Quadricyclane

Submitted by Claiboltune D. Smith Checked by A. J. Tagoi and J. Meinwald 

A source of nitrogen is attached to the top of the condenser to protect the system from oxygen. The condenser serves as a safeguard in case the temperature of the S3 stem exceeds the boiling point of the solvent. 

Bicyclo[2.2. l]hepta-2,5-diene was obtained from Shell 

Chemical Company and can be used as supplied. However, if the diene is distilled it should be used at once. The uninhibited diene may form a white, insoluble polymer or peroxide if allowed to stand in the presence of air and light. The use of undistilled diene results in a slightly lower yield of quadricy-clane. The checkers used bicyclo[2.2.1]hepta-2,5-diene supplied by the Aldrich Chemical Company, Inc. This was distilled prior to use to give a pure sample, b.p. 89-90.5°, 1.4680. 

Lower wattage lamps can be used, although the irradiation time would be somewhat longer. The checkers found this reaction to be almost complete in about half this time lamp age and other similar factors will cause appreciable variation in the irradiation time required. 

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The skeletal rearrangement of various strained cyclic compounds is carried out with a catalytic amount of soluble complexes of PdCl2. Namely, the rearrangements of bulvalene (67) to bicyclo[4.2.2]deca-2,4,7,9-tetraene (68)[54], cubane (69) to cuneane (70)[55], hexamethyl Dewar benzene (71) to hexa-methylbenzene (72)[56], and 3-oxaquadricyclanes[57] and quadricyclane (73) to norbornadiene[58-60] take place mostly at room temperature. Reaction of iodocubane (74) with a terminal alkyne catalyzed by Pd(0) and CuBr unexpectedly affords an alkynylcyclooctatetraene 75, without giving the desired cubylalkyne 76. Probably the rearrangement is a Pd-catalyzed reaction[61]. 

When additional substituents are introduced in the 2- and/or 4-position, the thermal rearrangement gives products in which the substituents that were originally located in the 1- and 5-position of the quadricyclane are then located at C4 and C5 of the oxepin 7.30,123 In order to trap intermediates of this rearrangement reaction by intramolecular cycloaddition vinyl and acetylene groups were linked with different spacer groups to C2 of quadricyclane.123 In this manner two different intramolecular cycloadducts were isolated in addition to oxepin derivatives.123... 

In 15-58, we used the principle of conservation of orbital symmetry to explain why certain reactions take place readily and others do not. The orbital symmetry principle can also explain why certain molecules are stable though highly strained. For example, quadricyclane and hexamethylprismane are thermodynamically much less stable (because much more strained) than their corresponding isomeric dienes, norbomadiene and hexamethylbicyclo[2.2.0]hexadiene (108). Yet the... 

Of the many reactions that have been performed with heteroolefinic systems we mention the addition to 1,3,5-triphosphabenzene, because of the special relationship between the 1,4-adduct 50 and the corresponding quadricyclane 51 [90]. 

There are several known examples of silenes participating in [2 + 2 + 2] cycloadditions, including reactions with norbornadiene and with quadricyclane. Examples of these reactions with norbornadiene are shown in Eq. (30), where the silene bridges the 2,6-positions.38 5, 53 ,7U85 ,88 This reaction has only been investigated using some of the Auner-type silenes. In many cases mixtures of stereoisomers were obtained, and in some cases products of an ene reaction were also observed. 

The reactions with quadricyclane, shown in Eq. (31), gave products identical to those formed by the same silene reacting in a [2 + 2] manner with norbornene. Mixtures of exo endo isomers were frequently observed. Again, only silenes of the Auner type have been studied with this reagent,51-53,185,188 so it is not known whether the Wiberg- or Brook-type silenes will undergo this mode of cycloaddition. 

Kaupp and Prinzbach have shown that the sum of the quantum yields for the forward and reverse transformations of a number of norbornadienes and quadricyclanes is about unity(115 117) ... 

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. 

The reaction of quadricyclane with hexafluoroacetone azine 290 under similar conditions affords a mixture of a 1 1 adduct 298, the o , -bis-cycloadduct 299 formed by reaction of the C=N bond in 298 with quadricyclane, and the criss-cross addition product 300 (Scheme 41) <1995JFC(72)147>. 

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. 

Molecule 2 is of considerable theoretical interest.24 At the time of our success in generating 2 by flash pyrolysis of quadricyclane derivative 421 in combination... 

When quadricyclane derivative 79 was pyrolyzed by Hoffmann and Schiitt-ler106 they detected ketene 74 as the only product. But the combination of flash... 

Acetic anhydride, with 2-hep-tanone to give 3-n-butyl-2, 4-pentanedione, 51, 90 ACETIC FORMIC ANHYDRIDE, 50, 1 Acetone azine, 50, 2 ACETONE HYDRAZONE, 50, 2, 28 Acetophenone, 54, 93 as sensitizer for irradiation of bicyclo[2.2.1]hepta-2,5-diene to give quadricyclane,... 

This same CIDNP study also ruled out the existence of the bishomo-aromatic system [158c] by finding two distinct species, [158a] and [158b], for the intramolecular cycloreversion of the radical cation of quadricyclane to that of norbornadiene. 

Triplet-sensitised photocycloaddition of norbornadiene (N) leads to formation of the energy-rich quadricyclane (Q) by an intramolecular reaction ... 

Although quadricyclane is highly strained, it is kinetically very stable on account of the large activation energy for the Q — N reaction. Use of suitable catalysts allows the stored solar energy to be released as heat. 

One of the interesting molecules that has been studied in considerable detail is nor-bomadiene (80). Much of this interest has been associated with the interactions between the double bonds of the system. Thus irradiation affords quadricyclane (81). This area of study will be discussed later in this chapter. The radical cation 82 can also be formed from both norbomadiene and quadricyclane by irradiation in acetonitrile/methanol solution with the DCB/phenanthrene sensitizer system. Several products (Scheme 2) are formed in low yield and it should be noted that there is little difference in the yields of products obtained from either starting material. However, it is evident that attack by methanol occurs from the exo face32. 

The incorporation of sulphonyl groups does not inhibit the cyclization process as demonstrated by Gleiter and Ohlbach133, who have reported the efficient synthesis of the quadricyclane 252 by irradiation of the norbornadiene derivatives 253. A study has also been made of the sulphonyl-substituted norbornadiene derivatives 254134 135. 

Like the cyclization of the parent system, the photocyclization of hetero analogues of norbornadiene was reported many years ago. Recent interest in this area will serve to illustrate the potential of the conversions. Thus the irradiation of the oxanorbomadiene system 259 brings about conversion to the oxepine 260138. The formation of 260 presumably arises by quadricyclane 261 formation, followed by secondary photolytic ring-opening. Other research has shown that irradiation of the oxanorbomadiene 262 follows the same reaction mode and it undergoes (2 + 2)-cycloaddition to the quadricyclane derivative 263. Apparently, in this instance, cycloreversion affords the ylide 264 that can be trapped by suitable addends, giving the adducts illustrated in Scheme 3139. 

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