomena as the origin of the significant deshielding of carbon at C-7.…”

Versatile Catalytic Reactions of Norbornadiene Derivatives with Alkynes

“…Palladacycles (Figure ) have been found to be effective catalysts for the addition/condensation of alkynes with norbornadiene and its derivatives . For the very first time, Tenaglia and co‐workers reported the palladium‐catalyzed addition reaction of terminal alkynes 7 to one of the double bonds of norbornadiene (NBD) 8 under mild reaction conditions .…”

“…Another interesting finding is the recovery of 60% of the loaded catalyst along with the quantitative formation of exo ‐2‐alkynyl‐5‐norbornenes when the reaction was carried out without a solvent with 2.5 mol% phosphapalladacycle and a 10‐fold molar excess of NBD. Surprisingly, norbornene failed to undergo hydroalkynylation under these reaction conditions, suggesting the requirement of a through‐space interaction between the two double bonds of norbornadiene for the coupling to take place . The catalytic system worked well for aza‐/oxabenzonorbornadienes 14 , which also gave the desired products in good yields [Eq.…”