Nortricyclyl system

The nortricyclyl system 69 has been of interest for many years because even though it is formally a 2-bicyclo[3.1.0]hexyl derivative, it has a surprisingly low reactivity. This... 

Diaz and coworkers have investigated the solvolysis of a related system 70 in which, however, the 3,6-methano bridge of the nortricyclyl system is replaced by a 3,6-etheno bridge. Relative rates are given for hydrolysis in 80 % aqueous acetone at 100 °C. Products... 

There has now been a number of reports of the rearrangement of the norbornadiene a adduct to the nortricyclyl system first reported by Coulsen (43). Thus Maitlis et al. (239) found that their phenylpalladation adduct in the presence of pyridine rearranged to this adduct [Eq. (195)]. 

However, the reaction could also occur by attack of coordinated phenyl on a small amount of the norbornadiene tt complex which could be in equilibrium with the nortricyclyl system by the route outlined in Eq. (195). 

CT-participation and hyperconjugation. The great variation in nuclear motion depends on the systems. With 3-nortricyclyl ions Olah has proved the nonvertical stabilization to be more significant than the vertical hyperconjugation this is deary seen from the NMR spectra... 

Other Systems.— The addition of formic, acetic, and chloroacetic acids to quadri-cyclane at 20 °C affords the corresponding esters of exo-2-norbornenol and nortri-cyclenol. Solvent effects and the results obtained using the 0-deuteriated carboxylic acids are interpreted in terms of the six-centre addition mechanism (97) the minor pathway to nortricyclyl products, in the absence of added mineral acid, is the result of leakage from (97) to the norbornenyl cation. ... 

The products of the buffered acetolysis of 2-deuterio-eiido-norborn-5-en-2-yl p-bromobenzenesulphonate (91) have been analysed by mass spectrometric, C and H n.m.r. procedures, and the results discussed in a clearly written and interesting paper. The deuterium initially on C-2 had migrated partially on to C-1 (30%) in the deuteriated cxo-norborn-5-en-2-yl acetates so formed, and was equally and uniquely distributed between C-1 and C-6 of the deuteriated nortricyclyl acetate, the major solvolysis product. Within the limits of detection products derived from C( 1 -> 7) migration or from fragmentation were not formed. The results are consistent with the formation of the symmetrical nortricyclyl cation (92), or ion pair, from the norborn-5-en-2-yl cation, the isomerization being competitive with the reaction of these intermediates with solvent [n.b. C-1 and C-6 in (92) are equivalent positions that correspond to the C-1 and C-2 positions in the norbomenyl system]. 

Nortricyclyl and Quadricyclyl Systems.—The studies of the kinetics of acid-catalysed hydration of exo- and endo-norbornen-2-ols, referred to above, have been extended to include 3-nortricyclanol, 1-methyl-cis- and -rra s-3-nortricyclanols, and 3-methyl-3-nortricyclanol. Solvent deuterium-isotope effects are interpreted in favour of an A-S 2 hydration of the three-membered carbon ring of the secondary alcohols, or an A-1 mechanism for the tertiary alcohol in which case the rate-determining step is the formation of a carbocation (probably the 3-methyl-3-nortricyclyl cation) by elimination of water. 

From a consideration of molecular geometries, the 7-norbornyl system (119) is regarded as a better model for 3-nortricyclyl (120) than is 2-norbomyl p-nitrobenzo-ate. A comparison firstly of the ratio of the rates of solvolysis of (120) and (119), where major relative rate enhancements occur with increasing electron demand by the aromatic ring, and secondly of the values so obtained with those for (96) and (97), has led to the conclusion that the stabilization of cyclopropylcarbinyl is not the result of a-bridging. Thus, for example, the rigidity of the 3-nortricyclyl cation forces... 

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