Quadricyclanes structure

The aim of this part of the study was to incorporate the azido group into the strained quadricyclane structure. The pathways shown in Fig. 2.13 were pursued. 

Figure 2.13 Pathways of incorporating the azido group into the strained quadricyclane structure...

Highly strained hydrocarbons such as quadricyclane (structure see below) may serve as high-performance aviation fuels (Hill etal., 1997). It is, therefore, important to know the environmental behavior of such compounds, particularly with respect to spills. In this context, Hill et al. (1997) have studied the hydrolysis of quadricyclane in aqueous solution at pH values between 3 and 4 as well as in soil slurries exhibiting pH values between 4.6 and 6.4. They found that in homogeneous aqueous solution at a given pH, the disappearance of quadricyclane followed pseudo-first-order kinetics, and that two major products (i.e., nortncyclyl alcohol and exo-5-norbomen-2-ol) were formed at a ratio of about 15 ... 

Doms, L., H. J. Geise, C. Van Alsenoy, L. Van den Enden, and L. Schafer. 1985. The Molecular Orbital Constrained Electron Diffraction (MOCED) Structural Model of Quadricyclane Determined by Electron Diffraction Combined with Ab Initio Calculations of Potential and Geometrical Parameters. J. Mol. Struct. 129, 299-314. 

Quadricyclane is a strained molecule which is relatively easy to synthesize. The strain energies of related structures are presented in Fig. 2.12. 

Norbornenes substituted at C-5 and/or C-6 give the [2 + 2] cycloadducts with 4-methyl-3//-l,2,4-triazole-3.5(4//)-dionc, but with low yields27. Rigorous structural proof was secured by chemical transformation of the 1,2,4-triazolidine 4, derived from 5-c.vo-phenylthionorbornene, to the same norbornadienediazetidine derivative 5 as is formed from quadricyclane. Cleavage of the 1,2,4-triazolidinedione ring in the adduct 5 was conveniently accomplished by hydrazinolysis. 

The nucleophilic addition of methanol to quadricyclane radical cation, 90 ", produced two methanol adducts, 102, having a 3-ejco-methoxy group, and 103, bearing a 7-fl h -methoxy group. The stereochemistry of the methoxy groups in these structures identified the direction of nucleophilic attack upon 90 + as exclusively from the exo position [242], It can be viewed as a backside attack of the nucleophile on the weakened cyclopropane bond with inversion of configuration. 7-Methylenequadricyclane also was attacked exclusively from the exo face [243]. 

Quadricyclanes (160) also undergo a valence isomerization to norborna-dienes if irradiated in the presence of electron acceptors such as fumaro-nitrile (Jones and Becker, 1982). Two distinct radical cation structures are observed for the hydrocarbon, corresponding roughly to the bonding patterns of norbornadiene and quadricylane, respectively (Roth et al., 1981). 

Difiuorocarbene underwent addition to quadricyclane to give enr/u-6-(2,2-difluorovinyl)bi-cyclo[3.1.0]hex-2-ene together with three other products in 3% yield.The proposed formation of an insertion product into one of the cyclopropane C — C bonds was not verified in this reaction, but was observed in the reaction with other carbenes such as dichlorocarbene and bis(methoxycarbonyl)carbene. The major product with these carbenes possessed a bi-cyclo[3.2.1]octa-2,6-diene structure as the result of the insertion of the carbene into the cyclopropane bond next to the methylene bridge. ... 

As an even more valuable asset for mechanistic investigations, any structural changes during product formation can be unravelled by analysing where in the product the labels show up. Figure 20 provides a nontrivial example. In the photoreaction of benzoquinone with quadricyclane, the polarizations arise from fhe 1,5-biradical BRi. The singlet exit channel leads to the oxolane Pi, the triplet channel to the oxetane P2. The structure of the quadricyclane-derived moiety in BRi is identical to that in Pi but quite different from that in P2, so obviously Pi is formed by a simple combination of the radical centres whereas an extensive skeleton... 

Sprague, 1972, 1973) was completed, refined structures for phen-anthrene (Kay et al., 1971) and quadricyclane (J. C. Speakman and A. Kerr, private communication) became available, and the agreement between the calculations and experiment is now quite good. The errors appear to have been in the original experimental values, not in the calculations. 

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