Quadricyclane, preparation

Ni° means nickel prepared in situ by reduction of nickel salts, or a Ni° complex containing easily displaceable ligands. 6 Disiamvlborane. Quadricyclane can be employed in place of dicyclopentadiene with which it is in equilibrium. 

Quadricyclane may be prepared by direct irradiation of bi-cyclop.2. l]hepta-2,5-diene3 and 2,3-diazatetracyclo[4. 3.0.0.4 8-07,9]non-2-ene6 or by photosensitized isomerization of bicyclo-... 

A unique example is the production of a polymer that contains Cgo- The fuller-ene monomer was prepared by cycloaddition of quadricyclane followed by polymerization in norbomene at room temperature.235 The product has cis trans ratios between 3 1 and 6 1 depending on the concentration of the monomer. A processable film containing 1% C60 exhibits electronic and electrochemical properties that are typical of the carbon cluster. 

The opposite substrate-induced diastereoselectivity is observed in the cycloadditions to norbor-nenc and norbornadiene, since the adducts exo-9 and endo-10 are obtained, respectively6. The e.w-adduct 10, prepared from norbornene, can also be obtained, together with a rearrangement product, by cycloaddition to quadricyclane followed by double-bond hydrogenation8. 

Photoisomcrization of bicyclo[2.2.1jhepta-2,5-diene (I) in the presence of acetophenone as sensitizer provides a method for the preparation of quadricyclane (2). The... 

Quadricyclane may be prepared by direct irradiation of bi-cyclo[2.2.l]hepta-2,5-diene and 2,3-diazatetracyclo[4.3.0.0. -0 ]non-2-ene or by photosensitized isomerization of bicyclo-[2.2.1]hepta-2,5-diene. Several substituted quadricyclanes have been prepared by direct irradiation and by photosensitization. The procedure described above can be used to isomerize substituted bicycloheptadienes to the corresponding quadricyclanes when traces of sensitizers can be conveniently removed or their presence does not interfere with further use of the quadricyclane. 

Quadricyclane in Csl or KBr matrices, prepared by deposition in the salt under conditions that yield single-molecule isolation, is rapidly converted into norbornadiene under conditions that induce color center formation in the alkali halide rapid-growth vapor deposition, or UV or X-ray irradiation. The reaction proceeds only at temperatures at which color centers of the missing electron type (H center) are mobile. At lower temperatures (T < 90 K), UV irradiation of norbornadiene converts it into quadricyclane in the usual fashion (Kirkor et al., 1990). 

Of the photochemical conversions of 3,6-bridged cyclohexa-1,4-dienes to 3,6-bridged syn-tricyclo[3.1.0.0 ]hexanes, the light-induced isomerization of norbornadienes to quadricyclanes (see Houben-Weyl, Vol.4/5a, pp 232-237) has been most intensively studied. The parent hydrocarbon, quadricyclane (1, tetracyclo[3.2.0.0 . 0 ]heptane) has become available on a preparative scale by acetophenone sensitized isomerization of norbornadiene (bicyclo [2.2.1]hepta-2,5-diene). ... 

Obviously, substitution of the norbornadiene double bond with two electron-withdrawing groups lowers the activation energy barrier for valence isomerization even more. A summary of examples for the preparation of 1,5-disubstituted quadricyclanes 4 is given."... 

Almost exclusive intercyclic [(2cr + 2a) + 2n cycloaddition was observed in substrate 10 (prepared from the bis-quadricyclane isomer of the j9-lactam by [(2cr-l-2ff)-l-27t] addition with dimethyl butynedioate). ... 

Both the acid induced and the photochemical rearrangement of the norbornaidiene derivative (146) affords the hydroxynaphthalene (147). The photo-process is not affected by triethylamine and it is thought to involve benzy lie-ally lie C-O bond cleavage. No evidence was put forward for the intermediacy of a quadricyclane. Prinzbach smd his coworkers have reported the synthesis of the oxanorbornadienes (148) and their photoconversion into the corresponding oxaquadricyclane derivatives (149) on irradiation. The azaquadricyclanes (150) have been prepared by the irradiation of the corresponding norbornadiene derivatives (151). ... 

Five batches of sulfonamide-linked (3a) and two batches of carboxamide-linked (3b) polystyrene-anchored Co (II) tetra-arylporphyrin catalysts were prepared with cobalt contents ranging from 0.28 to 0.48%. The standard activities with O.IM quadricyclane in benzene were measured for each batch (Table I). The pseudo first-order rate constants for disappearance of quadricyclane were obtained with O.I g of catalyst in 10 mL of solvent. These rates were normalized to standard activity conditions of 1.0 g/L ky, in Table I) and to an activity based on metal content ( m in Table I). 

These observations suggested that Pd (II) chloride bound to phosphine-substituted polystyrene might be an eflFective catalyst for the conversion of quadricyclane to norbornadiene. We therefore investigated the preparation of such a polymer-anchored phosphine Pd (II) chloride catalyst. 

Toda and co-workers have published a full paper on the preparation of the benzo-l,2 4,5-dicyclobutadiene (141), and have described some more of its reactions. Addition of diphenylcyclopropenone in refluxing xylene gave the novel quadricyclane derivative (142), which rearranged on further heating. Reaction of (141) with tetra-cyanoethylene resulted in an olefin metathesis reaction with one of the cyclobutadiene double bonds to give (143), but with dimethyl maleate, ° addition took place... 

Dimethylenecyclobutene has been prepared by thermolysis of 1,4-dimethylene-tricyclo[4,2,l,0 ]nonene (151), which is itself available from the addition product of quadricyclane and maleic anhydride. The benzocyclobutene analogues of (151) do not decompose thermally to give benzocyclobutadiene. Both exo- and endo-epimers (152) and (153) give (154), the product of intramolecular [2 + 2] addition. Under the same conditions, saturated e do-benzocyclobutene (155) rearranges to its exo-isomer (157). 

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